Nitrogen heterocyclic carbon-rich materials: Synthesis and spectroscopic properties of dehydropyridoannulene macrocycles

Nitrogen Heterocyclic Carbon-Rich Materials: Synthesis and

Spectroscopic Properties of Dehydropyridoannulene Macrocycles

Paul N. W. Baxter* and Riad Dali-Youcef

Institut Charles Sadron, UPR 022, 6 Rue Boussingault, F-67083 Strasbourg, France

baxter@ics.u-strasbg.fr

Received October 27, 2004

A new series of nitrogen heterocyclic dehydroannulenes 1-3 have been synthesized and their

macrocyclic structures assigned using spectroscopic methods. The chiral and planar ground state

conformations of 1 and 3, respectively, were determined by semiempirical theoretical calculations.

All dehydropyridoannulenes and precursors possessing four aromatic rings functioned as fluorescent

chromophores. A detailed spectroscopic investigation into the cation-binding properties of 3 in dilute

solution revealed a particularly selective photoluminescence quenching sensory response for Pd^II

ions. Cycle 3, as well as 1 and 2, also exhibited reversible proton-triggered luminescence quenching

behavior. At higher concentrations, 3 afforded a coordination polymer precipitate with Ag^Iions.

Cycles 1 and 2 and precursors 15, 23, and 29 also undergo thermochemical reactions that may

potentially lead to carbon-rich polymers. The physicochemical properties of 1-3 suggest that

dehydropyridoannulenes may serve as a particularly versatile new class of ligands for the creation

of novel heteroatom-containing carbon-rich materials with many potential applications in supramo-

lecular materials science and nanotechnology.

Introduction

works has been very productive as a result of their ready

synthetic accessibility.^{1a-e,g,2b,c,f,h,3a-f}

Since the discovery of buckminsterfullerenes and car-

bon nanotubes, the synthesis and study of carbon-rich

organic materials has rapidly spread into a domain of

major scientific importance within the physical and

chemical community.^1a-gHowever, expanded carbon

network polymers, which have been theoretically pre-

dicted to possess many intriguing mechanical and

physicochemical properties, have so far eluded all at-

tempts at preparation due to the formidable synthetic

challenge of generating a defect-free lattice using con-

ventional covalent bond chemistry.^2a-kOn the other hand,

the preparation of ethynyl macrocycles which may serve

as precursors to hypothetical carbon-rich polymer net-

Of historical note, early reports in this field concen-

trated on the chemistry of dehydroannulene macrocycles,⁴

(2) (a) Narita, N.; Nagai, S.; Suzuki, S.; Nakao, K. Phys. Rev. B 1998,

58, 11009. (b) Bunz, U. H. F.; Rubin, Y.; Tobe, Y. Chem. Soc. Rev. 1999,

28, 107. (c) Eickmeier, C.; Holmes, D.; Junga, H.; Matzger, A. J.;

Scherhag, F.; Shim, M.; Vollhardt, K. P. C. Angew. Chem. 1999, 111,

856; Angew. Chem., Int. Ed. 1999, 38, 800. (d) Lange, T.; van Loon,

J.-D.; Tykwinski, R. R.; Schreiber, M.; Diederich, F. Synthesis 1996,

537. (e) Eaton, P. E.; Galoppini, E.; Gilardi, R. J. Am. Chem. Soc. 1994,

116, 7588. (f) Bunz, U. H. F. Angew. Chem. 1994, 106, 1127; Angew.

Chem., Int. Ed. Engl. 1994, 33, 1073. (g) Feldman, K. S.; Weinreb, C.

K.; Youngs, W. J.; Bradshaw, J. D. J. Am. Chem. Soc. 1994, 116, 9019.

(h) Diederich, F.; Rubin, Y. Angew. Chem. 1992, 104, 1123; Angew.

Chem., Int. Ed. Engl. 1992, 31, 1101. (i) Johnston, R. L.; Hoffmann,

R. J. Am. Chem. Soc. 1989, 111, 810. (j) Merz, K. M., Jr.; Hoffmann,

R.; Balaban, A. T. J. Am. Chem. Soc. 1987, 109, 6742. (k) Baughman,

R. H.; Eckhardt, H.; Kertesz, M. J. Chem. Phys. 1987, 87, 6687.

(3) (a) Zhao, D.; Moore, J. S. Chem. Commun. 2003, 807. (b) Gleiter,

R.; Werz, D. B.; Rausch, B. J. Chem. Eur. J. 2003, 9, 2676. (c) Grave,

C.; Schlu¨ter, A. D.; Eur. J. Org. Chem. 2002, 3075. (d) Kennedy, R.

D.; Lloyd, D.; McNab, H. J. Chem. Soc., Perkin Trans. 1 2002, 1601.

(e) Top. Curr. Chem. 1999, 201, whole volume. (f) Ho¨ger, S. J. Polym.

Sci., Part A: Polym. Chem. 1999, 37, 2685.

(1) (a) Nielsen, M. B.; Diederich, F. Chem. Rec. 2002, 2, 189. (b)

Nielsen, M. B.; Diederich, F. Synlett 2002, 544. (c) Bodwell, G. J.; Satou,

T. Angew. Chem., Int. Ed. 2002, 41, 4003. (d) Diederich, F. Chem.

Commun. 2001, 219. (e) Rubin, Y. Chem. Eur. J. 1997, 3, 1009. (f)

Terrones, H.; Terrones, M.; Hsu, W. K. Chem. Soc. Rev. 1995, 341. (g)

Diederich, F. Nature 1994, 369, 199.

Published on Web 05/28/2005

J. Org. Chem. 2005, 70, 4935-4953

4935

Baxter and Dali-Youcef

CHART 1

which rapidly diversified in parallel to that of the

structurally related annulenes, to encompass a wide

range of cyclic conjugated hydrocarbons. These systems

found use as model systems for the experimental verifi-

cation of aromaticity and Hu¨ckel theory.^5a-cIn particular,

dehydrobenzoannulenes are currently the focus of a surge

in interest as they offer potential for structural elabora-

tion into model sections of expanded carbon networks

which include graphyne and graphdiyne.^3d-e,6a-eSuch

cyclophanes have recently been demonstrated to exhibit

NLO,⁷photochromic,⁸and high-spin magnetic behavior,⁹

as well as serving as precursors for the generation of

carbon buckyonions and nanotubes,^10a-dand as interest-

ing novel strained-ring systems.^11a-eIn the area of

supramolecular chemistry, they have been reported to

function as assembly units for the generation of pseudo-

rotaxane-type architectures.¹²

An alternative to the covalent approach for the con-

struction of network polymers based on dehydroannulene

subunits would be to use supramolecular chemistry and,

in particular, metal ion-induced autoassembly. In the

latter situation, the mechanism of polymer formation will

be expected to occur via reversible metal ion-ligand

interactions in which errors are removed during growth

of the network. Polymers of this type may topologically

mimic those of the theoretically proposed carbon-rich

nets, but with the additional feature that they would

incorporate metal ions as integral structural units.

Materials of this type would be especially interesting in

that they may be expected to display a rich variety of

exploitable properties such as electrochemical, photo-

chemical, magnetic, optical, catalytic, porous, sensory,

and mechanical behavior.^13a-dWith the aforementioned

considerations as one of our goals, we have been develop-

ing a new class of heterocyclic dehydroannulene-type

cyclophanes over the past years that incorporates pyri-

dine rings as sites for metal ion complexation.^14a-rThese

investigations demonstrated that cycles 4-8 (Chart 1)

were strongly fluorescent chromophores affording char-

acteristic photoluminescence sensory output responses

in the presence of particular metal ions.

The present report discloses studies conducted in

parallel to those detailed above and dealing specifically

with the syntheses and spectroscopic properties of dehy-

droannulene macrocycles 1-3 (Chart 1). The preparation

of building blocks for the construction of related, isomeric

systems is also described, along with investigations into

the photoluminescence and thermal properties of the

macrocycles as well as the sensory behavior and coordi-

nation potential of 3 toward metal ions. The aromatic

rings within 1-3 are all ortho-connected, and may

therefore be regarded as true dehydropyrido-

annulenes.^5a,6c,15

(4) For a review containing early reports on dehydrobenzoannulenes,

see: Mitchell, R. H. Israel J. Chem. 1980, 20, 294.

(5) (a) Sondheimer, F. Acc. Chem. Res. 1972, 5, 81. (b) Okamura,

W. H.; Sondheimer, F. J. Am. Chem. Soc. 1967, 89, 5991. (c) Untch,

K. G.; Wysocki, D. C. J. Am. Chem. Soc. 1966, 88, 2608.

(6) For reviews on the syntheses of dehydrobenzoannulenes, see: (a)

Marsden, J. A.; Palmer, G. J.; Haley, M. M. Eur. J. Org. Chem. 2003,

2355. (b) Top. Curr. Chem. 1999, 201, 81-130. (c) Youngs, W. J.;

Tessier, C. A.; Bradshaw, J. D. Chem. Rev. 1999, 99, 3154. (d) Haley,

M. M. Synlett 1998, 557. (e) Meier, H. Synthesis 1972, 235.

(7) Sarkar, A.; Pak, J. J.; Rayfield, G. W.; Haley, M. M. J. Mater.

Chem. 2001, 11, 2943.

(8) Kimball, D. B.; Haley, M. M.; Mitchell, R. H.; Ward, T. R.;

Bandyopadhyay, S.; Williams, R. V.; Armantrout, J. R. J. Org. Chem.

2002, 67, 8798.

(9) Nishide, H.; Takahashi, M.; Takashima, J.; Pu, Y.-J.; Tsuchida,

E. J. Org. Chem. 1999, 64, 7375.

(10) (a) Laskoski, M.; Steffen, W.; Morton, J. G. M.; Smith, M. D.;

Bunz, U. H. F. J. Am. Chem. Soc. 2002, 124, 13814. (b) Glezakou, V.-

A.; Boatz, J. A.; Gordon, M. S. J. Am. Chem. Soc. 2002, 124, 6144. (c)

Dosa, P. I.; Erben, C.; Iyer, V. S.; Vollhardt, K. P. C.; Wasser, I. M. J.

Am. Chem. Soc. 1999, 121, 10430. (d) Boese, R.; Matzger, A. J.;

Vollhardt, K. P. C. J. Am. Chem. Soc. 1997, 119, 2052.

(11) For some recent examples of strained dehydrobenzoannulene

ring systems, see: (a) Tobe, Y.; Ohki, I.; Sonoda, M.; Niino, H.; Sato,

T.; Wakabayashi, T. J. Am. Chem. Soc. 2003, 125, 5614. (b) Boydston,

A. J.; Laskoski, M.; Bunz, U. H. F.; Haley, M. M. Synlett 2002, 981.

(c) Mitzel, F.; Boudon, C.; Gisselbrecht, J.-P.; Gross, M.; Diederich, F.

Chem. Commun. 2002, 2318. (d) Gallagher, M. E.; Anthony, J. E.

Tetrahedron Lett. 2001, 42, 7533. (e) Bunz, U. H. F.; Enkelmann, V.

Chem. Eur. J. 1999, 5, 263.

Results and Discussion

The syntheses of macrocycles 1-3 are shown in

Schemes 1-4. The most efficient general method of

(13) The metal ion directed assembly of coordination polymer

networks has been the subject of considerable effort. For recent reviews,

see: (a) Kitagawa, S.; Kitaura, R.; Noro, S. Angew. Chem., Int. Ed.

2004, 43, 2334. (b) Fe´rey, G. Chem. Mater. 2001, 13, 3084. (c) Hosseini,

M. W. In Crystal Engineering: From Molecules and Crystals to

Materials; Braga, D., Grepioni, F., Orpen, G. A., Eds.; Kluwer:

Dordrecht, 1999, pp 181-208. For an example of a three-dimensional

coordination polymer incorporating ethynylpyridyl-type ligands, see:

(d) Maekawa, M.; Konaka, H.; Suenaga, Y.; Kuroda-Sowa, T.; Mu-

nakata, M. J. Chem. Soc., Dalton Trans. 2000, 4160.

(12) Pak, J. J.; Weakley, T. J. R.; Haley, M. M.; Lau, D. Y. K.;

Stoddart, J. F. Synthesis 2002, 1256.

4936 J. Org. Chem., Vol. 70, No. 13, 2005

Nitrogen Heterocyclic Carbon-Rich Materials

SCHEME 1. Synthesis of o-Diethynylpyridine Precursors^a

^aKey: (i) TMSA, PdCl₂(PPh₃)₂, CuI cat., Et₃N, 20 °C, 5-7 d {10 (91%),^14c20 (96%)}; (ii) n-BuLi, Et₂O, -78 °C, 1.5 h, then ICH₂CH₂I/

Et₂O, -78 °C, 3 h {11 (86%),^14c19 (80%), 25 (93%)}; (iii) TIPSA, PdCl₂(PPh₃)₂, CuI cat., Et₃N, 20 °C, 5-7 d {12 (96%), 18 (87%); 75 °C,

3 d: 26 (64%)}; (iv) K₂CO₃, MeOH, 20 °C, 17-36h {13 (90%), 21 (99%), 27 (99%)}; (v) CuI or CuCl cat., O₂, pyridine, 20 °C, 18-48 h {14

(86%), 17 (79%), 22 (68%), 28 (65%)}; (vi) 1 M [(n-Bu)₄N]F, THF/H₂O, 20 °C, 14-36 h {15 (76%), 16 (91%), 23 (96%), 29 (65%), 30 (76%)}.

preparation of 1 and 2 utilized the pivotal monoprotected

diethynylpyridine 21, which was homologated via suc-

cessive Sonogashira coupling, selective desilylation, and

Hay coupling to afford tetraaryl precursors 33 and 38.

Further deprotection followed by copper-mediated in-

tramolecular cyclizations yielded 1 and 2 (Schemes 1-3).

Cycle 3 was obtained in low yield using the Stephens-

Castro intermolecular organocuprate cyclotrimerization

protocol (Scheme 4).

Synthesis of Dehydropyridoannulene Precursors

12-30. Unlike their dehydrobenzoannulene analogues,

dehydropyridoannulenes such as 1-3 and related sys-

tems may exist as a range of isomers depending upon

the relative positions of the pyridine nitrogens. Isomeric

dehydropyridoannulenes are interesting synthetic targets

as they will be expected to exhibit differing coordination

arrangements as well as spectroscopic and electrochemi-

cal properties. For example, the study of structure/

property relationships within a given library of isomeric

dehydropyridoannulenes may enable optimization of the

system for a particular function.¹⁶To obtain facile access

to isomeric dehydropyridoannulenes, a modular series of

o-diethynylpyridine building blocks were initially pre-

pared (Scheme 1), the syntheses of which are described

below.^17a-c

Initial synthetic work revealed that 3-bromo-4-iodo-

pyridine (9)^14c-18a-cserved as an ideal starting substrate

for the construction of the 3,4-diethynylpyridyl subunits.

Thus, 9 was converted via 10 to 11 as described in an

earlier paper.^14cThe Sonogashira¹⁹reaction of 11 with

TIPSA in Et₃N with PdCl₂(PPh₃)₂and CuI catalysts

afforded the o-diethynylpyridine 12 in 96% yield. Selec-

tive desilylation of 12 with K₂CO₃in MeOH proceded

cleanly to give 13 in 90% yield.²⁰Dipyridine 14 was

obtained in 86% yield from the Hay coupling^21a-cof 13

in oxygenated pyridine solution with CuI catalyst. Depro-

tection of 14 with [(n-Bu)₄N]F in THF provided the

particularly heat- and light-sensitive dehydropyrido-

annulene precursor 15 in 76% yield after workup.

In an alternative route to 15, iodopyridine 11 was

deprotected with [(n-Bu)₄N]F in THF to give 16 in 91%

yield and the latter coupled to afford 17 in 79% using

CuCl in oxygenated pyridine. However, the Sonogashira

reaction of 17 with TMSA in toluene/Et₃N provided the

J. Org. Chem, Vol. 70, No. 13, 2005 4937

Baxter and Dali-Youcef

SCHEME 2. Synthesis of Dehydrotetrapyrido[20]annulene 1^a

^aKey: (i) PdCl₂(PPh₃)₂, CuI cat. Et₃N, 20 °C, 5 d: 31 (75%); [PdCl₂(dppf)].CH₂Cl₂, CuI cat. toluene/Et₃N, 60 °C, 22 h: 33 (48%); (ii)

K₂CO₃, MeOH, 20 °C, 20 h (91%); (iii) CuCl cat., O₂, pyridine, 20 °C, 24 h (77%); (iv) 1 M [(n-Bu)₄N]F, THF, H₂O, 20 °C, 20 h (99%); (v)

[Cu₂(OAc)₄]‚2H₂O, pyridine, 20 °C, 21 d (40%).

SCHEME 3. Synthesis of Dehydrodibenzodipyrido[20]annulene 2^a

^aKey: (i) CuI cat., toluene/Et₃N {PdCl₂(PPh₃)₂cat., 20 °C, 6 d: 36 (77%); [PdCl₂(dppf)]‚CH₂Cl₂cat., 60 °C, 24 h: 42 (48%)}; (ii) K₂CO₃,

MeOH, 20 °C, 36 h (88%); (iii) CuCl cat., O₂, pyridine, 20 °C, 48 h (94%); (iv) [(n-Bu)₄N]F, THF, H₂O, 20 °C, 24 h (91%); (v) Cu₂(OAc)₄,

pyridine, 20 °C, 25 d (79%); (vi) n-BuLi, Et₂O, -78 to 0 °C, 1.2 h, then ICH₂CH₂I/Et₂O, -78 °C, 3 h (82%).

bis-trimethylsilyl analogue of 14 in only moderate yield

and accompanied by contaminants that could not be

removed by conventional column chromatography. This

may in part be due to the poor solubility of 17 and the

heat sensitivity of the desired reaction product. It may

be noted that 14 was stable to heat, in stark comparison

to 15, and could be stored indefinitely at ambient

temperature in the dark without any visible decomposi-

tion, highlighting the sterically stabilizing effect of the

TIPS substituents.

4938 J. Org. Chem., Vol. 70, No. 13, 2005

Nitrogen Heterocyclic Carbon-Rich Materials

SCHEME 4. Synthesis of

lation of 10 using standard Sonogashira conditions

resulted in products of inferior purity and lower yields.

Dehydrotripyrido[12]annulene 3^a

Diethynylpyridine 20 was then selectively desilylated

to 21 in 99% yield using conditions similar to those

employed for the generation of 13. The Hay coupling of

21 in oxygenated pyridine with CuCl provided the heat

stable 22 in 68% yield, which was subsequently depro-

tected in an identical way to that of 14 to afford precursor

23 in 96% yield.

^aKey: (i) CuSO₄‚5H₂O, aq NH₃, NH₂OH.HCl, EtOH (95%); (ii)

pyridine, 145 °C, 18 h (5%).

The o-diethynyl isomer 29 was obtained from bromo-

pyridine 24²²using the same synthetic route as that for

the preparation of 15 and 23 from 10 and 18, respec-

tively. Thus, the low-temperature lithiation of 24 followed

by treatment with ICH₂CH₂I afforded 25 in 93% yield.

The coupling reaction between 25 and TIPSA in Et₃N

with PdCl₂(PPh₃)₂and CuI catalysts proved to be sur-

prisingly sluggish at ambient temperature. However,

subsequent heating of the reaction at 75 °C for 3 d

resulted in complete consumption of 25 and the isolation

of 26 in 64% yield. Selective K₂CO₃-mediated desilylation

of 26 gave 27 in 99% yield which was then coupled to

afford 28 in 65% yield and the latter finally deprotected

to provide 29 in 65% yield after workup. In a similar way

to the deprotection of 11 to 16, the [(n-Bu)₄N]F-mediated

desilylation of 25 afforded ethynylpyridine 30, which was

obtained in 76% yield. With a modular palate of simple

macrocycle precursors in hand, synthetic strategies to-

ward the construction of dehydropyridoannulene archi-

tectures could then be explored.

Synthesis and Characterization of 1. In earlier

work, cycles 7 and 8 were discovered to exhibit interest-

ing luminescence and metal ion sensory properties. These

materials comprise pyridines at the corners and bridging

aromatic rings incorporated into the sides of the macro-

cyclic architecture.

With the eventual goal of generating 3-D coordination

networks with novel physicochemical properties, it was

obviously of high interest to evaluate the luminescence

and metal coordination properties of the structurally

related cycle 1, a nitrogen heterocyclic analogue of

dehydrotetrabenzo[20]annulene.^10d

The synthesis of 1 was successfully accomplished using

a route with two initially differing approaches to the

common intermediate 33 (Scheme 2). In the first ap-

proach, iodopyridine 11 and diethynylpyridine 21 were

coupled in Et₃N with PdCl₂(PPh₃)₂and CuI catalysts to

afford 31 in 75% yield. Dipyridine 31 was selectively

desilylated with K₂CO₃in MeOH to give 32 in 91% yield

and the latter coupled in the presence of CuCl catalyst

in oxygenated pyridine to provide 33 in 77% yield. In the

second approach, 33 was obtained in 48% yield upon a

Sonogashira reaction between 19 and 15. The catalyst

[PdCl₂(dppf)]‚CH₂Cl₂was found to give superior quanti-

ties of product compared to PdCl₂(PPh₃)₂. The moderate

yield of 33 in this case is partly attributable to the limited

solubility and heat sensitivity of precursor 15. When the

latter reaction was conducted in Et₃N or THF at ambient

temperature, the 15 failed to dissolve and slowly decom-

posed, subsequent heating also accelerated its decompo-

sition. Hot toluene was found to be the most suitable

solvent for the coupling reaction as it solubilized 15 with

a minimal amount of degradation. The heat stable 33 was

then deprotected with [(n-Bu)₄N]F to afford 34 in 99%

To prepare the isomeric dehydropyridoannulene pre-

cursor 23, iodopyridine 9 was first converted to 18 in 87%

yield, using conditions identical to those for the synthesis

of 12 from 11. Ethynylpyridine 18 was then lithiated at

low temperature with n-BuLi in Et₂O and cleanly iodi-

nated with ICH₂CH₂I to 19 in 80% yield. The reaction

between 19 and TMSA in Et₃N with PdCl₂(PPh₃)₂and

CuI catalysts afforded 20 in 96% yield. The latter reaction

sequence was performed in an analogous way to that of

the indirect synthesis of 12 from 10 via 11, as the more

reactive iodopyridine 11 was found to be a superior

coupling partner. Earlier attempts at the direct ethyny-

(14) The construction of ethynyl macrocycles incorporating pyridine

and pyridine-type heterocycles has recently been the focus of a surge

in interest. For examples incorporating pyridine units, see: (a) Baxter,

P. N. W. J. Org. Chem. 2004, 69, 1813. (b) Yamaguchi, Y.; Kobayashi,

S.; Miyamura, S.; Okamoto, Y.; Wakamiya, T.; Matsubara, Y.; Yoshida,

Z. Angew. Chem., Int. Ed. 2004, 43, 366. (c) Baxter, P. N. W. Chem.

Eur. J. 2003, 9, 2531. (d) Campbell, K.; McDonald, R.; Ferguson, M.

J.; Tykwinski, R. R. Organometallics 2003, 22, 1353. (e) Campbell, K.;

McDonald, R.; Tykwinski, R. R. J. Org. Chem. 2002, 67, 1133. (f)

Campbell, K.; McDonald, R.; Branda, N. R.; Tykwinski, R. R. Org. Lett.

2001, 3, 1045. (g) Sun, S.-S.; Lees, A. J. Organometallics 2001, 20,

2353. (h) Bosch, E.; Barnes, C. L. Organometallics 2000, 19, 5522. (i)

Tobe, Y.; Nagano, A.; Kawabata, K.; Sonoda, M.; Naemura, K. Org.

Lett. 2000, 2, 3265. (j) Tobe, Y.; Nakanishi, H.; Sonoda, M.; Wakaba-

yashi, T.; Achiba, Y. J. Chem. Soc., Chem. Commun. 1999, 1625. For

examples of conjugated ethynyl macrocycles incorporating bipyridine

units, see: (k) Venturi, M.; Marchioni, F.; Balzani, V.; Opris, D. M.;

Henze, O.; Schlu¨ter, A. D. Eur. J. Org. Chem. 2003, 4227. (l) Baxter,

P. N. W. Chem. Eur. J. 2002, 8, 5250. (m) Henze, O.; Lentz, D.; Scha¨fer,

A.; Franke, P.; Schlu¨ter, A. D. Chem. Eur. J. 2002, 8, 357. (n) Baxter,

P. N. W. J. Org. Chem. 2001, 66, 4170. (o) Henze, O.; Lentz, D.;

Schlu¨ter, A. D. Chem. Eur. J. 2000, 6, 2362. (p) Henze, O.; Lehmann,

U.; Schlu¨ter, A. D. Am. Chem. Soc. Polym. Mater. Sci. Eng. 1999, 80,

231. For ethynyl macrocycles incorporating terpyridine units, see: (q)

Grave, C.; Lentz, D.; Scha¨fer, A.; Samori, P.; Rabe, J. P.; Franke, P.;

Schlu¨ter, A. D. J. Am. Chem. Soc. 2003, 125, 6907. (r) Baxter, P. N.

W. Chem. Eur. J. 2003, 9, 5011.

(15) The term “true dehydroarylannulene” is used in this context

to exclude arene cyclynes in which one or more of the bridging aryl

groups exhibit meta-, para-, and other types of non-ortho-connectivity.

(16) . Although the pyridine nitrogens can be arranged in 64 possible

ways within 3, the macrocycle is actually one of only 12 different

regioisomers due to symmetry overlaps. For the same reason, 2 is one

of 10 different regioisomers generated from 16 possible pyridine

nitrogen arrangements. However in 1, there are 256 possible pyridine

nitrogen arrangements giving rise to 76 different regioisomers!

(17) Reports on the syntheses of o-diethynylpyridines are rare.

See: (a) ref 14c. (b) Kim, C.-S.; Russell, K. C. J. Org. Chem. 1998, 63,

8229. (c) Gibson, K. J.; d’Alarcao, M.; Leonard, N. J. J. Org. Chem.

1985, 50, 2462.

(18) (a) Talik, T.; Talik, Z. Roczniki Chem. 1962, 36, 539. (b) Talik,

T. Roczniki Chem. 1962, 36, 1049. (c) Imahori, T.; Uchiyama, M.;

Sakamoto, T.; Kondo, Y. Chem. Commun. 2001, 2450.

(19) Sonogashira, K.; Tohda, Y.; Hagihara, N. Tetrahedron Lett.

1975, 4467.

(20) Bell, M. L.; Chiechi, R. C.; Johnson, C. A.; Kimball, D. B.;

Matzger, A. J.; Wan, W. B.; Weakley, T. J. R.; Haley, M. M. Tetrahedron

2001, 57, 3507.

(21) (a) Hay, A. S. J. Org. Chem. 1962, 27, 3320. (b) Hay, A. S. J.

Org. Chem. 1960, 25, 1275. For an example of the application of the

Hay procedure to the synthesis of polypyridylbutadiynes, see: (c)

Grosshenny, V.; Romero, F. M.; Ziessel, R. J. Org. Chem. 1997, 62,

1491.

J. Org. Chem, Vol. 70, No. 13, 2005 4939

Baxter and Dali-Youcef

yield.²³Diethyne 34 was found to be somewhat more

stable to heat and light than its precursor 15, although

its ambient temperature solubility in a range of organic

solvents remained comparable.

Final intramolecular cyclization of 34 into 1 was

achieved using the Eglinton-Galbraith protocol that had

been found to be most successful for the preparation of 7

and 8.²⁴Thus, 34 was cyclized under medium/high

dilution conditions in degassed pyridine with an excess

of [Cu₂(OAc)₄]‚2H₂O to afford 1 in 40% isolated yield.

Cycle 1 was found to be stable in refluxing toluene at

110 °C, but underwent color darkening upon exposure

to daylight over days to weeks.

The proposed structure of the product isolated from the

coupling of 34 was established to be that of 1 (Scheme 2)

on the basis of mass spectroscopic, infrared, and ¹H and

1

¹³C NMR spectroscopic studies including H-¹H COSY

and H-¹³C HSQC/HMQC measurements.

1

FIGURE 1. 400 MHz H (upper) and 100.6 MHz ¹³C (lower)

The FAB mass spectrum of the coupling product

displayed a single isotope cluster peak at m/z ) 453,

matching that calculated for the [M⁺+ H] isotopic

envelope of macrocycle 1. This structural assignment was

further substantiated by a high-resolution FAB mass

spectroscopic measurement of the [M⁺+ H] isotopic

envelope, which confirmed the exact elemental composi-

tion of the product to be C₃₂H₁₃N₄, in accordance with

the macrocyclic structure 1 plus one hydrogen.

NMR spectra of 1, recorded in CDCl₃solution at 25 °C.

In the infrared spectrum of 1, vibrational modes

characteristic of the H-Ct stretch of terminal alkynes

were absent, establishing that the coupling product is a

macrocycle, and not a linear oligomer with unreacted

terminal ethyne groups.

FIGURE 2. Energy-minimized structure of macrocycle 1.

Left: plan view (stick representation). Center: plan view (CPK

representation). Right: view through central macrocyclic

cavity. The minimization was obtained by an AM1 semi-

empirical calculation using SPARTAN 02 Linux/Unix, Wave-

function, Inc., Irvine, CA.

The ¹³C NMR spectrum comprised eight peaks, con-

sistent with the above macrocyclic structural assignment

for 1 (Figure 1). The chemical shifts of the three peaks

in the range 91.5-80.1 ppm correspond to the chemically

and magnetically inequivalent carbons of the butadiynes

and the equivalent carbons of the bridging alkyne groups.

The remaining five peaks originate from the carbons of

the pyridines.

compound and not a mixture of species. Peaks originating

from the protons of terminal ethynes were absent in the

¹H NMR spectrum, lending further support for the

macrocyclic identity of this compound. Spectral assign-

ments were made on the basis of coupling constants and

spectral comparisons with the precursors.

A semiempirical AM1 molecular modeling calculation

performed upon the structure assigned to 1 showed the

ground-state conformation to be that of a strain-free

twisted, chiral macrocycle, with a small internal void

(Figure 2).²⁵

Synthesis and Characterization of 2. A further

avenue of interest would be to generate dehydroannulene

coordination polymers of lower dimensionality than those

expected for 1. Polymers of this type may function as

conjugated wires and new luminescent materials, but

with additional structural features such as enhanced

conjugation and chirality.^26a-gToward this goal, the

exotopic bidentate macrocycle 2 was synthesized, which

is a structural hybrid between 1 and dehydrotetrabenzo-

[20]annulene, the benzo-analogue of 1.

The ¹H NMR spectrum displayed three resonances

expected for the macrocyclic structure 1 (Figure 1). A ¹H-

¹H COSY measurement verified that it was a single

(22) Sakamoto, T.; Nagata, H.; Kondo, Y.; Sato, K.; Yamanaka, H.

Chem. Pharm. Bull. 1984, 32, 4866.

(23) Unambiguous assignments of the NMR proton resonances of

31-33 to their respective pyridine rings were achieved using COSY,

NOESY and ROESY measurements. First, the COSY spectral connec-

tivities revealed the groups of protons that originated from the same

pyridine rings. Second, the NOESY and ROESY spectra displayed

characteristic “through-space” interactions identifying the particular

substituted ring to which each group of pyridine protons belonged. For

example, molecular modeling indicated that the TIPSA substituent in

31-33 contributed to hindered rotation of all the pyridines, and

suggestive of a strong “through-space” interaction between the TIPS

and the 2H protons of the pyridines without the TIPSA groups. In each

case, a strong NOESY cross-peak was indeed observed between the

signals due to the TIPS group and one of the pair of peaks correspond-

ing to the pyridine 2H protons. The pyridine 2H contributing to the

cross-peak with the TIPS group was therefore assignable to the ring

which did not bear the TIPSA substituent. The NOESY spectra of 31-

33 displayed additional evidence supportive of the latter assignments,

which in each case comprised a weaker cross-peak between the TIPS

signal and that of the adjacent 5H proton connected to the same

pyridine ring. In 32, an NOESY cross-peak was also observable

between the TIPS signal and that of the terminal alkyne proton. The

protons of 34 were assigned on the basis of NMR spectral comparisons

with 32 and 33.

A viable route to 2 was developed utilizing dieth-

ynylpyridine 21 (Scheme 3). Thus, 36 was isolated from

(25) For an example of the use of semiempirical AM1 calculations

for successfully predicting the conformations of ethynyl macrocycles,

see: Srinivasan, M.; Sankararaman, S.; Hopf, H.; Dix, I.; Jones, P. G.

J. Org. Chem. 2001, 66, 4299.

(24) Rossa, L.; Vo¨gtle, F. Top. Curr. Chem. 1983, 113, 72-75.

4940 J. Org. Chem., Vol. 70, No. 13, 2005

Nitrogen Heterocyclic Carbon-Rich Materials

the Sonogashira reaction between 21 and 35¹⁴ⁿin 77%

yield and then selectively desilylated with K₂CO₃in

MeOH to afford 37 in 88% yield after workup. Dieth-

ynylpyridine 37 was subsequently self-coupled with CuCl

catalyst in oxygenated pyridine to give 38 in 94% yield

and the latter deprotected with [(n-Bu)₄N]F to afford 39

in 91% yield after purification. The intramolecular cy-

clization of 39 was again most effectively accomplished

using excess Cu₂(OAc)₄under medium/high dilution

conditions in degassed pyridine to provide 2 in a par-

ticularly good yield of 79%.²⁷Cycle 2 was similar to 1

with respect to its stability toward heat and light.

In parallel to the above synthesis, an alternative route

to 2 was also investigated using 15 and 41. Iodophenyl

41 was prepared from 40²⁸via the halogen-exchange

protocol previously used for the synthesis of 11, 19, and

25. Thus, the palladium-catalyzed coupling between 15

and 41 using identical conditions to that of the generation

of 33 from 15 and 19 afforded 42 in 48% yield. However,

this route to 2 was abandoned in favor of the former, as

it offered no further advantage in terms of improved

overall yield.

The macrocyclic structural formulation of 2 (Scheme

3) was established using the same spectroscopic tech-

niques as in 1. The FAB mass spectrum exhibited a single

isotope cluster peak at m/z ) 451, corresponding to the

calculated [M⁺+ H] isotopic envelope of macrocycle 2.

The high-resolution FAB mass spectroscopic measure-

ment of the [M⁺+ H] isotopic envelope confirmed the

exact elemental composition of the product to be C₃₄H₁₅N₂.

The ¹³C NMR spectrum exhibited the expected seven-

teen peaks, i.e., six peaks from 94.9 to 78.0 ppm corre-

sponding to the carbons of the bridging alkyne groups,

and the remaining eleven originating from the carbons

of the aryl rings (Figure 3). The phenyl C3/6 and C4/5

carbons as well as the pyridine C5 carbon were addition-

ally assigned on the basis of ¹³C DEPT measurements.

Vibrational modes and peaks characteristic of the

FIGURE 3. 400 MHz ¹H (a) and 100.6 MHz ¹³C NMR spectra

of 2 (showing (b) aromatic region, (c) expansion of phenyl C4/5

and pyridyl C5 resonances, (d) alkyne region), recorded in

CDCl₃solution at 25 °C.

(n ) 12, 18) have attracted a considerable amount of

interest.^6a-dFor example, they have been used as precur-

sors for the attempted construction of sections of the

hypothetical carbon polymer networks graphyne and

graphdiyne and have also been demonstrated to exhibit

a rich coordination chemistry involving metal complex-

ation to the triple bonds.^6cSurprisingly, very few studies

have been reported on the synthesis and properties of

heterocyclic analogues of dehydrotriaryl[n]annulenes

other than those incorporating thiophene rings.^30a-jWe

therefore describe below some of our hitherto unpub-

1

H-Ct group were absent in the infrared and H NMR

(Figure 3) spectra, again supportive of a macrocyclic

rather than linear oligomeric or polymeric material. ¹H-

¹H COSY measurements also verified that it was a single

compound and not a mixture of species.

Synthesis and Characterization of 3. Since the first

reported independent syntheses of dehydrotribenzo[12]-

annulene by Staab and Eglinton and their respective co-

workers,^29a-btriangular dehydrotriaryl[n]annulenes

(26) For the generation of 1-D coordination polymers using eth-

ynylpyridine-type ligands, see: (a) Kim, H.-J.; Zin, W.-C.; Lee, M. J.

Am. Chem. Soc. 2004, 126, 7009. (b) Zaman, Md. B.; Smith, M. D.; zur

Loye, H.-C. Chem. Commun. 2001, 2256. (c) Fiscus, J. E.; Shotwell,

S.; Layland, R. C.; Smith, M. D.; zur Loye, H.-C.; Bunz, U. H. F. Chem.

Commun. 2001, 2674. (d) Jouaiti, A.; Jullien, V.; Hosseini, M. Wais.;

Planeix, J.-M.; De Cian, A. Chem. Commun. 2001, 1114. (e) Ciurtin,

D. M.; Pschirer, N. G.; Smith, M. D.; Bunz, U. H. F.; zur Loye, H.-C.

Chem. Mater. 2001, 13, 2743. (f) ref 13d. (g) Blake, A. J.; Champness,

N. R.; Khlobystov, A.; Lemenovskii, D. A.; Li, W.-S.; Schro¨der, M. Chem.

Commun. 1997, 2027.

(29) (a) Staab, H. A.; Graf, F. Tetrahedron Lett. 1966, 751. (b)

Campbell, I. D.; Eglinton, G.; Henderson, W.; Raphael, R. A. Chem.

Commun. 1966, 87.

(30) For dehydroannulenes incorporating nitrogen heterocycles,

see: (a) Ott, S.; Faust, R. Synlett. 2004, 1509. (b) Garc´ıa-Frutos, E.

M.; Ferna´ndez-La´zaro, F.; Maya, E. M.; Va´zquez, P.; Torres, T. J. Org.

Chem. 2000, 65, 6841. (c) van Roosmalen, J. H.; Jones, E.; Kevelam,

H. Tetrahedron Lett. 1972, 13, 1865. It may be noted however that in

the former two references, the alkynes are not directly connected to

the heterocyclic rings but are actually connected to benzenes which

are fused to the heterocycles. For reports on the syntheses of dehy-

droannulenes incorporating thiophenes, see: (d) Boydston, A. J.; Haley,

M. M.; Williams, R. V.; Armantrout, J. R. J. Org. Chem. 2002, 67, 8812.

(e) Marsella, M. J.; Piao, G.; Tham, F. S. Synthesis 2002, 1133. (f)

Marsella, M. J.; Wang, Z.-Q.; Reid, R. J.; Yoon, K. Org. Lett. 2001, 3,

885. (g) Sarkar, A.; Haley, M. M. Chem. Commun. 2000, 1733. (h)

Zhang, D.; Tessier, C. A.; Youngs, W. J. Chem. Mater. 1999, 11, 3050.

(i) Iyoda, M.; Vorasingha, A.; Kuwatani, Y.; Yoshida, M. Tetrahedron

Lett. 1998, 39, 4701. (j) Solooki, D.; Bradshaw, J. D.; Tessier, C. A.;

Youngs, W. J. Organometallics 1994, 13, 451.

(27) The yield disparity between 1 (40%) and 2 (79%) is somewhat

surprising considering the similarity in reaction conditions and

workup. It may be noted however, that the cyclization of 34 to 1 was

effected using [Cu₂(OAc)₄]‚2H₂O, whereas anhydrous Cu₂(OAc)₄was

used for the cyclisation of 39 to 2. The presence of coordinated water

may exert a detrimental effect upon the cyclization reaction in specific

cases, but further experimental investigations will be necessary in

order to verify this hypothesis.

(28) Collins, S. K.; Yap, G. P. A.; Fallis, A. G. Angew. Chem., Int.

Ed. 2000, 39, 385.

J. Org. Chem, Vol. 70, No. 13, 2005 4941

Baxter and Dali-Youcef

FIGURE 5. Energy-minimized structure of macrocycle 3 (plan

view). Left: stick representation. Right: CPK representation.

The minimization was obtained by an AM1 semiempirical

calculation using SPARTAN 02 Linux/Unix, Wavefunction,

Inc., Irvine, CA.

to a tris(pyridocyclobutadieno)benzene system had not

occurred.^32a,bThe FAB mass spectrum exhibited a single

cluster peak at m/z ) 304 corresponding to the [M⁺+ H]

ion of 3, and the high-resolution FAB mass spectrum of

the [M⁺+ H] isotopic envelope confirmed the elemental

composition of the product to be C₂₁H₁₀N₃. A semi-

empirical AM1 calculation confirmed 3 to possess a rigid,

strain-free planar geometry with a small internal void

(Figure 5).

1

FIGURE 4. 500 MHz H (upper) and 125.8 MHz ¹³C (lower)

NMR spectra of 3, recorded in CDCl₃solution at 25 °C; [3] )

3.3 × 10^-2M.

Interestingly, the ¹H NMR spectrum of 3 in CDCl₃was

concentration dependent. For example, reducing the [3]

from 3.3 × 10^-2M (a saturated solution at 25 °C) to 1.3

× 10^-3M resulted in a downfield shift of all protons H2,

H6, and H5 by ∆δ ) 0.023, 0.020, and 0.024 ppm,

respectively. The latter behavior was reversible and is

indicative of an aggregation/deaggregation process, medi-

ated by π-π interactions, which would be expected of a

rigid, planar molecule such as 3. Thus, the net deshield-

ing of the protons of 3 upon dilution is consistent with

the breaking up of aggregates.

Spectroscopic Properties of 1, 2, and Precursors

33, 34, 38, 39, and 42. Solutions of 1 and 2 in CH₂Cl₂

displayed similar UV-vis spectra which exhibited two

high energy absorptions at 255-269 nm with relatively

large extinction coefficients where ꢀ ) (1.20-1.29) × 10⁵

M^-1cm^-1. In both cycles, a series of three to four poorly

resolved absorption envelopes were also observable at

lower energies between 294 and 354 nm with consider-

ably reduced extinction coefficients where ꢀ ) (0.10-0.35)

× 10⁵M^-1cm^-1(Figures 6 and 7). All absorptions were

invariant in energy and shape below 3.9 × 10^-5M,

showing that 1 and 2 were not aggregating in dilute

solution.

The UV-vis spectra of the precursors 33, 34, 38, 39,

and 42 were also similar to each other, comprising one

to two relatively high energy absorptions within the

range 237-253 nm and a series of three to four lower

energy absorptions between 284 and 375 nm, which were

particularly well resolved in 39 (Figures 6 and 7). In 33

and 34, all absorptions were invariant in energy and

shape below 8.8 × 10^-5M, showing that these precursors

were not aggregating in dilute solution. However, the

intense bands from 237 to 253 nm in the spectra of 38,

39, and 42, broadened and shifted 2-3 nm to lower

energy at concentrations higher than 5 × 10^-5M. The

precursors incorporating both phenyl and pyridyl rings

lished results on the synthesis and spectroscopic proper-

ties of 3, a dehydrotripyrido[12]annulene.

The synthesis of 3 was accomplished in two steps from

16 as shown in Scheme 4. Thus, treatment of an argon-

purged aqueous ammoniacal solution of CuSO₄‚5H₂O

with NH₂OH‚HCl, followed by addition of 16, resulted

in the formation of the highly insoluble cuprate 43, which

was isolated in 95% yield. Cyclotrimerization of 43 using

the classical Stephens-Castro protocol afforded 3 as the

sole cyclic product in 5% yield after purification. Cycle 3

exhibited greater stability toward heat and light com-

pared to 1 and 2.

The low yield of 3 is in sharp contrast to that of the

reported 48% for the related Stephens-Castro cyclization

to give dehydrotribenzo[12]annulene.^31aAn explanation

may lie in the possibility that cuprate 43 exists as a linear

or cross-linked coordination polymer in the solid state,

held together by Cu-N and Cu-alkyne coordination

interactions. In such a situation, polymer formation

would negate against cyclization by clamping the iodine

and copper reaction sites into fixed arrangements, at

distances and angles unfavorable for intramolecular ring

closure. The heterogeneous nature of the cyclization

reaction lends further support to the possibility that 43

is an insoluble coordination polymer.

The macrocyclic structural formulation of 3 (Scheme

4) was established as for 1 and 2, on the basis of multiple

spectroscopic studies. The ¹H and ¹³C NMR spectra

comprised the expected three and seven peaks, respec-

tively (Figure 4). In the case of the ¹H NMR and infrared

spectra, peaks characteristic of the H-C≡ group were

absent. The infrared spectrum of the cyclization product

displayed two bands at 2227 and 2212 cm^-1due to the

presence of a CtC bond, indicating that isomerization

(31) (a) Solooki, D.; Ferrara, J. D.; Malaba, D.; Bradshaw, J. D.;

Tessier, C. A.; Youngs, W. J.; John, J. A.; Tour, J. M. Inorg. Synth.

1997, 31, 122. For an alternative preparation of dehydrotribenzo[12]-

annulene by cyclotrimerisation of 2-bromophenylacetylene under phase

transfer conditions using [Pd(PPh₃)₄]/CuI catalysts, see: (b) Huynh,

C.; Linstrumelle, G. Tetrahedron 1988, 44, 6337.

(32) (a) Nambu, M.; Mohler, D. L.; Hardcastle, K.; Baldridge, K. K.;

Siegel, J. S. J. Am. Chem. Soc. 1993, 115, 6138. (b) Diercks, R.;

Vollhardt, K. P. C. J. Am. Chem. Soc. 1986, 108, 3150.

4942 J. Org. Chem., Vol. 70, No. 13, 2005

Nitrogen Heterocyclic Carbon-Rich Materials

FIGURE 6. UV-vis absorption spectra of 1 and precursors

33 and 34 recorded in CH₂Cl₂solution and also 1 in CH₂Cl₂

(0.1 M in CF₃CO₂H) at 25 °C.

FIGURE 8. Normalized fluorescence emission spectra of 1,

2, 33, 34, 38, 39, and 42 recorded in CH₂Cl₂solution at 25 °C.

(See the Experimental Section for the respective excitation

energies and solution concentrations.)

as CF₃CO₂H (Figures 6 and 7). Treatment of the acidified

solutions of 1 and 2 with aqueous Na₂CO₃resulted in

regeneration of the original free ligand spectra, verifying

that reversible protonation was occurring rather than

irreversible chemical reactions.

Solutions of 1, 2, 33, 34, 38, 39, and 42 in organic

solvents were fluorescent when exposed to UV light. The

emissions of 1 and 2 in aerated and deoxygenated CH₂-

Cl₂solution each comprised a single broad maximum at

443 and 456 nm, respectively, when excited within their

lower energy absorption envelopes (Figure 8). The excited

states of 1 and 2 were therefore insensitive to quenching

by oxygen. The energy of the emission maxima also

remained unchanged below 8.8-9.8 × 10^-5M, showing

that excited-state aggregation of the cycles was not

occurring in dilute solution.

FIGURE 7. UV-vis absorption spectra of 2 and precursors

38, 39, and 42 recorded in CH₂Cl₂solution and also 2 in CH₂-

Cl₂(0.1 M in CF₃CO₂H) at 25 °C.

The fluorescence spectra of precursors 33 and 34 were

virtually identical, comprising a relatively sharp emission

at 391-393 nm and a broader shoulder at 414 nm. The

fluorescence spectra of 38 and 39 were also very similar,

exhibiting a sharp emission at 378-379 nm and two

shoulders at 397 and 407-409 nm, respectively (Figure

8). The TIPS substituents therefore exercise a negligible

effect upon the excited-state energies of the precursors.

The emission of 1 on the other hand, is 51 nm lower in

energy than that of the averaged highest energy emis-

sions of 33 and 34. The emission of 2 is 77 nm lower in

energy than that of the highest energy emissions of its

precursors 38 and 39. Cyclization therefore causes a

significant lowering of the excited-state energies com-

pared to that of the precursors. Interestingly, the fluo-

rescence spectrum of 42 was unlike those of 33, 34, 38,

and 39, comprising a single broad emission at 417 nm,

and of intermediate energy between the latter precursors

and the cycles 1 and 2 (Figure 8). The inclusion of both

phenyl and pyridyl aromatic units within the macrocyclic

structures therefore result in a lowering of the excited-

state energies. The differences in emission energies

between the 33/34 pair and 42 also suggests that varia-

tion of the relative arrangements of phenyl versus pyridyl

rings within these systems may be used to controllably

tune their fluorescence energies.

may thus be undergoing some degree of ground-state

aggregation at, and above, the latter concentration

threshold.

Although the overall shape of the UV-vis spectra of

all compounds studied were approximately similar, dif-

ferences in detail were evident upon comparison of the

spectra of the macrocycles with the precursors. For

example, the 255-269 nm absorptions in 1 and 2 are

shifted to slightly lower energy compared to the related

absorptions of the precursors at 237-253 nm. The

extinction coefficients of the 255-269 nm absorptions in

1 and 2 are also significantly higher than those of the

237-253 nm precursor absorptions, which lie within the

range (0.69-0.85) × 10⁵M^-1cm^-1

.

However, the overall absorptions of 38, 39, and 42 from

280 to 370 nm occur at relatively higher extinction

coefficients compared to that of 2 within the same

wavelength range. In addition, the lower energy absorp-

tion complex of 42 extends to 400 nm. A similar trend is

found for 33 and 34, where the overall absorption curves

from 280 to 380 nm occur at higher extinction coefficients

and tail to a lower energy compared to that of 1 within

the same wavelength range. Finally, the UV-vis absorp-

tion spectra of CH₂Cl₂solutions of 1 and 2 were found to

be sensitive to the presence of strong organic acids such

J. Org. Chem, Vol. 70, No. 13, 2005 4943

Baxter and Dali-Youcef

FIGURE 9. Luminescence emission spectra of 2 with incre-

mental additions of CF₃CO₂H at [2] ) 9.8 × 10^-5M in CH₂Cl₂

and [H⁺] of, respectively, 1 × 10^-4, 1 × 10^-3, 1 × 10^-2, 1 ×

10^-1, and 1.0 M. The spectra were recorded 48 h after solution

preparation (λ_ex) 318 nm).

FIGURE 10. UV-vis spectra (left) of 3 in CH₂Cl₂(s), 3 in

CH₂Cl₂/0.1 M CF₃COOH (- ‚ ‚), 1:3 3/PdCl₂(MeCN)₂in 10%

MeOH/CH₂Cl₂(‚ ‚ ‚), and fluorescence emission spectrum

(right, s) in CH₂Cl₂.

tion was absent in dilute solution. The fluorescence

spectra of aerated and argon-bubbled solutions of 3 were

also identical, eliminating the possibility of oxygen-

mediated excited-state quenching. Interestingly, 3 ex-

hibited a rather large Stokes shift of 206 nm between

the highest intensity absorption and emission bands

(Figure 10).

As stated above, cycles 4-8 are strongly fluorescent

chromophores which were discovered to function as

highly effective luminescence sensors for particular metal

ions. Of the macrocycles 1-3 reported herein, cycle 3

exhibits the greatest structural differences compared to

4-8. It was therefore anticipated that 3 would also

exhibit significantly different luminescence sensory prop-

erties toward metal ions.³³

A detailed UV-vis spectroscopic investigation into the

ion-binding properties of 3 with 1:3 stoichiometric mix-

tures of 3/Mⁿ⁺in 10% MeOH/CH₂Cl₂, where [3] ) 5.4 ×

10^-6M and Mⁿ⁺) Li^I, Na^I, K^I, Mg^II, Ca^II, Cr^III, Mn^II, Fe^II,

Co^II, Ni^II, Pt^II, Au^I, Ag^I, Cu^I, Cu^II, Zn^II, Cd^II, Hg^II, Pb^II,

Tl^I, Al^III, In^III, Sc^III, Y^III, La^III, Eu^III, and Tb^III, showed zero

or minimal changes compared to the spectrum of pure 3,

indicating insignificant binding of the macrocycle to the

above cations in dilute solution.³⁴However, the UV-vis

spectra of 1:3 3/Pd^IIin 10% MeOH/CH₂Cl₂and 3/CF₃-

CO₂H in CH₂Cl₂, where [3] ) 5.4 × 10^-6M and [H⁺] )

0.1 M, were significantly different from the spectrum of

pure 3, demonstrating that Pd^IIcoordination and proto-

nation was occurring (Figure 10). The fluorescence emis-

It may also be noted that the fluorescence emissions

of 33, 34, 38, 39, and 42 in aerated and deoxygenated

CH₂Cl₂solution also remained identical in shape and

energy, showing that their excited states were insensitive

to quenching by oxygen. Interestingly, the highest energy

emissions of 33, 34, 38, and 39 exhibited 2-3 nm shifts

to lower energy at concentrations g7 × 10^-5M, suggest-

ing that excited-state aggregation phenomena were

beginning to occur within this concentration domain.

The luminescence emissions of 1 and 2 were also

sensitive to the presence of organic acids. For example,

incremental additions of CF₃CO₂H to both 1 and 2

resulted in a stepwise quenching of their respective

emissions and with a concomitant shift in the emission

maxima to lower energies (shown for 2 in Figure 9). The

spectra gradually decreased in intensity and energy over

several days, suggesting that kinetically controlled excited-

state aggregation processes were operative. The effect of

the weaker acids CH₃CO₂H and PhCO₂H on the lumi-

nescence of 2 were also investigated. The luminescence

of 9.8 × 10^-5M solutions of 2 in 1:1 CH₃CO₂H/CH₂Cl₂

and in 0.1 M PhCO₂H/CH₂Cl₂was partially quenched and

shifted to lower energy by 74 and 8 nm at 530 and 464

nm, respectively, upon excitation at 318 nm. Interest-

ingly, the fluorescence of 9.8 × 10^-5M solutions of 2 were

completely quenched in the presence of aromatic nitro

compounds such as nitrobenzene at a concentration of

0.1 M and 2,4,7-trinitrofluoren-9-one (TNF) at a ratio of

10:1 TNF/2. The latter result suggests the possibility that

2 may be able to participate in π-π interactions with

nitro-aromatics.

Spectroscopic Properties and Luminescence Cat-

ion Sensing by 3. The UV-vis spectrum of 3 in CH₂Cl₂

was rather unusual, exhibiting seven absorbances in-

cluding a particularly intense and sharp band at 288 nm

which were invariant in energy and shape below [3] )

2.7 × 10^-5M, showing that aggregation is not occurring

in dilute solution (Figure 10). Cycle 3 is also a fluorescent

chromophore, CH₂Cl₂solutions affording a green emis-

sion upon exposure to UV light. The fluorescence emis-

sion spectrum of 3 comprised three bands at 474, 494,

and 524 nm, which did not change in shape and energy

below 3.3 × 10^-5M, showing that excited-state aggrega-

(33) For a recent overview on fluorescent molecular sensors for

cation recognition, see: Valeur, B.; Leray, I. Coord. Chem. Revs. 2000,

205, 3.

(34) The metal chlorides and complexes used in the study were

CrCl₃‚6H₂O, FeCl₂, CoCl₂‚6H₂O, NiCl₂‚6H₂O, PdCl₂(MeCN)₂, PtCl₂-

(MeCN)₂, [Cu(MeCN)₄]BF₄, and AuCl(THT). All remaining cations

investigated were in the form of their anhydrous triflates. With the

exception of PdCl₂(MeCN)₂, [Cu(MeCN)₄]BF₄, and AuCl(THT), all stock

solutions were prepared in MeOH. The chromium, iron, cobalt and

nickel chlorides were each dissolved in a drop of distilled water prior

to the preparation of the standard solutions in methanol to ensure

complete solubility. For the same reason, the palladium and platinum

complexes were initially dissolved in 1 mL of warm acetonitrile, and

in the former case diluted to the required volume with CH₂Cl₂. The

AuCl(THT) solution was prepared in CH₂Cl₂and the [Cu(MeCN)₄]BF₄

solution in MeCN. The Hg(CF₃SO₃)₂was prepared from the reaction

between HgO and (CF₃SO₂)₂O.^14cThe Cu^II, Ag^I, and Tl^Itriflates used

were g 99.9% purity.

4944 J. Org. Chem., Vol. 70, No. 13, 2005

Nitrogen Heterocyclic Carbon-Rich Materials

TABLE 1. Coordination Preferences of Cycles L toward

Metal Ions in Dilute Solution Determined by UV-vis

Spectrophotometry

L

[L],^amol L^-1L/Mⁿ⁺

L/Mⁿ⁺coordination preferences

3

4

5

6

7

8

5.4 × 10^{-6 a}

6.6 × 10^{-6 b}

1.1 × 10^{-5 b}

7.3 × 10^{-6 b}

8.6 × 10^{-6 a}

9.6 × 10^{-6 c}

1:3

1:1

Pd^II

Co^II= Ni^II> Cu^II= Zn^II

Cu^II= Ag^I

1:1.5 Cu^II= Ag^I> Pd^II> Tl^I> Hg^II

1:4

Pd^II> Co^II= Ni^II= Ag^I> Fe^II= Hg^II

Pd^II. Ni^II> Co^II> Ag^I> Hg^II

^aThe spectrophotometric measurements were performed in the

following solvent mixtures: (a) 10% MeOH/CH₂Cl₂; (b) 33% CHCl₃/

MeOH; (c) 10% MeOH/CHCl₃. See refs 14a,c,l,n.

sites.³⁶The metal ion complexation behavior of 3 and 4-8

are summarized and compared in Table 1 above.

The spectroscopic metal ion binding studies were

conducted in dilute solutions where metal coordination

interactions may be expected to be very weak. On the

other hand, 3 would be expected to exhibit a richer

complexation chemistry under more concentrated condi-

tions. In order therefore to obtain an initial assessment

of the potential of 3 to form coordination polymers, a 1:4

mixture of 3/AgBF₄was prepared by adding a solution

of 3 in CH₂Cl₂(1 mL; [3] ) 4.4 × 10^-3M) to a solution

AgBF₄in MeCN (1 mL). Precipitation of a pale yellow

solid immediately ensued upon admixture of the reac-

tants and was completed by gentle heating. The isolated

solid was insoluble in all the usual laboratory solvents,

a property characteristic of cross-linked coordination

polymers, which severely hampered its characterization.

However, treatment of the solid with hot aqueous KCN

resulted in regeneration of the free ligand providing

further evidence that coordination of Ag⁺to 3 had

occurred.³⁷

FIGURE 11. UV-vis spectra of 5.4 × 10^-6M solutions of 3

in 10% MeOH/CH₂Cl₂titrated with incremental additions of

Hg(CF₃SO₃)₂, where the 3/Hg^IIratios are respectively 1:5, 1:10,

1:15, 1:20, 1:30, 1:50 (s), and 1:500 (- ‚ ‚). The spectra were

recorded 40 h after solution preparation at 25 °C.

sion spectra of the above 3/CF₃CO₂H and all of the 1:3

3/Mⁿ⁺solutions were then recorded. Of all cations

studied, only Pd^IIand protonation³⁵caused quenching of

the free ligand fluorescence. All other metals investigated

afforded zero changes in the emissions of the macrocycle.

The detection limit for Pd^IIwas estimated to be [Pd^II] )

1 × 10^-6M. The above results therefore demonstrate that

3 functions as a highly selective fluorescence quenching

sensor for Pd^II.

The fact that 3 possesses exotopic nitrogens suggests

that it would exhibit similar metal ion binding behavior

to the structurally related cycles 7 and 8 which coordinate

Co^II, Ni^II, Ag^I, and Hg^IIas well Pd^IIin dilute solution.

However, no evidence for the complexation of 3 to Mⁿ⁺

)

Thermal Behavior of Macrocycles and Precur-

sors. Some dehydrobenzoannulenes and related carbon-

rich structures have been reported to function as high

Co^II, Ni^II, Ag^I, and Hg^IIwas observed for 1:3 ratios of

3/Mⁿ⁺where [3] ) 5.4 × 10^-6M. Interestingly, 3 was

found to bind Hg^IIwhen the metal salt was slightly more

concentrated, i.e., at 3/Hg^IIratios g1:5 with [3] ) 5.4 ×

10^-6M in 10% MeOH/CH₂Cl₂(Figure 11). The Hg^II

binding also caused a quenching of the free ligand

fluorescence. Cycles 7 and 8 signal the presence of Co^II,

Ni^II, and Ag^Iin dilute solution by forming insoluble

coordination polymer precipitates. The reason 3 fails to

bind to Co^II, Ni^II, Ag^Iunder dilute conditions may

originate from the fact that it has less coordination sites

compared to 7 and 8 and may thus be unable to form

coordination polymers with sufficient cross-linking for

precipitation. In contrast, ligands 4-6 display rather

different metal ion-binding preferences dictated by their

respectively endo- and exotopic bidentate coordination

(36) Cycles 4-6 incorporate bidentate complexation sites that would

be expected to prefer metal ions with for example octahedral coordina-

tion geometries. This situation is found for 4, which shows strong

binding affinities for the ions Co^II, Ni^II, Cu^IIand Zn^IIin dilute solution.

However, 5 and 6 deviate from this expected behavior due to the

presence of the hindering alkyne substituents in the 6,6′-positions of

the 2,2′-bypyridines. Cycle 5 binds only Cu^IIand Ag^I, presumably

because it is a relatively rigid structure in which the 2,2′-bipyridine

nitrogens are constrained in a transoid arrangement thereby discour-

aging metal ion coordination. Ligand 6 is more flexible and able to

bind metals into a loose tetrahedral coordination pocket. It is also

probable that the Cu^II, Ag^I, Pd^II, and Hg^II, which are documented to

form coordination interactions with alkynes, may be binding to the

alkyne substituents of the 2,2′-bipyridines of 5 and 6.^14l,14n

(37) Dehydrotribenzo[12]annulene, the hydrocarbon analogue of 3,

has been described to form an [L₂Ag]⁺complex with AgCF₃SO₃, in

which a silver ion is sandwiched between the triangular cavities of

two dehydrotribenzo[12]annulene molecules, via coordination to the

alkynes. See: (a) ref 6c. (b) Ferrara, J. D.; Djebli, A.; Tessier-Youngs,

C.; Youngs, W. J. J. Am. Chem. Soc. 1988, 110, 647. The complexation

of 3 by Ag^Imay therefore be expected to yield structurally more

complex products as coordination to both the pyridine nitrogens and

the alkynes is possible. However a comparison of the infrared spectra

of 3 with the product of the reaction between 3 and AgBF₄, recorded

as polychlorotrifluoroethylene mulls, showed only minor differences

in the alkyne stretching absorbances. In the 3/AgBF₄reaction product,

the latter absorbance appeared as a weak and broadened band at 2226

cm^-1, compared to two weak bands at 2227 and 2212 cm^-1in 3,

indicating negligible interactions between the alkyne units and Ag^I.

However, the three strong bands due to the pyridyl CC and CN

stretches at 1591, 1494, and 1410 cm^-1in the infrared spectrum of

(35) A 1:3 3/Pd^IIratio ([Pd^II] ) 1.62 × 10^-5M) was sufficient to

quench the luminescence of 3, whereas

a much greater proton

concentration ([CF₃COOH] ) 0.1 M) was required to quench the

luminescence of 3 (where [3] ) 5.4 × 10^-6M) suggesting that the Pd^II

is binding more strongly to 3 than protons. It may also be noted that

all spectra of 1-3 in the presence of CF₃COOH were recorded in pure

CH₂Cl₂. In 10% MeOH/CH₂Cl₂, the spectroscopic effects of protonation

by CF₃COOH are further reduced due to preferential solvation of the

acid by MeOH. Proton-controllable fluorescence phenomena have been

reported for oligomeric linear, branched, and cyclic conjugated organic

scaffolds incorporating nitrogen-donor heterocycles; see: (a) refs

[14a,c,k,l]; (b) Martin, R. E.; Wytko, J. A.; Diederich, F.; Boudon, C.;

Gisselbrecht, J.-P.; Gross, M. Helv. Chim. Acta 1999, 82, 1470. (c)

Pabst, G. R.; Pfu¨ller, O. C.; Sauer, J. Tetrahedron 1999, 55, 5047. (d)

Yamamoto, T.; Sugiyama, K.; Kushida, T.; Inoue, T.; Kanbara, T. J.

Am. Chem. Soc. 1996, 118, 3930.

the 3/AgBF₄reaction product were shifted by 12, 5, and 14 cm^-1

,

respectively, to higher energy with respect to 3, suggestive of metal

ion interaction with the pyridines.

J. Org. Chem, Vol. 70, No. 13, 2005 4945

Baxter and Dali-Youcef

1, 2, and 3, which constitute three structurally different

members of a new class of dehydroannulenes that

incorporate nitrogen heterocyclic rings. Cycles 1-3 pos-

sess a unique combination of features such as cyclic ortho-

conjugation, sites for the coordination of metal ions,

chirality in the case of 1-2, and in particular, they were

all discovered to function as fluorescent chromophores.

These characteristics collectively support the conclusion

that they represent structurally unique ligand scaffolds

which should possess intriguing physicochemical proper-

ties. Investigations into the metal-binding profile of 3 in

dilute solution demonstrated that the macrocycle func-

tions as highly sensitive and specific sensor for Pd^IIions,

exhibiting a fluorescence quenching output response for

this metal ion. Under conditions of increased concentra-

tion, ligand 3 was found to form coordination polymers

with metal ions such as Ag^I. Interestingly, 3 also under-

goes proton triggered fluorescence quenching, in similar-

ity to 4-8.^14a,c,l,n

FIGURE 12. TGA thermal decomposition profiles of 2-3 mg

samples of cycles 1, 2, 7, and 8, heated at a rate of 10 °C/min

under nitrogen. The decomposition temperature ranges are

shown in parentheses for each compound.

In conclusion, cycles 1-3 and their metal complexes

may be promising candidates for the development of for

example, novel ion sensors, hybrid organic-inorganic

coordination networks^13a-d,26a-gand materials with pho-

tonics applications.^38a-cFurthermore, the o-diethynylpy-

ridine building blocks and macrocycle precursors de-

scribed above may be expected to participate in topo-

chemical and Bergman type polymerizations to afford

novel nitrogen heterocyclic carbon rich conjugated

polymers.^17b,39a,bReports on work supportive of the above

expectations will follow, along with the preparation and

properties of structurally more elaborate nitrogen het-

erocyclic carbon-rich materials and their metal com-

plexes, as well as the utilization of these materials for

the fabrication light emitting diodes (LEDs).

energy materials, igniting explosively when heated, to

afford in particular cases, small quantities of buckytubes

and buckyonions among other unidentified carbonaceous

reaction products.^10a-dCycles 7 and 8 were also discov-

ered to ignite explosively upon rapid heating above

particular temperature thresholds to yield black carbon

solids.^14a,cInitial investigations into the thermal behavior

of the solids described in the above work revealed that

1, 2, 15, 23, and 29 also explosively ignited with

concomitant soot formation at specific temperatures. In

the case of 1 and 23, the faint odor of HCN gas was

detectable directly after ignition, indicating that the

reaction mechanism involves the breakdown of the py-

ridine rings with the expulsion of nitrogen as HCN.

Thermogravimetric analyses performed upon the cycles

1, 2, 7, and 8 are shown in Figure 12. The TGA

decomposition temperature ranges are 5-20 °C lower

than those observed using a melting point apparatus (see

the Experimental Section), which may in part originate

from the relatively slow thermal heat transfer properties

inherent in the latter equipment. The large mass losses

observed during the TGA measurements reflected the

ferocity of the decompositions, which involved ejection

of a portion of the sample from the crucible. The TGA

heating was continued up to 900 °C for cycle 2 to assess

the stability of the residue which remained after the

explosive decomposition. In this case, no further changes

in mass occurred until 560 °C, whereupon a relatively

small and steady loss in mass was maintained up to the

heating limit of 900 °C.

Experimental Section

General Synthetic Procedures. Variations in the follow-

ing general procedures A-F were necessary in some cases in

order to achieve optimal product yields and purities. These

details are provided below when necessary for the particular

products concerned.

(A) Sonogashira-Type Heterocouplings. To the respec-

tive iodopyridine in the presence of a catalytic amount of PdCl₂-

(PPh₃)₂or [PdCl₂(dppf)]‚CH₂Cl₂under an atmosphere of argon

was added by syringe Et₃N or toluene as solvent, followed by

the appropriate alkyne reactant. After the mixture was stirred

for 0.2 h, a solution of CuI in Et₃N was syringed into the

reaction and stirring continued for 5-7 days at ambient

temperature in the absence of light. A gray, brown, or yellow

precipitate slowly formed in all cases, visually indicating the

progress of the reaction. All solvent was then removed under

reduced pressure on a water bath at 70 °C and the residue

extracted with 5 × 30 mL of pentane. The combined extracts

were gravity filtered and the solvent removed under reduced

pressure on a water bath at ambient temperature. The crude

product was purified by flash chromatography on silica, eluting

In contrast to the explosive decompositions described

above, slow heating of the former compounds from below

their respective ignition temperature thresholds, resulted

in the crystals gradually becoming glossy black in ap-

pearance, but with little visible change in crystal mor-

phology. These preliminary results suggest that o-dieth-

ynylpyridine-based materials may also serve as potential

candidates for the generation of carbon-rich network

polymers, either via a high energy explosive route, or by

lower energy thermal curing. More detailed investiga-

tions into these possibilities are currently underway.

(38) The electro- and photoactive properties of structurally simple

metal-complexed linear conjugated ligands have been widely studied

in order to assess their potentiality for the construction of molecular

level photonic devices. For reviews in this area, see: (a) De Cola, L.;

Belser, P. In Electron transfer in chemistry; Balzani, V., Ed.; Wiley

VCH: Weinheim, Germany, 2001; Vol. 5, pp 97-136. (b) Barigelletti,

F.; Flamigni, L. Chem. Soc. Rev. 2000, 29, 1. (c) Balzani, V.; Juris, A.;

Venturi, M.; Campagna, S.; Serroni, S. Chem. Rev. 1996, 96, 759.

(39) (a) John, J. A.; Tour, J. M. Tetrahedron 1997, 15515. (b)

Baldwin, K. P.; Matzger, A. J.; Scheiman, D. A.; Tessier, C. A.;

Vollhardt, K. P. C.; Youngs, W. J. Synlett 1995, 1215.

Conclusion

The above work discloses the successful synthesis and

spectroscopic characterization of dehydropyridoannulenes

4946 J. Org. Chem., Vol. 70, No. 13, 2005

Nitrogen Heterocyclic Carbon-Rich Materials

with CH₂Cl₂. Further purification was achieved by dissolving

the product in 20-30 mL of MeOH and stirring with NORIT

A decolorizing charcoal (0.05-0.25 g), gravity filtering, and

removal of the solvent under reduced pressure on a water bath

at 50 °C. The latter procedure was repeated using similar

quantities of NORIT A and powdered anhydrous Na₂SO₄(1-3

g) in 30-60 mL pentane and removal of the solvent under

reduced pressure at ambient temperature. The product thus

obtained was finally dried under dynamic vacuum at 0.01

mmHg.

was equipped with a vacuum/argon inlet adaptor, alcohol

thermometer, rubber septum, and magnetic stirrer ovoid. The

flask was then evacuated and back-filled with argon four times

and Et₂O (120-180 mL) added by syringe. The stirred solution

was subsequently cooled to an internal temperature of -78

°C using a CO₂/acetone bath. The appropriate quantity of

n-BuLi (1.6 M in hexanes) was added dropwise by syringe at

a rate which maintained the reaction temperature between

-78 and -70 °C. The reaction solution was then stirred at

-78 °C for 1.5 h. Et₂O (10-30 mL) was syringed into a dried,

argon-filled Schlenk tube containing diiodoethane and the

mixture stirred until all of the diiodoethane dissolved. The

diiodoethane solution was then added dropwise by syringe to

the lithioarene reaction mixture at a rate which maintained

the internal temperature between -78 and -70 °C. The

reaction was stirred at -78 °C for a further 3 h and then

allowed to warm to ambient temperature with continued

stirring overnight. The reaction solution was extracted with

distilled water (3 × 180 mL), the organic layer separated, dried

(anhydrous Na₂SO₄), filtered, and the Et₂O removed by distil-

lation at atmospheric pressure on a water bath at 50 °C. The

remaining brown oil was further dried under vacuum (0.05

mmHg) and worked up as described for each compound below.

(F) Macrocyclizations to 1 and 2. In a well-ventilated

hood, [Cu₂(OAc)₄]‚nH₂O (n ) 0, 2) was dissolved in warm

pyridine (500-600 mL), and the stirred solution was bubbled

with argon for 1.5 h, during which time it cooled to ambient

temperature. A solution of the dialkyne in pyridine (34) or

toluene (39) was then slowly added dropwise over 3-7 h to

the [Cu₂(OAc)₄]‚nH₂O solution, with continued stirring and

argon bubbling. After the addition of the dialkyne was

complete, the reaction was stirred under a static atmosphere

of argon, at ambient temperature and in the absence of light

for 21-25 d. All solvent was then removed under reduced

pressure on a water bath, and the residue was further dried

at 70 °C under vacuum for 0.5 h. Distilled water (300 mL) and

excess ice were added, and the mixture was vigorously stirred.

Excess solid KCN was then added in 0.2 g portions with

continued stirring until no further visible change occurred, at

which point the mixture appeared as a brown suspension.

Further workup and purification methods are detailed sepa-

rately for each product below.

(B) Selective TMS Deprotection. To a stirred solution

of the trimethylsilylethynyl substrate in MeOH was added the

appropriate quantity of finely powdered K₂CO₃and the

suspension stirred at ambient temperature in the absence of

light for 17-36 h. The reaction solution was then reduced in

volume to about 3 mL under reduced pressure on a water bath

at ambient temperature and the concentrate partitioned

between water (100 mL) and pentane (40 mL). The aqueous

layer was extracted with a further portion of pentane (30 mL),

the combined organic layers were extracted with water (5 ×

30 mL) and dried (anhydrous Na₂SO₄), filtered under gravity,

and the solvent was removed under reduced pressure on a

water bath at ambient temperature. The product was initially

purified by flash chromatography on silica with CH₂Cl₂as

eluant. The solvent was removed from the fractions containing

the product, under reduced pressure on a water bath at e50

°C, to minimize any possible thermal degradation. Further

purification was achieved by dissolving the product in 30-70

mL of MeOH and stirring with NORIT A decolorizing charcoal

(0.05-0.25 g), gravity filtering, and removal of the solvent

under reduced pressure on a water bath at ambient temper-

ature. The latter procedure was repeated using similar quanti-

ties of NORIT A and powdered anhydrous Na₂SO₄(1-3 g) in

20-50 mL of pentane and removal of the solvent under

reduced pressure at ambient temperature. The product thus

obtained was finally dried under dynamic vacuum at 0.01

mmHg.

(C) Hay Ethyne Homocoupling Reactions. To a solution

of the arylethyne in pyridine was added a solution of the CuCl

or CuI catalyst in pyridine (1-2 mL) and the stirred reaction

bubbled with oxygen gas for 1.5 h. During this time, a color

change from yellow to green usually occurred. The reaction

flask was tightly closed and the solution vigorously stirred in

the absence of light until TLC sampling indicated complete

consumption of the starting alkyne (18 h to 2 d). The reaction

was then poured onto a mixture of brine and water (3:1, 300

mL) and extracted with pentane (4 × 50 mL). The combined

pentane extracts were washed with water (3 × 200 mL), dried

(anhydrous Na₂SO₄), and filtered, and the solvent was removed

under reduced pressure on a water bath at ambient temper-

ature. The residue was further dried under dynamic vacuum

over 16 h, and MeOH or MeCN (4-6 mL) was added to

complete the crystallization of the product. The mixture was

then triturated and briefly ultrasonicated, filtered under

vacuum, and washed with a few milliliters of MeOH or MeCN.

Unless otherwise stated, the product was further purified by

recrystallization from MeOH (14-20 mL) and dried under

dynamic vacuum at 0.01 mmHg.

3-Triisopropylsilylethynyl-4-trimethylsilylethynyl-

pyridine (12). Compound 12 (1.414 g, 96%) was obtained as

a pale yellow oil from the reaction between 11 (1.245 g, 4.13

× 10^-3mol), PdCl₂(PPh₃)₂(0.050 g, 7.12 × 10^-5mol), and

TIPSA (0.806 g, 4.42 × 10^-3mol) in Et₃N (15 mL) and a

solution of CuI (0.040 g, 2.10 × 10^-4mol) in Et₃N (4 mL),

according to the general procedure A above. ¹H NMR (CDCl₃,

3

400 MHz, 25 °C): δ ) 8.675 (s, 1H; H2), 8.426 (d, J(6,5) )

5.1 Hz, 1H; H6), 7.294 (d, ³J(5,6) ) 5.1 Hz, 1H; H5), 1.152 (s,

21H; CH(CH₃)₂), 0.252 ppm (s, 9H; Si(CH₃)₃). ¹³C NMR (CDCl₃,

100.6 MHz, 25 °C): δ ) 153.4, 147.8, 132.9, 125.8, 121.8, 103.9

(-Ct), 102.0 (-Ct), 100.6 (-Ct), 98.7 (-Ct), 18.7 (CH-

(CH₃)₂), 11.2 (CH(CH₃)₂), -0.4 ppm Si(CH₃)₃). IR (thin film):

3036 (w), 2959 (s), 2943 (s), 2865 (s), 2164 (m) (CtC), 1574

(s), 1476 (s), 1463 (s), 1398 (s), 1250 (s), 874 (s), 845 (s), 679

cm^-1(s). FABMS: m/z 356 (100) [M⁺+ H]. HRMS (FAB, [M⁺

+ H]): calcd for C₂₁H₃₄NSi₂356.2230, found 356.2247.

(D) Fluoride-Mediated Desilylations. To a stirred solu-

tion of the trialkylsilylalkyne in THF (12-40 mL) was added

dropwise a small quantity of distilled water (1-14 drops)

followed by the appropriate quantity of the [(n-Bu)₄N]F (1.0

M in THF) solution, and stirring was continued at ambient

temperature in the absence of light until TLC sampling

indicated complete deprotection (14 h to 1.5 d). All solvent was

removed under reduced pressure at ambient temperature,

distilled water (30-50 mL) added, and the mixture filtered

under vacuum. The residue collected was washed with excess

distilled water and air-dried to afford a tacky solid which was

purified as described individually for each compound below.

3-Triisopropylsilylethynyl-4-ethynylpyridine (13). Com-

pound 13 (2.867 g, 90%) was obtained as a soft cream

crystalline solid upon the reaction between 12 (4.000 g, 1.12

× 10^-2mol) and K₂CO₃(0.780 g, 5.64 × 10^-3mol) in MeOH

(125 mL) for 1.5 d according to the general deprotection

procedure B. ¹H NMR (CDCl₃, 500 MHz, 25 °C): δ ) 8.706 (s,

3

1H; H2), 8.471 (d, J(6,5) ) 5.2 Hz, 1H; H6), 7.328 (d, J(5,6)

) 4.7 Hz, 1H; H5), 3.471 (s, 1H; -CtCH), 1.152 ppm (s, 21H;

CH(CH₃)₂). ¹³C NMR (CDCl₃, 125.8 MHz, 25 °C): δ ) 153.0,

148.0, 132.4, 125.6, 122.7, 101.6 (-Ct), 99.4 (-Ct), 85.5

(-Ct), 79.9 (-Ct), 18.6 (CH(CH₃)₂), 11.2 ppm (CH(CH₃)₂).

IR: 3151 (s) (H-Ct), 2937 (s), 2861 (s), 2165 (m) (CtC), 2104

(s) (CtC), 1580 (s), 1477 (s), 1461 (s), 1399 (s), 882 (s), 834

(E) Bromine/Iodine Metatheses. A dried 500 mL two-

necked round-bottomed flask charged with the aryl bromide

J. Org. Chem, Vol. 70, No. 13, 2005 4947

Baxter and Dali-Youcef

(s), 756 (s), 676 cm^-1(s). FABMS: m/z 284 (100) [M⁺+ H],

240 (9) [M⁺- {CH₂(CH₃)₂}], 212 (4) [M⁺- {CH₂(CH₃)₂} -

2{CH₂}], 198 (6) [M⁺- {CH₂(CH₃)₂} - 3{CH₂}], 184 (9) [M⁺

- {CH₂(CH₃)₂} - 4{CH₂}], 170 (10) [M⁺- {CH₂(CH₃)₂} -

5{CH₂}]. HRMS (FAB, [M⁺+ H]): calcd for C₁₈H₂₆NSi

284.1835, found 284.1825.

(CtC), 1573 (s), 1460 (m), 1396 (s), 1377 (m), 1080 (m), 1016

(s), 832 (s), 785 cm^-1(m). EIMS: m/z 229 (100) [M⁺], 102 (29)

[M⁺- I]. HRMS (FAB, [M⁺+ H]): calcd for C₇H₅NI 229.9467,

found 229.9468.

1,4-Bis(4-(3-iodo)pyridyl)buta-1,3-diyne (17). A solution

of 16 (0.256 g, 1.12 × 10^-3mol) and CuCl (0.019 g, 1.92 ×

10^-4mol) was stirred in oxygenated pyridine (18 mL) for 24 h

according to the general coupling procedure C. The solvent was

distilled off under vacuum at ambient temperature, and a

solution of KCN (1 g) in water (20 mL) added to the residue.

The mixture was stirred for 1 h and the suspended solid

isolated by filtration under vacuum, washed with excess

distilled water, and air-dried. The product was further purified

by recrystallization from boiling heptane (20 mL), air-drying,

and drying under dynamic vacuum to afford 17 (0.202 g, 79%)

as colorless needles which rapidly become pink upon exposure

to light. (Gradual color darkening and decomposition to a black

residue occurs upon slow heating from 185 to 235 °C, with no

further visible changes up to 310 °C.) ¹H NMR (CDCl₃, 500

MHz, 25 °C): δ ) 9.006 (s, 2H; H2), 8.557 (d, ³J(6,5) ) 4.9 Hz,

1,4-Bis(4-(3-triisopropylsilylethynyl)pyridyl)buta-1,3-

diyne (14). Compound 14 (0.436 g, 86%) was obtained as

colorless needles from the reaction between 13 (0.510 g, 1.80

× 10^-3mol) and CuI (0.024 g, 1.26 × 10^-4mol) in oxygenated

pyridine (45 mL), according to the general coupling procedure

C. During workup, the crude 14 isolated from the pentane

1

extraction was triturated in MeOH. Mp: 136.0-137.0 °C. H

NMR (CDCl₃, 500 MHz, 25 °C): δ ) 8.733 (s, 2H; H2), 8.510

3

(d, J(6,5) ) 5.2 Hz, 2H; H6), 7.313 (d, J(5,6) ) 5.1 Hz, 2H;

H5), 1.165 ppm (m, 42H; CH(CH₃)₂). ¹³C NMR (CDCl₃, 100.6

MHz, 25 °C): δ ) 152.9, 148.0, 131.7, 125.3, 122.9, 101.2

(-Ct), 100.5 (-Ct), 80.9 (-Ct), 80.2 (-Ct), 18.6 (CH(CH₃)₂),

11.2 ppm (CH(CH₃)₂). IR: 2943 (s), 2865 (s), 2155 (m) (CtC),

1570 (s), 1471 (s), 1463 (m), 1396 (m), 996 (m), 882 (m), 833

(m), 757 (s), 673 cm^-1(s). FABMS: m/z 565 (100) [M⁺+ H];

521 (5) [M⁺- {CH₂(CH₃)₂}]. HRMS (FAB, [M⁺+ H]): calcd

for C₃₆H₄₉N₂Si₂565.3434, found 565.3419. Anal. Calcd for

C₃₆H₄₈N₂Si₂: C, 76.53; H, 8.56; N, 4.96. Found: C, 76.72; H,

8.70; N, 4.90.

3

2H; H6), 7.426 ppm (d, J(5,6) ) 4.9 Hz, 2H; H5). ¹³C NMR

(CDCl₃, 125.8 MHz, 25 °C): δ ) 157.3, 148.4, 135.5, 127.3,

98.8 (C-I), 83.2 (-Ct), 80.2 ppm (-Ct). IR: 2158 (CtC) (vw),

1564 (s), 1457 (s), 1393 (m), 1276 (m), 1078 (s), 1012 (s), 831

(s), 789 (s), 560 (m), 482 cm^-1(m). FABMS: m/z 457 (100) [M⁺

+ H]. Anal. Calcd for C₁₄H₆I₂N₂: C, 36.87; H, 1.33; N, 6.14.

Found: C, 36.55; H, 1.39; N, 6.17.

1,4-Bis(4-(3-ethynyl)pyridyl)buta-1,3-diyne (15). A solu-

tion of 14 (0.356 g, 6.30 × 10^-4mol), 4 drops of distilled water,

and a 1.0 M solution of [(n-Bu)₄N]F in THF (2 mL, 2 × 10^-3

mol) in THF (30 mL) were stirred for 24 h and worked up as

described in the general procedure D. The crude 15 was

suspended in cold MeOH (3 mL), filtered under vacuum,

washed with MeOH (3 × 1 mL) and Et₂O (2 mL), and air-

dried. The solid was then chromatographed on silica, gradient

eluting successively with CH₂Cl₂, CH₂Cl₂/1%MeOH, and CH₂-

Cl₂/2%MeOH. Further purification was achieved by briefly

stirring in CH₂Cl₂with NORIT A (0.06 g), filtering under

gravity, and removal of the solvent under reduced pressure

at ambient temperature. The remaining solid was suspended

in Et₂O (4 mL), filtered under vacuum, washed with cold Et₂O

(2 × 1 mL), and air-dried to afford 15 (0.121 g, 76%) as off-

white fibrous needles. (Upon slow heating from below 167.8

°C, the crystals become glossy black in appearance, with no

further visible change up to 310 °C. When 15 is rapidly heated,

it ignites explosively at g167.8 °C to yield a black residue.)

¹H NMR (CDCl₃, 400 MHz, 25 °C): δ ) 8.769 (s, 2H; H2), 8.564

3-Bromo-4-triisopropylsilylethynylpyridine (18). Using

general procedure A, a mixture of 9 (4.003 g, 1.41 × 10^-2mol),

PdCl₂(PPh₃)₂(0.110 g, 1.57 × 10^-4mol), and TIPSA (2.627 g,

1.44 × 10^-2mol) in Et₃N (70 mL) and a solution of CuI (0.100

g, 5.25 × 10^-4mol) in Et₃N (5 mL) was stirred at ambient

temperature for 7 d. After isolation from the pentane extrac-

tion, the crude product oil was flash chromatographed on silica,

eluting with Et₂O/hexane (1:4), and distilled under vacuum

(122 °C/0.005 mmHg) to afford 18 (4.130 g, 87%) as a colorless

oil. ¹H NMR (CDCl₃, 400 MHz, 25 °C): δ ) 8.745 (s, 1H; H2),

8.452 (d, ³J(6,5) ) 5.0 Hz, 1H; H6), 7.352 (d, ³J(5,6) ) 5.0 Hz,

1H; H5), 1.152 ppm (m, 21H; CH(CH₃)₂). ¹³C NMR (CDCl₃,

100.6 MHz, 25 °C): δ ) 151.7, 147.6, 133.0, 127.1, 123.2, 102.6

(-Ct), 102.0 (-Ct), 18.6 (CH(CH₃)₂), 11.2 ppm (CH(CH₃)₂).

IR (thin film): 3039 (w), 2943 (s), 2866 (s), 2164 (w) (CtC),

1571 (s), 1465 (s), 1396 (s), 1276 (s), 1086 (s), 1020 (s), 997 (s),

883 (s), 842 (s), 705 (s), 679 (s), 663 cm^-1(s). FABMS: m/z

340 (100) [M⁺+ H]; 296 (12) [M⁺- {CH₂(CH₃)₂}]. HRMS

(FAB, [M⁺+ H]): calcd for C₁₆H₂₅BrNSi 338.0940, found

338.0941.

3

(d, J(6,5) ) 5.0 Hz, 2H; H6), 7.402 (d, J(5,6) ) 5.0 Hz, 2H;

H5), 3.519 ppm (s, 2H; -CtCH). ¹³C NMR (CDCl₃, 100.6 MHz,

65 °C): δ ) 153.4, 148.8, 132.0, 125.6, 121.6, 84.9 (-Ct), 80.8

(-Ct), 80.1 (-Ct), 78.8 ppm (-Ct). IR: 3216 (s) (H-Ct),

3203 (s) (H-Ct), 2107 (s) (CtC), 1574 (s), 1474 (s), 1398 (s),

1180 (m), 828 (s), 738 (s), 695 (m), 578 cm^-1(m). FABMS: m/z

253 (100) [M⁺+ H]; HRMS (FAB, [M⁺+ H]): calcd for C₁₈H₉N₂

253.0766, found 253.0765. Anal. Calcd for C₁₈H₈N₂: C, 85.70;

H, 3.20; N, 11.10. Found: C, 85.44; H, 3.17; N, 11.13.

3-Iodo-4-triisopropylsilylethynylpyridine (19). A solu-

tion of 18 (2.600 g, 7.68 × 10^-3mol) in Et₂O (120 mL) was

lithiated with 1.6 M n-BuLi in hexanes (5 mL, 8.00 × 10^-3

mol) and the resulting pyridyllithium quenched with a solution

of diiodoethane (4.40 g, 1.56 × 10^-2mol) in Et₂O (10 mL) to

give crude 19 as a yellow oil, after initial workup according to

the general procedure E above. The product was then column

chromatographed three times in succession on silica, eluting

with CH₂Cl₂, dissolved in pentane (10 mL), and gravity filtered

and the pentane removed under reduced pressure on a water

bath at ambient temperature to afford 19 (2.367 g, 80%) after

drying under dynamic vacuum (0.01 mmHg). ¹H NMR (CDCl₃,

3-Iodo-4-ethynylpyridine (16). A THF (18 mL) solution

of 11 (0.856 g, 2.84 × 10^-3mol), distilled water (1.5 mL), and

a 1.0 M solution of [(n-Bu)₄N]F in THF (3.0 mL, 3 × 10^-3mol)

were stirred for 14 h as described in the general procedure D.

The reaction solution was then diluted with water (60 mL)

and extracted with pentane (3 × 25 mL). The combined

pentane extracts were extracted with water (3 × 30 mL), and

the organic phase was dried (anhydrous MgSO₄), shaken with

NORIT A (0.15 g), and gravity filtered. All solvent was

removed from the filtrate under reduced pressure on a water

bath at ambient temperature and the remaining solid dried

under dynamic vacuum to afford 16 (0.590 g, 91%) as a cream

crystalline volatile solid, pure by ¹H and ¹³C NMR. Mp: 86.0-

87.0 °C. ¹H NMR (CDCl₃, 500 MHz, 25 °C): δ ) 8.974 (s, 1H;

H2), 8.504 (d, ³J(6,5) ) 4.9 Hz, 1H; H6), 7.377 (d, ³J(5,6) )

4.9 Hz, 1H; H5), 3.627 ppm (s, 1H; -CtCH). ¹³C NMR (CDCl₃,

125.8 MHz, 25 °C): δ ) 157.2, 148.3, 136.3, 127.2, 98.9 (C-I),

85.6 (-Ct), 82.7 ppm (-Ct). IR: 3153 (s) (H-Ct), 2097 (s)

3

400 MHz, 25 °C): δ ) 8.946 (s, 1H; H2), 8.463 (d, J(6,5) )

5.1 Hz, 1H; H6), 7.344 (d, ³J(5,6) ) 5.1 Hz, 1H; H5), 1.160

ppm (m, 21H; CH(CH₃)₂). ¹³C NMR (CDCl₃, 100.6 MHz, 25

°C): δ ) 157.0, 148.2, 137.4, 126.9, 105.3, 101.6, 99.2, 18.6

(CH(CH₃)₂), 11.2 ppm (CH(CH₃)₂). IR (thin film): 3034 (w),

2942 (s), 2864 (s), 2163 (w) (CtC), 1568 (s), 1460 (s), 1394 (s),

1273 (s), 1080 (s), 1012 (s), 883 (s), 841 (s), 694 (s), 679 (s),

664 cm^-1(s). FABMS: m/z 386 (100) [M⁺+ H], 342 (7) [M⁺

-

{CH₂(CH₃)₂}]. HRMS (FAB, [M⁺+ H]): calcd for C₁₆H₂₅INSi

386.0801, found 386.0802.

3-Trimethylsilylethynyl-4-triisopropylsilylethynyl-

pyridine (20). Using general procedure A, compound 20

(2.091 g, 96%) was obtained as a pale honey-colored oil from

4948 J. Org. Chem., Vol. 70, No. 13, 2005

Nitrogen Heterocyclic Carbon-Rich Materials

1

the reaction between 19 (2.362 g, 6.13 × 10^-3mol), PdCl₂-

(PPh₃)₂(0.052 g, 7.41 × 10^-5mol), and TMSA (0.765 g, 7.79 ×

10^-3mol) in Et₃N (24 mL) and a solution of CuI (0.050 g, 2.63

× 10^-4mol) in Et₃N (4 mL). After the chromatographic

purification, the product in some runs may be contaminated

with paramagnetic impurities. These may be removed by

shaking a CH₂Cl₂(30 mL) solution of the product with a

mixture of powdered ascorbic acid (1 g) and KCN (1 g) followed

microneedles, pure by H and ¹³C NMR. (Upon slow heating,

the crystals become glossy black in appearance between 175

and 185 °C, with no further visible change up to 310 °C. With

rapid heating, 23 ignites explosively at g189.0 °C to yield a

1

black residue.) H NMR (CDCl₃, 400 MHz, 25 °C): δ ) 8.792

(s, 2H; H2), 8.552 (d, ³J(6,5) ) 5.3 Hz, 2H; H6), 7.385 (d, ³J(5,6)

) 5.0 Hz, 2H; H5), 3.619 ppm (s, 2H; -CtCH). ¹³C NMR

(CDCl₃, 100.6 MHz, 25 °C): δ ) 153.5, 149.0, 133.2, 125.8,

120.9, 86.6 (-Ct), 79.9 (-Ct), 79.2 (-Ct), 78.7 ppm (-Ct).

IR: 3205 (s) (H-Ct), 2108 (s) (CtC), 1575 (s), 1530 (m), 1474

(m), 1401 (m), 835 (s), 752 (s), 741 (s), 721 (s), 576 cm^-1(m).

FABMS: m/z 253 (100) [M⁺+ H]. HRMS (FAB, [M⁺+ H]):

calcd for C₁₈H₉N₂253.0766, found 253.0766.

1

by gravity filtration. H NMR (CDCl₃, 500 MHz, 25 °C): δ )

3

8.684 (s, 1H; H2), 8.435 (d, J(6,5) ) 5.1 Hz, 1H; H6), 7.298

(d, ³J(5,6) ) 5.2 Hz, 1H; H5), 1.150 ppm (m, 21H; CH(CH₃)₂).

¹³C NMR (CDCl₃, 125.8 MHz, 25 °C): δ ) 153.4, 148.0, 133.1,

125.8, 121.7, 102.6 (-Ct), 101.8 (-Ct), 101.1 (-Ct), 100.2

(-Ct), 18.7 (CH(CH₃)₂), 11.2 (CH(CH₃)₂), -0.2 ppm (Si(CH₃)₃).

IR (thin film): 3036 (w), 2958 (s), 2943 (s), 2866 (s), 2165 (m)

(CtC), 1574 (s), 1475 (s), 1463 (s), 1398 (s), 1250 (s), 874 (s),

845 (s), 796 (s), 761 (s), 679 (s), 665 cm^-1(s). FABMS: m/z

356 (100) [M⁺+ H]. HRMS (FAB, [M⁺+ H]): calcd for C₂₁H₃₄-

NSi₂356.2230, found 356.2236.

2-Trimethylsilylethynyl-3-iodopyridine (25). A solution

of 24 (4.299 g, 1.69 × 10^-2mol) in Et₂O (180 mL) was lithiated

with 1.6 M n-BuLi in hexanes (11 mL, 1.76 × 10^-2mol) and

the resulting pyridyllithium quenched with a solution of

diiodoethane (6.70 g, 2.38 × 10^-2mol) in Et₂O (30 mL) to give

crude 25 as a brown oil, after initial workup according to

procedure E above. The product was then chromatographed

on silica, eluting initially with hexane until all the excess

diiodoethane had passed from the column, and then Et₂O/

hexane (1:4), to afford 25 (4.747 g, 93%) as a honey-colored oil

3-Ethynyl-4-triisopropylsilylethynylpyridine (21). The

reaction between 20 (0.451 g, 1.27 × 10^-3mol) and K₂CO₃

(0.090 g, 6.51 × 10^-4mol) in MeOH (35 mL) for 20 h afforded

21 (0.357 g, 99%) as a soft cream crystalline solid after workup,

using the general deprotection procedure B. ¹H NMR (CDCl₃,

1

after drying under dynamic vacuum (0.01 mmHg). H NMR

3

500 MHz, 25 °C): δ ) 8.704 (s, 1H; H2), 8.484 (d, J(6,5) )

(CDCl₃, 400 MHz, 25 °C): δ ) 8.510 (dd, ³J(6,5) ) 4.4 Hz,

5.0 Hz, 1H; H6), 7.321 (dd, ³J(5,6) ) 5.2 Hz, ⁵J(5,2) ) 0.8 Hz,

1H; H5), 3.377 (s, 1H; -CtCH), 1.146 ppm (s, 21H; CH(CH₃)₂).

¹³C NMR (CDCl₃, 125.8 MHz, 25 °C): δ ) 153.0, 148.5, 134.0,

125.4, 121.0, 102.1 (-Ct), 101.7 (-Ct), 84.0 (-Ct), 79.4

(-Ct), 18.6 (CH(CH₃)₂), 11.2 ppm (CH(CH₃)₂). IR (thin film):

3309 (s) (H-Ct), 3204 (m, broad) (H-Ct), 3038 (w), 2943 (s),

2865 (s), 2163 (w) (CtC), 2104 (w) (CtC), 1577 (s), 1476 (s),

1463 (s), 1399 (s), 883 (s), 857 (s), 835 (s), 764 (s), 680 (s), 666

cm^-1(s). FABMS: m/z 284 (100) [M⁺+ H], 240 (8) [M⁺- {CH₂-

(CH₃)₂}], 212 (5) [M⁺- {CH₂(CH₃)₂} - 2{CH₂}], 198 (7) [M⁺

- {CH₂(CH₃)₂} - 3{CH₂}], 184 (9) [M⁺- {CH₂(CH₃)₂} -

4{CH₂}], 170 (8) [M⁺- {CH₂(CH₃)₂} - 5{CH₂}]. HRMS (FAB,

[M⁺+ H]): calcd for C₁₈H₂₆NSi 284.1835, found 284.1829.

⁴J(6,4) ) 0.9 Hz, 1H; H6), 8.110 (dd, J(4,5) ) 8.2 Hz, J(4,6)

3

4

3

) 1.2 Hz, 1H; H4), 6.933 (dd, J(5,4) ) 8.2 Hz, J(5,6) ) 4.7

Hz, 1H; H5), 0.295 ppm (s, 9H; (Si(CH₃)₃)). ¹³C NMR (CDCl₃,

100.6 MHz, 25 °C): δ ) 148.7, 147.1, 145.9, 123.7, 104.6, 99.6,

98.6, -0.5 ppm (Si(CH₃)₃). IR (thin film): 2959 (s), 2167 (m)

(CtC), 1558 (s), 1407 (s), 1262 (s), 1250 (s), 1008 (s), 867 (s),

845 (s), 760 cm^-1(s). FABMS: m/z 302 (100) [M⁺+ H]. HRMS

(FAB, [M⁺+ H]): calcd for C₁₀H₁₃INSi 301.9862, found

301.9873.

2-Trimethylsilylethynyl-3-triisopropylsilylethynyl-

pyridine (26). Using general procedure A, a mixture of 25

(1.008 g, 3.35 × 10^-3mol), PdCl₂(PPh₃)₂(0.046 g, 6.55 × 10^-5

mol), and TIPSA (0.732 g, 4.01 × 10^-3mol) in Et₃N (15 mL)

and a solution of CuI (0.040 g, 2.10 × 10^-4mol) in Et₃N (5

mL) was heated in a bath at 75 °C for 3 d. The heating ensured

complete conversion of 25, as the reaction was found to be

rather sluggish when conducted at ambient temperature. The

crude product was chromatographed three times (silica/CH₂-

Cl₂) and further purified as described in general procedure A

above to yield 26 (0.760 g, 64%) as a pale yellow oil. ¹H NMR

(CDCl₃, 400 MHz, 25 °C): δ ) 8.483 (dd, ³J(6,5) ) 4.8 Hz,

1,4-Bis(3-(4-triisopropylsilylethynyl)pyridyl)buta-1,3-

diyne (22). Compound 22 was obtained from the reaction

between 21 (0.311 g, 1.10 × 10^-3mol) and CuCl (0.015 g, 1.52

× 10^-4mol) in oxygenated pyridine (29 mL), according to the

general coupling procedure C. However, an additional purifica-

tion step was necessary during workup. The crude 22 isolated

from the pentane extraction was triturated, washed with

MeCN as described in procedure C, and sublimed under

vacuum (120 °C/0.01 mmHg). The sublimate was then dis-

solved in boiling MeOH (30 mL), NORIT A (0.05 g) added, and

the mixture briefly stirred, gravity filtered, and left to stand

in the dark overnight, during which time the product crystal-

lized. A second crop of crystals were obtained upon partial

evaporation of the mother liquor to afford 22 (combined yield

of 0.211 g, 68%) as granular cream crystals. Mp: 131.5-132.0

°C. ¹H NMR (CDCl₃, 400 MHz, 25 °C): δ ) 8.699 (s, 2H; H2),

8.504 (d, ³J(6,5) ) 5.0 Hz, 2H; H6), 7.340 (d, ³J(5,6) ) 5.2 Hz,

2H; H5), 1.167 ppm (m, 42H; CH(CH₃)₂). ¹³C NMR (CDCl₃,

100.6 MHz, 25 °C): δ ) 153.1, 148.7, 134.5, 125.4, 120.9, 102.8

(-Ct), 101.8 (-Ct), 80.1 (-Ct), 79.0 (-Ct), 18.6 (CH(CH₃)₂),

11.2 ppm (CH(CH₃)₂). IR: 2942 (s), 2863 (s), 2164 (vw) (Ct

C), 1572 (s), 1470 (s), 1397 (s), 996 (s), 880 (s), 855 (s), 832 (s),

762 (m), 679 (s), 666 (s), 642 cm^-1(m). FABMS: m/z 565 (100)

[M⁺+ H]. HRMS (FAB, [M⁺+ H]): calcd for C₃₆H₄₉N₂Si₂

565.3434, found 565.3433. Anal. Calcd for C₃₆H₄₈N₂Si₂: C,

76.53; H, 8.56; N, 4.96. Found: C, 76.29; H, 8.62; N, 4.96.

⁴J(6,4) ) 1.6 Hz, 1H; H6), 7.748 (dd, J(4,5) ) 7.9 Hz, J(4,6)

3

4

3

) 1.8 Hz, 1H; H4), 7.165 (dd, J(5,4) ) 7.9 Hz, J(5,6) ) 4.7

Hz, 1H; H5), 1.151 (s, 21H; CH(CH₃)₂), 0.263 ppm (s, 9H; Si-

(CH₃)₃). ¹³C NMR (CDCl₃, 100.6 MHz, 25 °C): δ ) 148.6, 144.4,

140.1, 122.8, 122.1, 102.6 (-Ct), 102.4 (-Ct), 98.60 (-Ct),

98.56 (-Ct), 18.7 (CH(CH₃)₂), 11.2 (CH(CH₃)₂), -0.3 ppm (Si-

(CH₃)₃). IR (thin film): 3039 (w), 2957 (s), 2943 (s), 2865 (s),

2163 (m) (CtC), 2149 (m, sh) (CtC), 1463 (s), 1444 (s), 1415

(s), 1250 (s), 1177 (s), 1100 (s), 883 (s), 845 (s), 800 (s), 786 (s),

768 (s), 678 (s), 666 (s), 636 cm^-1(s). FABMS: m/z 356 (100)

[M⁺+ H], 312 (6) [M⁺- {CH₂(CH₃)₂}], 270 (9) [M⁺- {CH₂-

(CH₃)₂} - 3{CH₂}]. HRMS (FAB, [M⁺+ H]): calcd for C₂₁H₃₄-

NSi₂356.2230, found 356.2240.

2-Ethynyl-3-triisopropylsilylethynylpyridine (27). A

solution of 26 (0.657 g, 1.85 × 10^-3mol) in MeOH (40 mL)

with K₂CO₃(0.130 g, 9.41 × 10^-4mol) was stirred for 17 h at

ambient temperature. The reaction was worked up according

to the general deprotection procedure B with omission of the

chromatography step to afford 27 (0.519 g, 99%) as a very pale

yellow oil that crystallized at -30 °C and remelted upon

warming to ambient temperature. ¹H NMR (CDCl₃, 400 MHz,

1,4-Bis(3-(4-ethynyl)pyridyl)buta-1,3-diyne (23). A solu-

tion of 22 (0.128 g, 2.27 × 10^-4mol), 5 drops of distilled water,

and a 1.0 M solution of [(n-Bu)₄N]F in THF (0.6 mL, 6.0 ×

10^-4mol) in THF (12 mL) were stirred for 18 h and worked

up as described in the general procedure D. The crude 23 was

suspended in cold MeOH (3 mL), filtered under vacuum,

washed with MeOH (3 × 2 mL) and Et₂O (3 × 2 mL), and

air-dried to afford 23 (0.055 g, 96%) as cream-colored fibrous

3

4

25 °C): δ ) 8.50 (dd, J(6,5) ) 4.8 Hz, J(6,4) ) 1.6 Hz, 1H;

H6), 7.768 (dd, ³J(4,5) ) 7.9 Hz, ⁴J(4,6) ) 1.4 Hz, 1H; H4),

3

7.215 (dd, J(5,4) ) 7.9 Hz, J(5,6) ) 4.7 Hz, 1H; H5), 3.331

(s, 1H; -CtCH), 1.148 ppm (s, 21H; CH(CH₃)₂). ¹³C NMR

(CDCl₃, 100.6 MHz, 25 °C): δ ) 148.6, 144.3, 139.5, 123.6,

J. Org. Chem, Vol. 70, No. 13, 2005 4949

Baxter and Dali-Youcef

122.5, 102.2 (-Ct), 99.0 (-Ct), 81.6 (-Ct), 80.8 (-Ct), 18.6

(CH(CH₃)₂), 11.2 ppm (CH(CH₃)₂). IR (thin film): 3309 (s) (H-

Ct), 3217 (m, broad) (H-Ct), 3041 (w), 2943 (s), 2865 (s),

2160 (m) (CtC), 2109 (m) (CtC), 1549 (m), 1463 (s), 1444 (m),

1414 (s), 1099 (s), 997 (m), 883 (s), 861 (m), 802 (m), 769 (s),

748 (s), 678 (s), 662 (s), 639 cm^-1(s). FABMS: m/z 284 (100)

[M⁺+ H], 240 (8) [M⁺- {CH₂(CH₃)₂}], 212 (3) [M⁺- {CH₂-

(CH₃)₂} - 2{CH₂}], 198 (4) [M⁺- {CH₂(CH₃)₂} - 3{CH₂}].

HRMS (FAB, [M⁺+ H]): calcd for C₁₈H₂₆NSi 284.1835, found

284.1828.

dissolved in boiling hexane (15 mL), gravity filtered, and the

solvent removed under reduced pressure on a water bath at

ambient temperature to afford 30 (0.690 g, 76%) after drying

under vacuum (ambient temperature/0.01 mmHg) as a pungent-

smelling pale yellow oil. ¹H NMR (CDCl₃, 500 MHz, 25 °C): δ

) 8.549 (dd, ³J(6,5) ) 4.7 Hz, ⁴J(6,4) ) 1.5 Hz, 1H; H6), 8.139

(dd, ³J(4,5) ) 8.1 Hz, ⁴J(4,6) ) 1.5 Hz, 1H; H4), 6.996 (dd,

³J(5,4) ) 8.0 Hz, ³J(5,6) ) 4.6 Hz, 1H; H5), 3.417 ppm (s, 1H;

-CtCH). ¹³C NMR (CDCl₃, 125.8 MHz, 25 °C): δ ) 148.9,

146.5, 146.1, 124.2, 98.1 (C-I), 83.8 (-Ct), 80.9 ppm (-Ct).

IR (thin film): 3286 (s) (H-Ct), 3207 (s, broad) (H-Ct), 3039

(m), 2112 (s) (CtC), 1561 (s), 1542 (s), 1429 (s), 1408 (s), 1123

(s), 1061 (s), 1009 (s), 793 (s), 752 (s), 657 (s), 645 cm^-1(s).

FABMS: m/z 230 (100) [M⁺+ H]. HRMS (FAB, [M⁺+ H]):

calcd for C₇H₅IN 229.9467, found 229.9472.

1-[3-(4-Trimethylsilylethynyl)pyridyl]-2-[3-(4-triiso-

propylsilylethynyl)pyridyl]ethyne (31). Using general

procedure A, a mixture of 11 (0.478 g, 1.59 × 10^-3mol), 21

(0.387 g, 1.37 × 10^-3mol), and PdCl₂(PPh₃)₂(0.042 g, 5.98 ×

10^-5mol) in Et₃N (20 mL) and a solution of CuI (0.040 g, 2.10

× 10^-4mol) in Et₃N (2.5 mL) were stirred at ambient

temperature for 5 d. The crude product was chromatographed

(silica/CH₂Cl₂) and then rechromatographed on a fresh silica

column, eluting first with CH₂Cl₂followed by CH₂Cl₂/3%MeOH

and further purified by treatment with NORIT A in pentane

to yield 31 (0.466 g, 75%) as a pale honey-colored oil. ¹H NMR

(CDCl₃, 400 MHz, 25 °C): δ ) 8.782 (s, 1H; 4-triisopropyl-

silylethynylpyridine H2), 8.725 (s, 1H; 4-trimethylsilyleth-

ynylpyridine H2), 8.502 (d, ³J(6,5) ) 5.0 Hz, 2H; 4-triisoprop-

ylsilylethynylpyridine/4-trimethylsilylethynylpyridine H6), 7.378

(d, ³J(5,6) ) 5.3 Hz, 1H; 4-triisopropylsilylethynylpyridine H5),

7.351 (d, ³J(5,6) ) 5.3 Hz, 1H; 4-trimethylsilylethynylpyridine

H5), 1.121 (s, 21H; CH(CH₃)₂), 0.257 ppm (s, 9H; Si(CH₃)₃).

¹³C NMR (CDCl₃, 100.6 MHz, 25 °C): δ ) 152.8, 152.3, 148.52,

148.50, 133.3, 133.1, 125.8, 125.2, 121.5, 121.4, 105.1 (-Ct),

102.3 (-Ct), 102.0 (-Ct), 100.4 (-Ct), 91.9 (-Ct), 91.3

(-Ct), 18.6 (CH(CH₃)₂), 11.2 (CH(CH₃)₂), -0.3 ppm Si(CH₃)₃).

IR (thin film): 3036 (w), 2957 (s), 2943 (s), 2892 (s), 2865 (s),

2162 (m) (CtC), 1574 (s), 1485 (s), 1470 (s), 1407 (s), 1251 (s),

883 (s), 861 (s), 838 (s), 802 (s), 761 (s), 679 (s), 666 cm^-1(s).

FABMS: m/z 457 (100) [M⁺+ H], 413 (12) [M⁺- {CH₂-

(CH₃)₂}]. HRMS (FAB, [M⁺+ H]): calcd for C₂₈H₃₇N₂Si₂

457.2495, found 457.2496.

1,4-Bis(2-(3-triisopropylsilylethynyl)pyridyl)buta-1,3-

diyne (28). Compound 28 (0.296 g, 65%) was obtained as

colorless acicular plates from the reaction between 27 (0.459

g, 1.62 × 10^-3mol) and CuCl (0.019 g, 1.92 × 10^-4mol) in

oxygenated pyridine (30 mL), according to the general coupling

procedure C. During workup, the crude 28 isolated from the

pentane extraction was triturated in MeCN. Mp: 158.0-159.6

1

3

°C. H NMR (CDCl₃, 400 MHz, 25 °C): δ ) 8.521 (dd, J(6,5)

4

3

) 4.8 Hz, J(6,4) ) 1.6 Hz, 2H; H6), 7.769 (dd, J(4,5) ) 7.9

Hz, ⁴J(4,6) ) 1.7 Hz, 2H; H4), 7.223 (dd, ³J(5,4) ) 7.9 Hz,

³J(5,6) ) 5.0 Hz, 2H; H5), 1.146 ppm (s, 42H; CH(CH₃)₂). ¹³C

NMR (CDCl₃, 100.6 MHz, 25 °C): δ ) 148.8, 143.9, 139.4,

124.4, 122.6, 101.8 (-Ct), 100.0 (-Ct), 80.8 (-Ct), 76.8

(-Ct), 18.6 (CH(CH₃)₂), 11.2 ppm (CH(CH₃)₂). IR: 3043 (w),

2960 (s), 2942 (s), 2891 (s), 2864 (s), 2160 (m) (CtC), 2148 (m,

sh) (CtC), 1462 (m), 1403 (s), 1242 (s), 1099 (s), 994 (s), 882

(s), 750 (s), 677 (s), 662 (s), 640 cm^-1(s). FABMS: m/z 565

(100) [M⁺+ H]. HRMS (FAB, [M⁺+ H]): calcd for C₃₆H₄₉N₂-

Si₂565.3434, found 565.3419. Anal. Calcd for C₃₆H₄₈N₂Si₂: C,

76.53; H, 8.56; N, 4.96. Found: C, 76.26; H, 8.63; N, 4.90.

1,4-Bis(2-(3-ethynyl)pyridyl)buta-1,3-diyne (29). A solu-

tion of 28 (0.246 g, 4.35 × 10^-4mol), 2 drops of distilled water,

and a 1.0 M solution of [(n-Bu)₄N]F in THF (1.5 mL, 1.5 ×

10^-3mol) in THF (30 mL) were stirred for 1.5 d and worked

up as described in the general procedure D. The crude product,

which was found to be soluble in MeOH and MeCN, was

dissolved in Et₂O (400 mL), NORIT A (0.08 g) added, the

mixture briefly stirred then gravity filtered, and the solvent

removed under reduced pressure on a water bath at ambient

temperature. The product was further purified by chromatog-

raphy on silica eluting with CH₂Cl₂and then suspended in

Et₂O/pentane (15 mL, 1:1) and filtered under vacuum. The

collected solid was washed with Et₂O/pentane (2 × 2 mL, 1:1)

and air-dried to afford 29 (0.072 g, 65%) as photosensitive

1-[3-(4-Ethynyl)pyridyl]-2-[3-(4-triisopropylsilyleth-

ynyl)pyridyl]ethyne (32). A solution of 31 (0.442 g, 9.68 ×

10^-4mol) in MeOH (27 mL) with K₂CO₃(0.070 g, 5.06 × 10^-4

mol) was stirred for 20 h at ambient temperature. The reaction

was worked up according to the general deprotection procedure

B except that the product was chromatographed by elution on

silica with CH₂Cl₂followed by CH₂Cl₂/3% MeOH. The column

was best shielded from direct light due to the enhanced

photosensitivity of 32. After the chromatographic purification,

the product was directly dried under dynamic vacuum to afford

32 (0.337 g, 91%) as a colorless viscous oil that partly

crystallized upon storage at -30 °C. ¹H NMR (CDCl₃, 400

MHz, 25 °C): δ ) 8.798 (d, ⁵J(2,5) ) 0.6 Hz, 1H; 4-triisoprop-

ylsilylethynylpyridine H2), 8.761 (d, ⁵J(2,5) ) 0.6 Hz, 1H;

1

white fibrous microneedles, pure by H and ¹³C NMR. (Upon

slow heating from below 164.0 °C, the crystals become glossy

black in appearance, with no further visible change up to 310

°C. With rapid heating, 29 ignites explosively at g164.0 °C to

yield a black residue.) ¹H NMR (CDCl₃, 400 MHz, 25 °C): δ )

3

4

8.571 (dd, J(6,5) ) 5.0 Hz, J(6,4) ) 1.4 Hz, 2H; H6), 7.806

(dd, ³J(4,5) ) 7.9 Hz, ⁴J(4,6) ) 1.5 Hz, 2H; H4), 7.268 (dd,

³J(5,4) ) 7.9 Hz, J(5,6) ) 4.7 Hz, 2H; H5) 3.501 ppm (s, 2H;

3

-CtCH). ¹³C NMR (CDCl₃, 100.6 MHz, 25 °C): δ ) 149.5,

144.0, 139.7, 123.3, 122.9, 84.9 (-Ct), 80.4 (-Ct), 79.0 ppm

(-Ct). ¹³C NMR (CD₂Cl₂, 100.6 MHz, 25 °C): δ ) 150.3, 144.2,

140.4, 123.8, 123.7, 85.2 (-Ct), 81.1 (-Ct), 79.6 (-Ct), 76.4

ppm (-Ct). IR: 3210 (s) (H-Ct), 3068 (w), 2106 (m) (CtC),

1412 (s), 1099 (m), 808 (s), 763 cm^-1(s). FABMS: m/z 253 (100)

[M⁺+ H]. HRMS (FAB, [M⁺+ H]): calcd for C₁₈H₉N₂

253.0766, found 253.0772.

3

4-ethynylpyridine H2), 8.538 (d, J(6,5) ) 5.2 Hz, 1H; 4-eth-

ynylpyridine H6), 8.510 (d, ³J(6,5) ) 5.0 Hz, 1H; 4-triiso-

propylsilylethynylpyridine H6), 7.404 (dd, ⁵J(5,2) ) 0.6 Hz,

³J(5,6) ) 5.3 Hz, 1H; 4-ethynylpyridine H5), 7.375 (dd, ⁵J(5,2)

) 0.7 Hz, ³J(5,6) ) 5.1 Hz, 1H; 4-triisopropylsilylethynyl-

pyridine H5), 3.569 (s, 1H; -CtCH), 1.116 ppm (m, 21H; CH-

(CH₃)₂). ¹³C NMR (CDCl₃, 100.6 MHz, 25 °C): δ ) 153.0, 152.4,

148.6, 133.1, 132.3, 125.8, 125.7, 121.8, 121.2, 102.3 (-Ct),

102.0 (-Ct), 92.0 (-Ct), 90.8 (-Ct), 86.2 (-Ct), 79.5

(-Ct), 18.6 (CH(CH₃)₂), 11.1 ppm (CH(CH₃)₂). IR (thin film):

3302 (m) (H-Ct), 3197 (m, broad) (H-Ct), 3037 (w), 2943

(s), 2890 (s), 2865 (s), 2107 (m) (CtC), 1578 (s), 1485 (s), 1463

(s), 1407 (s), 878 (s), 831 (s), 771 (s), 679 (s), 665 (s), 643 cm^-1

2-Ethynyl-3-iodopyridine (30). A THF (40 mL) solution

of 25 (1.187 g, 3.94 × 10^-3mol), distilled water (1.0 mL), and

a 1.0 M solution of [(n-Bu)₄N]F in THF (4.1 mL, 4.1 × 10^-3

mol) were stirred for 20 h as described in the general procedure

D. All solvent was removed from the reaction under reduced

pressure on a water bath at ambient temperature, water (30

mL) added, and the emulsion extracted with Et₂O (3 × 20 mL).

The combined organic extracts were extracted with water (5

× 30 mL), dried (anhydrous Na₂SO₄), and filtered, and the

solvent was removed under reduced pressure on a water bath

at ambient temperature. The product was further purified by

chromatography on silica, eluting with CH₂Cl₂, and then

(s). FABMS: m/z 385 (100) [M⁺+ H]. HRMS (FAB, [M⁺

H]): calcd for C₂₅H₂₉N₂Si 385.2100, found 385.2105.

+

4950 J. Org. Chem., Vol. 70, No. 13, 2005

Nitrogen Heterocyclic Carbon-Rich Materials

1,4-bis[4-(3-{2,1-ethynediyl-3-(4-triisopropylsilylethynyl)-

pyridyl})pyridyl]buta-1,3-diyne (33) (from 32). Compound

33 (0.248 g, 77%) was obtained as cream-colored flakes from

the reaction between 32 (0.322 g, 8.37 × 10^-4mol) and CuCl

(0.010 g, 1.01 × 10^-4mol) in oxygenated pyridine (30 mL),

according to the general coupling procedure C. During workup,

the crude 33 isolated from the pentane extraction was tritu-

H6), 7.457 (d, ³J(5,6) ) 5.2 Hz, 2H; bis[4-pyridyl]butadiyne

H5), 7.322 (d, ³J(5,6) ) 5.0 Hz, 2H; 4-ethynylpyridine H5),

3.694 (s, 2H; -CtCH). ¹³C NMR (CDCl₃, 100.6 MHz, 25 °C):

δ ) 153.0, 152.8, 148.9, 148.8, 132.2, 131.0, 125.8, 125.7, 121.9,

121.4, 92.3 (-Ct), 91.1 (-Ct), 86.6 (-Ct), 81.2 (-Ct), 80.6

(-Ct), 79.4 ppm (-Ct). UV/vis (CH₂Cl₂): λ_maxnm (ꢀ) ) 247

(68678), 284 (36704), 317 (34602), 348 (25819), 374 nm (sh)

(12082 M^-1cm^-1). Fluorescence emission ([34] e 4.4 × 10^-5

M in CH₂Cl₂; 350 nm excitation): λ_max) 391, 414 nm (sh). IR:

3292 (s) (H-Ct), 3204 (s) (H-Ct), 3029 (w), 2214 (w) (CtC),

2116 (w) (CtC), 2104 (m) (CtC), 1579 (s), 1570 (s), 1411 (s),

841 (s), 822 (s), 642 (s), 573 cm^-1(s). FABMS: m/z 455 (100)

[M⁺+ H]. HRMS (FAB, [M⁺+ H]): calcd for C₃₂H₁₅N₄

455.1297, found 455.1290. Anal. Calcd for C₃₂H₁₄N₄: C, 84.57;

H, 3.11; N, 12.33. Found: C, 84.22; H, 2.96; N, 12.27.

1

rated in MeOH. Mp: 140.5-142.0 °C. H NMR (CDCl₃, 400

5

MHz, 25 °C): δ ) 8.835 (d, J(2,5) ) 0.9 Hz, 2H; 4-triisopro-

pylsilylethynylpyridine H2), 8.778 (d, ⁵J(2,5) ) 0.9 Hz, 2H;

bis[4-pyridyl]butadiyne H2), 8.569 (d, ³J(6,5) ) 5.0 Hz, 2H;

bis[4-pyridyl]butadiyne H6), 8.499 (d, ³J(6,5) ) 5.3 Hz, 2H;

4-triisopropylsilylethynylpyridine H6), 7.455 (dd, ⁵J(5,2) ) 0.9

3

Hz, J(5,6) ) 5.3 Hz, 2H; bis[4-pyridyl]butadiyne H5), 7.366

(dd, ⁵J(5,2) ) 0.9 Hz, ³J(5,6) ) 5.2 Hz, 2H; 4-triisopropyl-

silylethynylpyridine H5), 1.118 ppm (m, 42H; CH(CH₃)₂). ¹³C

NMR (CDCl₃, 100.6 MHz, 25 °C): δ ) 153.1, 152.5, 148.7,

148.6, 133.1, 131.3, 125.8, 125.7, 122.1, 121.0, 102.2 (-Ct),

102.1 (-Ct), 93.0 (-Ct), 90.5 (-Ct), 81.0 (-Ct), 80.3 (-Ct),

18.6 (CH(CH₃)₂), 11.1 ppm (CH(CH₃)₂). UV/vis (CH₂Cl₂): λ_max

(ꢀ) ) 244 (sh) (73950), 251 (76457), 301 (32749), 312 (32098),

354 (23406), 375 nm (sh) (11535 M^-1cm^-1). Fluorescence

emission ([33] e 3.0 × 10^-5M in CH₂Cl₂; 353 nm excitation):

λ_max) 393, 414 nm (sh). IR: 2942 (s), 2864 (s), 2164 (vw)

(CtC), 2151 (w) (CtC), 1576 (s), 1484 (s), 1403 (s), 879 (s),

831 (s), 774 (s), 678 (s), 666 (s), 577 cm^-1(m). FABMS: m/z

767 (100) [M⁺+ H], 723 (11) [M⁺- {CH₂(CH₃)₂}]. HRMS

(FAB, [M⁺+ H]): calcd for C₅₀H₅₅N₄Si₂767.3965, found

767.3980. Anal. Calcd for C₅₀H₅₄N₄Si₂: C, 78.28; H, 7.10; N,

7.30. Found: C, 78.10; H, 7.11; N, 7.16.

Dehydrotetrapyrido[20]annulene (1). To a stirred solu-

tion of [Cu₂(OAc)₄]‚2H₂O (2.320 g, 5.81 × 10^-3mol) in pyridine

(600 mL) was added a hot solution of 34 (0.132 g, 2.90 × 10^-4

mol) in pyridine (25 mL) over 3 h. The reaction was stirred

for 21 d, the solvent removed, and the residue treated with

aqueous KCN as described in general procedure F above. The

aqueous suspension was then extracted with warm CHCl₃(200

mL) and the emulsion filtered through a G2 frit under gentle

vacuum. The dried solid collected and the aqueous portion of

the filtrate were each further extracted with CHCl₃(2 × 100

mL). All organic extracts were combined and gravity filtered

and the solvent removed by distillation on a water bath to

afford crude 1, which was chromatographed twice on alumina

(neutral, activity II/III) eluting first with CH₂Cl₂and finally

CH₂Cl₂/1%MeOH. The columns must be shielded from direct

light due to the enhanced photosensitivity of the product. The

solid thus obtained was dissolved in boiling toluene (6 mL)

and gravity filtered, the solvent removed under reduced

pressure on a water bath, and MeCN (2 mL) added. The

suspension was briefly stirred and filtered under vacuum and

the collected solid washed with MeCN (3 × 0.5 mL), air-dried,

and further dried under vacuum (70 °C/0.01 mmHg) to afford

1,4-bis[4-(3-{2,1-ethynediyl-3-(4-triisopropylsilylethynyl)-

pyridyl})pyridyl]buta-1,3-diyne (33) (from 15 + 19). A

mixture of 15 (0.100 g, 3.96 × 10^-4mol) and [PdCl₂(dppf)]‚

CH₂Cl₂(0.016 g, 1.96 × 10^-5mol) in toluene (16 mL, N₂

bubbled) under argon was briefly heated until all the sus-

pended 15 had dissolved. The stirred reaction was then placed

in a bath at 60 °C, and a solution of 19 (0.406 g, 1.05 × 10^-3

mol) and CuI (0.015 g, 7.88 × 10^-5mol) in Et₃N (1.5 mL) were

added consecutively via syringe. The reaction was monitored

by TLC sampling, which indicated that the 15 had been

consumed by 22 h. The solvent was then removed under

reduced pressure on a hot water bath and the residue chro-

matographed first on alumina (neutral, activity II/III) with

CH₂Cl₂and CH₂Cl₂/1% MeOH, followed by elution on alumina

(basic, activity III/IV) with CH₂Cl₂. The product was thus

obtained as a clear glass, which crystallized after addition of

MeOH (4 mL) and brief heating. Filtration of the cooled

mixture under vacuum and washing the collected solid with

MeOH, followed by air-drying and further drying under

dynamic vacuum, afforded 33 (0.146 g, 48%) as colorless

microflakes. Mp: 142.0-142.8 °C. Anal. Calcd for C₅₀H₅₄N₄-

Si₂: C, 78.28; H, 7.10; N, 7.30. Found: C, 78.04; H, 7.13; N,

7.09.

1 (0.053 g, 40%) as colorless microneedles (pure by ¹H and ¹³

C

NMR). (Slow heating from below 267.5 °C up to 310 °C causes

the crystals to become glossy black in appearance. Upon rapid

heating, 1 explosively ignites at g267.5 °C to yield a glossy

1

black residue.) H NMR (CDCl₃, 400 MHz, 25 °C): δ ) 8.834

(s, 4H; H2), 8.570 (d, ³J(6,5) ) 5.0 Hz, 4H; H6), 7.419 ppm (d,

³J(5,6) ) 5.2 Hz, 4H; H5). ¹³C NMR (CDCl₃, 100.6 MHz, 25

°C): δ ) 152.0 (C2), 148.8 (C6), 132.0, 125.8 (C5), 121.5, 91.5

(-Ct), 81.2 (-Ct), 80.1 ppm (-Ct). UV/vis (CH₂Cl₂): λ_max

(ꢀ) ) 256 (119963), 268 (129267), 294 (sh) (34713), 318 (28478),

333 (sh) (24193), 354 nm (sh) (12429 M^-1cm^-1). Fluorescence

emission ([1] e 8.8 × 10^-5M in CH₂Cl₂; 330 nm excitation):

λ_max) 443 nm. IR: 3033 (vw), 2219 (vw) (CtC), 2158 (w)

(CtC), 2142 (w) (CtC), 1570 (s), 1481 (m), 1468 (m), 1416 (m),

826 (s), 801 cm^-1(m). FABMS: m/z 453 (100) [M⁺+ H]. HRMS

(FAB, [M⁺+ H]): calcd for C₃₂H₁₃N₄453.1140, found 453.1140.

1,4-bis[4-(3-{2,1-ethynediyl-3-(4-ethynyl)pyridyl})-

pyridyl]buta-1,3-diyne (34). A solution of 33 (0.258 g, 3.36

× 10^-4mol), 14 drops of distilled water, and a 1.0 M solution

of [(n-Bu)₄N]F in THF (0.9 mL, 9.0 × 10^-4mol) in THF (33

mL) were stirred for 20 h and worked up as described in the

general procedure D. The crude 34 was suspended in MeOH

(20 mL), homogenized by brief stirring, and then filtered under

vacuum, washed with MeOH (5 × 2 mL), Et₂O (3 × 2 mL),

and air-dried to afford 34 (0.150 g, 99%) as an amorphous

white solid, pure by ¹H and ¹³C NMR. The product was

obtained as analytically pure microcrystalline needles upon

recrystallization from boiling toluene, to which NORIT A (0.07

g) had been added prior to gravity filtration. Mp: upon slow

heating, the crystals become glossy black-brown in appearance

between 195 and 225 °C, with no further visible change up to

1-[2-(Trimethylsilylethynylphenyl)]-2-[3-(4-triiso-

propylsilylethynyl)pyridyl]ethyne (36). Using general

procedure A, a mixture of 21 (0.502 g, 1.77 × 10^-3mol), 35

(0.562 g, 1.87 × 10^-3mol), and PdCl₂(PPh₃)₂(0.051 g, 7.27 ×

10^-5mol) in toluene (18 mL) and a solution of CuI (0.052 g,

2.73 × 10^-4mol) in Et₃N (4 mL) were stirred at ambient

temperature for 6 d. The crude 36 thus obtained was chro-

matographed (silica/CH₂Cl₂), redissolved in CH₂Cl₂(30 mL),

and vigorously shaken with a mixture of powdered ascorbic

acid (1 g) and KCN (1 g) followed by gravity filtration in order

to remove the accompanying paramagnetic impurities. The

product was then dissolved in MeCN (40 mL), NORIT A (0.2

g) added, the mixture briefly stirred and gravity filtered, and

the solvent removed under reduced pressure on a water bath

at ambient temperature. Further drying under dynamic

vacuum (0.01 mmHg/12 h) afforded 36 (0.625 g, 77%) as a pale

1

320 °C. H NMR (CDCl₃, 400 MHz, 25 °C): δ ) 8.864 (s, 2H;

1

bis[4-pyridyl]butadiyne H2), 8.840 (s, 2H; 4-ethynylpyridine

H2), 8.593 (d, ³J(6,5) ) 5.3 Hz, 2H; bis[4-pyridyl]butadiyne

H6), 8.499 (d, ³J(6,5) ) 5.0 Hz, 2H; 4-ethynylpyridine

honey-colored viscous oil. H NMR (CDCl₃, 400 MHz, 25 °C):

δ ) 8.789 (s, 1H; pyridine H2), 8.475 (d, ³J(6,5) ) 5.2 Hz, 1H;

3

pyridine H6), 7.507 (m, 2H; phenyl H3/6), 7.374 (d, J(5,6) )

J. Org. Chem, Vol. 70, No. 13, 2005 4951

Baxter and Dali-Youcef

5.0 Hz, 1H; pyridine H5), 7.291 (m, 2H; phenyl H4/5), 1.121

(m, 21H; CH(CH₃)₂), 0.237 ppm (s, 9H; Si(CH₃)₃). ¹³C NMR

(CDCl₃, 100.6 MHz, 25 °C): δ ) 152.5, 147.6, 133.2, 132.2,

131.8, 128.5, 128.0, 126.0, 125.9, 125.3, 122.2, 103.2 (-Ct),

102.5 (-Ct), 101.9 (-Ct), 99.3 (-Ct), 94.9 (-Ct), 88.8

(-Ct), 18.6 (CH(CH₃)₂), 11.2 (CH(CH₃)₂), -0.05 ppm Si(CH₃)₃).

IR (thin film): 3060 (w), 2943 (s), 2892 (s), 2865 (s), 2221 (w)

(CtC), 2160 (s) (CtC), 1574 (s), 1485 (s), 1464 (s), 1443 (s),

1399 (s), 1250 (s), 882 (s), 833 (s), 798 (s), 758 (s), 679 (s), 665

(s), 643 cm^-1(s). FABMS: m/z 456 (100) [M⁺+ H], 412 (18)

[M⁺- {CH₂(CH₃)₂}]. HRMS (FAB, [M⁺+ H]): calcd for C₂₉H₃₈-

NSi₂456.2543, found 456.2547.

NMR. The product was further purified for elemental analysis

by three recrystallizations from toluene as microrectangular

plates. (Upon slow heating, the crystals become glossy black-

brown in appearance between 180 and 215 °C, with no further

1

visible change up to 320 °C.) H NMR (CDCl₃, 400 MHz, 25

5

°C): δ ) 8.834 (d, J(2,5) ) 0.6 Hz, 2H; pyridine H2), 8.446

3

(d, J(6,5) ) 5.3 Hz, 2H; pyridine H6), 7.612 (m, 4H; phenyl

H3/6), 7.379 (m, 4H; phenyl H4/5), 7.285 (dd, ³J(5,6) ) 5.0 Hz,

⁵J(5,2) ) 0.6 Hz, 2H; pyridine H5), 3.760 ppm (s, 2H; -Ct

CH). ¹³C NMR (CDCl₃, 100.6 MHz, 25 °C): δ ) 152.8, 148.2,

133.2, 132.6, 132.0, 129.1, 128.8, 126.0, 125.6, 124.2, 122.2,

94.4 (-Ct), 89.2 (-Ct), 86.6 (-Ct), 81.6 (-Ct), 79.5 (-Ct

), 78.4 ppm (-Ct). UV/vis (CH₂Cl₂): λ_max(ꢀ) ) 240 (73777),

259 (sh) (53736), 286 (40376), 317 (36925), 343 (26925), 368

nm (13932 M^-1cm^-1). Fluorescence emission ([39] e 3.5 × 10^-5

M in CH₂Cl₂; 344 nm excitation): λ_max) 378, 397, 407 nm

(sh). IR: 3180 (s) (H-Ct), 2103 (s) (CtC), 1581 (s), 1486 (s),

1438 (s), 1402 (s), 1377 (s), 832 (s), 771 (s), 752 (s), 722 (s),

578 cm^-1(s). FABMS: m/z 453 (100) [M⁺+ H]. HRMS (FAB,

[M⁺+ H]): calcd for C₃₄H₁₇N₂453.1392, found 453.1387. Anal.

Calcd for C₃₄H₁₆N₂: C, 90.25; H, 3.56; N, 6.19. Found: C, 89.84;

H, 3.77; N, 6.05.

1-[2-(Ethynylphenyl)]-2-[3-(4-triisopropylsilylethynyl)-

pyridyl]ethyne (37). A solution of 36 (0.604 g, 1.33 × 10^-3

mol) in MeOH (35 mL) with K₂CO₃(0.097 g, 7.02 × 10^-4mol)

was stirred for 1.5 d at ambient temperature. The reaction

was worked up as described in the general deprotection

procedure B (with omission of the step involving treatment

with NORIT A in MeOH) to afford 37 (0.447 g, 88%) as a light

honey-colored oil. ¹H NMR (CDCl₃, 400 MHz, 25 °C): δ ) 8.799

3

(s, 1H; pyridine H2), 8.475 (d, J(6,5) ) 5.2 Hz, 1H; pyridine

3

H6), 7.537 (m, 2H; phenyl H3/6), 7.368 (d, J(5,6) ) 5.0 Hz,

1H; pyridine H5), 7.328 (m, 2H; phenyl H4/5), 3.352 (s, 1H;

-CtCH), 1.118 ppm (m, 21H; CH(CH₃)₂). ¹³C NMR (CDCl₃,

100.6 MHz, 25 °C): δ ) 152.7, 147.8, 133.2, 132.6, 131.9, 128.5,

128.4, 125.8, 125.6, 124.9, 122.1, 102.5 (-Ct), 101.8 (-Ct),

94.3 (-Ct), 89.0 (-Ct), 81.9 (-Ct), 81.6 (-Ct), 18.6 (CH-

(CH₃)₂), 11.2 ppm (CH(CH₃)₂). IR (thin film): 3304 (m) (H-

Ct), 3216 (w, broad) (H-Ct), 3060 (w), 2942 (s), 2890 (s), 2864

(s), 2221 (w) (CtC), 2162 (w) (CtC), 2104 (w) (CtC), 1574

(s), 1486 (s), 1463 (s), 1399 (s), 876 (s), 826 (s), 758 (s), 679 (s),

Dehydrodibenzodipyrido[20]annulene (2). To a stirred

solution of anhydrous Cu₂(OAc)₄(2.909 g, 8.01 × 10^-3mol) in

pyridine (500 mL) was added a hot solution of 39 (0.181 g,

4.00 × 10^-4mol) in toluene (100 mL) over 7 h. The reaction

was stirred for 25 d, the solvent removed, and the residue

treated with aqueous KCN as described in general procedure

F above. The aqueous suspension was filtered under vacuum

and the collected solid washed with excess distilled water and

air-dried. The solid was briefly ultrasonicated and boiled in

CH₂Cl₂(50 mL) and the suspension chromatographed on silica,

gradient eluting with CH₂Cl₂/n% MeOH (n ) 1, 3, 5, and 10).

The crude 2 thus obtained was suspended in MeCN (10 mL),

briefly ultrasonicated, isolated by filtration under vacuum,

washed with MeCN (3 × 1 mL), and chromatographed on

alumina (neutral, activity II/III), eluting with CH₂Cl₂. Product

2 was then redissolved in CH₂Cl₂(10 mL) and gravity filtered

and the solvent removed by distillation on a water bath. The

product was finally resuspended in MeCN (10 mL), briefly

ultrasonicated, filtered under vacuum, washed with MeCN (3

× 2 mL), and air-dried to afford 2 (0.142 g, 79%) as a white

microcrystalline solid (pure by ¹H and ¹³C NMR). (Slow heating

from below 264.0 °C up to 310 °C induces the crystals to

become glossy black in appearance. Upon rapid heating, 2

explosively ignites at g264.0 °C to yield a glossy black residue.)

¹H NMR (CDCl₃, 400 MHz, 25 °C): δ ) 8.796 (d, ⁵J(2,5) ) 0.6

Hz, 2H; pyridine H2), 8.511 (d, ³J(6,5) ) 5.3 Hz, 2H; pyridine

665 cm^-1(s). FABMS: m/z 384 (100) [M⁺+ H], 340 (7) [M⁺

-

{CH₂(CH₃)₂}]. HRMS (FAB, [M⁺+ H]): calcd for C₂₆H₃₀NSi

384.2148, found 384.2147.

1,4-bis[2-{2,1-ethynediyl-3-(4-triisopropylsilylethynyl)-

pyridyl}phenyl]buta-1,3-diyne (38). A solution of 37 (0.427

g, 1.11 × 10^-3mol) and CuCl (0.013 g, 1.31 × 10^-4mol) in

oxygenated pyridine (30 mL) was stirred at ambient temper-

ature for 48 h according to the general coupling procedure C.

The crude 38 was isolated from the pentane extraction as an

oil which did not crystallize upon drying under vacuum or

treatment with MeOH and MeCN. The product was therefore

flash chromatographed on silica, gradient eluting successively

with CH₂Cl₂, CH₂Cl₂/1% MeOH, and CH₂Cl₂/3% MeOH. Com-

pound 38 (0.402 g, 94%) was thus isolated as a viscous honey-

colored oil which hardened into a glass after drying under

dynamic vacuum overnight. ¹H NMR (CDCl₃, 400 MHz, 25

°C): δ ) 8.862 (s, 2H; pyridine H2), 8.459 (d, ³J(6,5) ) 5.3 Hz,

2H; pyridine H6), 7.602 (m, 2H; phenyl H6), 7.523 (m, 2H;

phenyl H3), 7.337 (m, 6H; pyridine H5, phenyl H4/5), 1.121

ppm (m, 42H; CH(CH₃)₂). ¹³C NMR (CDCl₃, 100.6 MHz, 25

°C): δ ) 153.0, 147.9, 133.1, 133.0, 132.0, 128.7, 128.6, 126.2,

125.7, 124.6, 121.9, 102.6 (-Ct), 101.6 (-Ct), 94.1 (-Ct),

89.7(-Ct), 81.2 (-Ct), 78.0 (-Ct), 18.6 (CH(CH₃)₂), 11.2 ppm

(CH(CH₃)₂). UV/vis (CH₂Cl₂): λ_max(ꢀ) ) 239 (82687), 253

(82599), 290 (34950), 322 (sh) (33331), 344 (28592), 367 nm

(16393 M^-1cm^-1). Fluorescence emission ([38] e 2.7 × 10^-5

M in CH₂Cl₂; 345 nm excitation): λ_max) 379, 397, 409 nm

(sh). IR: 3058 (w), 2943 (s), 2890 (s), 2864 (s), 2165 (w) (Ct

C), 1571 (s), 1484 (s), 1464 (s), 1445 (s), 1399 (s), 876 (s), 826

(s), 757 (s), 680 (s), 663 cm^-1(s). FABMS: m/z 765 (100) [M⁺

+ H], 721 (12) [M⁺- {CH₂(CH₃)₂}]. HRMS (FAB, [M⁺+ H]):

calcd for C₅₂H₅₇N₂Si₂765.4060, found 765.4047.

3

H6), 7.568 (m, 4H; phenyl H3/6), 7.391 (dd, J(5,6) ) 5.1 Hz,

⁵J(5,2) ) 0.9 Hz, 2H; pyridine H5), 7.355 ppm (m, 4H; phenyl

H4/5). ¹³C NMR (CDCl₃, 100.6 MHz, 25 °C): δ ) 151.9

(pyridine C2), 148.1 (pyridine C6), 133.3 (phenyl C3/6), 132.0,

131.7 (phenyl C3/6), 128.94 (phenyl C4/5), 128.86 (phenyl C4/

5), 125.7 (pyridine C5), 125.6, 125.1, 122.4, 94.9 (-Ct), 88.2

(-Ct), 81.3 (-Ct), 81.0 (-Ct), 80.2 (-Ct), 78.0 ppm (-Ct).

UV/vis (CH₂Cl₂): λ_max(ꢀ) ) 255 (122058), 269 (125936), 298

(32802), 315 (26045), 353 nm (sh) (10162 M^-1cm^-1). Fluores-

cence emission ([2] e 9.8 × 10^-5M in CH₂Cl₂; 318 nm

excitation): λ_max) 456 nm. IR: 3054 (w), 2218 (w) (CtC), 2158

(w) (CtC), 1574 (s), 1483 (s), 1467 (s), 1446 (m), 1411 (m), 1402

(m), 839 (m), 825 (s), 796 (m), 764 (s), 746 (m), 578 cm^-1(m).

FABMS: m/z 451 (100) [M⁺+ H]. HRMS (FAB, [M⁺+ H]):

calcd for C₃₄H₁₅N₂451.1235, found 451.1228.

(2-Iodophenylethynyl)triisopropylsilane (41). A solu-

tion of 40 (4.743 g, 1.41 × 10^-2mol) in Et₂O (160 mL) was

lithiated with 1.6 M n-BuLi in hexanes (11 mL, 1.76 × 10^-2

mol) and the resulting phenyllithium quenched with a solution

of diiodoethane (5.637 g, 2.00 × 10^-2mol) in Et₂O (20 mL) to

give crude 41 as a brown oil, after initial workup according to

procedure E above. However, in this case, the phenyllithium

solution was stirred at -78 °C for 0.7 h, allowed to warm to 0

°C over 0.5 h, and recooled to -78 °C prior to quenching to

1,4-bis[2-{2,1-ethynediyl-3-(4-ethynyl)pyridyl}phenyl]-

buta-1,3-diyne (39). A THF (40 mL) solution of 38 (0.393 g,

5.14 × 10^-4mol), 10 drops of distilled water, and a 1.0 M

solution of [(n-Bu)₄N]F in THF (1.4 mL, 1.4 × 10^-3mol) were

stirred for 24 h and worked up as described in the general

procedure D. The crude product was suspended in MeOH (30

mL), homogenized by brief ultrasonication, filtered under

vacuum, washed with excess MeOH, and air-dried to afford

39 (0.211 g, 91%) as a cream-colored solid, pure by ¹H and ¹³

C

4952 J. Org. Chem., Vol. 70, No. 13, 2005

Nitrogen Heterocyclic Carbon-Rich Materials

ensure complete lithiation. The product was purified by

the mixture filtered under vacuum, washed with excess

distilled water, EtOH, and Et₂O, and dried under vacuum at

ambient temperature to yield 43 (0.867 g, 95%) as an amor-

phous brown-red solid. IR: 2019 (w), 1953 (m), 1922 (s), 1573

(s), 1568 (s), 1453 (s), 1399 (m), 1271 (m), 1078 (m), 1024 (m),

827 (m), 726 cm^-1(m). Caution!: copper acetylides present

explosive hazards and should never be heated while dry.

distillation under vacuum (130-133 °C/0.005 mmHg) to afford

1

41 (4.455 g, 82%) as a pale yellow oil. H NMR (CDCl₃, 400

MHz, 25 °C): δ ) 7.836 (dd, ³J(3,4) ) 7.9 Hz, ⁴J(3,5) ) 0.9

Hz, 1H; H3), 7.492 (dd, ³J(6,5) ) 7.8 Hz, ⁴J(6,4) ) 1.6 Hz, 1H;

H6), 7.280 (td, ³J(5,4/5,6) ) 7.3 Hz, ⁴J(5,3) ) 1.2 Hz, 1H; H5),

6.984 (td, ³J(4,3/4,5) ) 7.7 Hz, ⁴J(4,6) ) 1.8 Hz, 1H; H4), 1.167

ppm (m, 21H; CH(CH₃)₂). ¹³C NMR (CDCl₃, 100.6 MHz, 25

°C): δ ) 138.7, 133.2, 130.2, 129.3, 127.6, 108.0, 100.8, 95.4

(-Ct), 18.7 (CH(CH₃)₂), 11.4 ppm (CH(CH₃)₂). IR (thin film):

3062 (w), 2941 (s), 2890 (s), 2863 (s), 2159 (s) (CtC), 1460 (s),

1429 (m), 1017 (s), 996 (m), 883 (s), 831 (s), 753 (s), 678 (s),

667 (s), 634 cm^-1(m).

Dehydrotripyrido[12]annulene (3). A homogeneous sus-

pension of 43 (0.810 g, 2.78 × 10^-3mol) in pyridine (52 mL)

was refluxed at 145 °C for 18 h, during which time the color

of the suspension changed from orange-brown to black. The

bulk of the solvent was then removed under reduced pressure

on a water bath. Concentrated aq KCN solution (30 mL) was

added to the black residue and the mixture heated to 90 °C

then stirred at ambient temperature for 0.7 h and extracted

with CHCl₃(5 × 60 mL). The combined CHCl₃extracts were

dried (anhydrous Na₂SO₄) and filtered, the solvent was

distilled off under reduced pressure, and MeOH (10 mL) was

added to the residue. The mixture was filtered under vacuum

and the isolated solid twice chromatographed on alumina

(basic, activity IV) eluting with CH₂Cl₂. The product thus

obtained was suspended in acetone (3 mL), filtered under

vacuum, washed with acetone (2 × 1 mL), and air-dried to

afford 3 (0.013 g, 5%) as a pale yellow fibrous solid. Mp: >350

°C (the product changes color to dark brown at g312 °C with

no observable melting). After the CHCl₃extraction above, an

insoluble amorphous black solid (0.226 g; IR: 2191 (m) (Ct

C), 1594 (s), 831 cm^-1(m)) was isolated from the aqueous

suspension upon filtration under vacuum, washing with excess

dist. water, EtOH and air-drying. Characterization data for

3: ¹H NMR (CDCl₃, 400 MHz, 25 °C; [3] ) 3.3 × 10^-2M): δ

) 8.589 (s, 3H; H2), 8.472 (d, ³J(6,5) ) 5.1 Hz, 3H; H6), 7.231

ppm (d, ³J(5,6)) 5.2 Hz, 3H; H5). ¹³C NMR (CDCl₃, 100.6 MHz,

25 °C; [3] ) 3.3 × 10^-2M): δ ) 152.8 (C2), 150.0 (C6), 134.3,

124.9 (C5), 121.5, 94.4 (-Ct), 92.7 ppm (-Ct). UV/vis (CH₂-

Cl₂): λ_max(ꢀ) ) 272 (82387), 279 (84060), 288 (172135), 308

(10148), 319 (12802), 330 (14653), 343 nm (19448 M^-1cm^-1).

Fluorescence emission ([3] e 4.5 × 10^-5M in CH₂Cl₂, 288 nm

excitation): λ_max) 474, 494, 524 nm. IR: 3028 (s), 2227 (m)

(CtC), 2212 (m) (CtC), 1579 (s), 1489 (s), 1396 (s), 1377 (s),

1,4-bis[4-(3-{2,1-ethynediyl-2-(triisopropylsilylethynyl-

phenyl)})pyridyl]buta-1,3-diyne (42). A mixture of 15

(0.156 g, 6.18 × 10^-4mol), 41 (0.594 g, 1.55 × 10^-3mol), and

[PdCl₂(dppf)]‚CH₂Cl₂(0.027 g, 3.31 × 10^-5mol) in toluene (25

mL, N₂bubbled) under argon was briefly heated until all the

suspended 15 dissolved. The stirred reaction was then placed

in a bath at 60 °C and a solution of CuI (0.026 g, 1.37 × 10^-4

mol) in Et₃N (1.5 mL) added via syringe. Stirring and heating

were maintained for 24 h, by which time TLC of the reaction

indicated that all of the 15 had been consumed. All solvent

was then removed under reduced pressure on a hot water bath

and the residue chromatographed first on alumina (neutral,

activity II/III) with CH₂Cl₂, followed by gradient elution on

silica with CH₂Cl₂/1% MeOH and finally CH₂Cl₂/3% MeOH.

The product was further purified by treatment with NORIT

A in pentane and drying under vacuum, as described in the

general procedure A, to afford 42 (0.225 g, 48%) as a clear pale

brown tacky glass. ¹H NMR (CDCl₃, 400 MHz, 25 °C): δ )

5

3

8.776 (d, J(2,5) ) 0.9 Hz, 2H; pyridine H2), 8.529 (d, J(6,5)

) 5.2 Hz, 2H; pyridine H6), 7.543 (m, 2H; phenyl H3), 7.490

3

5

(m, 2H; phenyl H6), 7.399 (dd, J(5,6) ) 5.2 Hz, J(5,2) ) 0.9

Hz, 2H; pyridine H5), 7.230 (m, 4H; phenyl H4/5), 1.124 ppm

(m, 42H; CH(CH₃)₂). ¹³C NMR (CDCl₃, 100.6 MHz, 25 °C): δ

) 152.4, 148.0, 132.8, 132.7, 131.4, 128.7, 128.1, 125.9, 125.6,

124.7, 122.9, 104.9 (-Ct), 96.4 (-Ct), 95.8 (-Ct), 87.8

(-Ct), 81.0 (-Ct), 80.4 (-Ct), 18.7 (CH(CH₃)₂), 11.3 ppm

(CH(CH₃)₂). UV/vis (CH₂Cl₂): λ_max(ꢀ) ) 237 (sh) (81152), 245

(85222), 297 (31819), 312 (28127), 356 nm (20025 M^-1cm^-1).

Fluorescence emission ([42] e 5.2 × 10^-5M in CH₂Cl₂; 355

nm excitation): λ_max) 417 nm. IR (CHCl₃evapd thin film):

3058 (w), 2942 (s), 2890 (s), 2864 (s), 2216 (w) (CtC), 2156

(m) (CtC), 1570 (s), 1485 (s), 1463 (s), 1442 (m), 883 (s), 873

(m), 827 (m), 767 (s), 757 (s), 678 (s), 662 (s), 639 cm^-1(m).

FABMS: m/z 765 (100) [M⁺+ H]. HRMS (FAB, [M⁺+ H]):

calcd for C₅₂H₅₇N₂Si₂765.4060, found 765.4064.

848 (s), 838 (s), 585 cm^-1(s). FABMS: m/z 304 (100) [M⁺

+

H]. HRMS (FAB, [M⁺+ H]): calcd for C₂₁H₁₀N₃304.0875,

found 304.0880.

Acknowledgment. The Institut Charles Sadron is

acknowledged for financial support. Prof. Alexandre

Varnek is also thanked for the molecular modeling

studies, Y. Guilbert for the TGA measurements, and Dr.

Marie-The´re`se Youinou for constructive comments.

3-Iodo-4-Cu(I)pyridylacetylide (43).

A solution of

CuSO₄‚5H₂O (0.79 g, 3.16 × 10^-3mol) in 28% aq ammonia

(5.2 mL) and distilled water (14 mL) was bubbled with argon

for 0.25 h. NH₂OH‚HCl (0.44 g, 6.33 × 10^-3mol) was then

added, causing the reaction to decolorize with effervescence.

With continued argon bubbling and vigorous stirring, a solu-

tion of 16 (0.719 g, 3.14 × 10^-3mol),in EtOH (20 mL) was

added dropwise. The resulting thick orange suspension was

stirred for a further 24 h, distilled water (20 mL) added, and

Supporting Information Available: General experimen-

tal methods and ¹H and ¹³C spectra of 1-3, 12-13, 16, 18,

25-27, 29-32, 36-38, 41, and 42. This material is available

free of charge via the Internet at http://pubs.acs.org.

JO040276F

J. Org. Chem, Vol. 70, No. 13, 2005 4953

Article Doi

Nitrogen heterocyclic carbon-rich materials: Synthesis and spectroscopic properties of dehydropyridoannulene macrocycles

DOI: 10.1021/jo040276f

Source and publish data:

Authors:

Article abstract of DOI:10.1021/jo040276f

Full text of DOI:10.1021/jo040276f

Products guided by the article

R&D Labs maybe for 860021-99-4

Relevant to this article

Hot Product