Dimethyldihydropyrene-dehydrobenzoannulene hybrids: Studies in aromaticity and photoisomerization

Article abstract of DOI:10.1021/jo020462q

The synthesis and study of dehydrobenzoannulene (DBA)-dimethyldihydropyrene (DDP) hybrids as models for the investigation of aromaticity in weakly diatropic systems is reported. Three new monofused DBA-DDP hybrids have been synthesized, and their NMR spectra are discussed with regard to quantifying the aromaticity remaining in multibenzene-fused DBAs. Nucleus-independent chemical shifts, determined at a series of locations for each compound, bond lengths, and ¹H and ¹³C NMR chemical shifts were calculated and used to probe the aromaticity of these hybrids. Systems where more than one annulene/DBA is fused to the DDP core have also been obtained, and their potential use in photoinduced isomerization applications is discussed.

Full text of DOI:10.1021/jo020462q

Dim eth yld ih yd r op yr en e-Deh yd r oben zoa n n u len e Hybr id s:
Stu d ies in Ar om a ticity a n d P h otoisom er iza tion
David B. Kimball and Michael M. Haley*
Department of Chemistry and the Materials Science Institute, University of Oregon,
Eugene, Oregon 97403-1253
Reginald H. Mitchell,* Timothy R. Ward, and Subhajit Bandyopadhyay
Department of Chemistry, University of Victoria, P.O. Box 3065, Victoria, BC, Canada V8W3V6
Richard Vaughan Williams* and J ohn R. Armantrout
Department of Chemistry, University of Idaho, P.O. Box 442343, Moscow, Idaho 83844-2343
haley@oregon.uoregon.edu; regmitch@uvic.ca; williams@neon.chem.uidaho.edu
Received J uly 11, 2002
The synthesis and study of dehydrobenzoannulene (DBA)-dimethyldihydropyrene (DDP) hybrids
as models for the investigation of aromaticity in weakly diatropic systems is reported. Three new
monofused DBA-DDP hybrids have been synthesized, and their NMR spectra are discussed with
regard to quantifying the aromaticity remaining in multibenzene-fused DBAs. Nucleus-independent
1
chemical shifts, determined at a series of locations for each compound, bond lengths, and H and
13C NMR chemical shifts were calculated and used to probe the aromaticity of these hybrids. Systems
where more than one annulene/DBA is fused to the DDP core have also been obtained, and their
potential use in photoinduced isomerization applications is discussed.
In tr od u ction
control can be achieved through logical substituent
placement,3-5 often the electronic nature must be pre-
imposed at the fundamental level. Since some of the most
promising candidates for NLO and photoisomerization
are highly conjugated sp- and sp2-based systems,5 issues
of aromaticity and induced ring current are quite often
a factor.
In the area of materials research, few topics generate
as much interest as finding next-generation electronics
and photonics.1 Two important fields in this broad
spectrum2 include nonlinear optical (NLO) susceptibility
and photoinduced isomerization. The former has applica-
tions such as laser frequency multiplying and converting
electronic signals to photonic information,3 while the
latter is necessary for single-molecule-based memory
devices.4 Key to both NLO susceptibility and photo-
isomerization is the ability to fine-tune the electronic
characteristics of any suitable system. Although some
Aromaticity in large annulenes6 has been studied for
many years, using a variety of macrocycles as model
structures.7 The addition of sp carbon atoms into conju-
(4) Inter alia: (a) Norsten, T. B.; Branda, N. R. J . Am. Chem. Soc.
2001, 123, 1784-1785. (b) Gobbi, L.; Seiler, P.; Diederich, F.; Gramlich,
V. Helv. Chim. Acta 2000, 83, 1711-1723. (c) Feringa, B. L.; Huck, N.
P. M.; Schoevaars, A. M. Adv. Mater. 1996, 8, 681-684. (d) Fissi, A.;
Pieroni, O.; Balestreri, E.; Amato, C. Macromolecules 1996, 29, 4680-
4685. (e) Ehmann, A.; Gompper, R.; Hartmann, H.; Mu¨ller, T. J . J .;
Polborn, K.; Schu¨ltz, R. Angew. Chem., Int. Ed. Engl. 1994, 33, 572-
575. (f) Feringa, B. L.; J ager, W. F.; de Lange, B. Tetrahedron 1993,
49, 8267-8310.
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H.; Nakanishi, H. J . Mater. Chem. 2000, 10, 819-828. (b) Segura, J .
L.; Martin, N. J . Mater. Chem. 2000, 10, 2403-2435. (c) Coe, B. J .
Chem.sEur. J . 1999, 5, 2464-2471. (d) Samoc, M.; Samoc, A.; Luther-
Davies, B. Synth. Met. 2000, 109, 79-83. (e) Cravino, A.; Moggio, I.;
Dell’Erba, C.; Comoretto, D.; Cuniberti, C.; Dellepiane, G.; Giorgetti,
E.; Grando, D.; Sottini, S. Synth. Met. 1999, 102, 943-944. (f) Spreiter,
R.; Bosshard, C.; Kno¨pfle, G.; Gu¨nter, P.; Tykwinski, R. R.; Schreiber
M.; Diederich, F. J . Phys. Chem. B 1998, 102, 29-32.
(1) (a) Conjugated Polymers and Related Materials: The Inter-
connection of Chemical and Electronic Structure; Salaneck, W. R.,
Lundstro¨m, I., Ranby, B., Eds.; Oxford University Press: Oxford, 1993.
(b) Photonic and Optoelectronic Polymers; J enekhe, S. A., Wynne,
K. J ., Eds.; American Chemical Society: Washington, DC, 1995. (c)
Nonlinear Optics of Organic Molecules and Polymers; Nalwa, H. S.,
Miyata, S., Eds.; CRC Press: New York, 1997. (d) Electronic Materi-
als: The Oligomer Approach; Mu¨llen, K., Wegner, G., Eds.; Wiley-
VCH: Weinheim, Germany, 1998.
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371-376. (b) De La Rue, R.; Smith, C. Nature 2000, 408, 653, 655-
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therein.
10.1021/jo020462q CCC: $22.00 © 2002 American Chemical Society
Published on Web 11/19/2002
8798
J . Org. Chem. 2002, 67, 8798-8811

DDP-DBA Hybrids
gated macrocycles, i.e., dehydroannulenes (DAs), can
have surprising consequences. For more complex annu-
lenes such as multiple-arene-fused systems and extended
acetylenic macrocycles, i.e., dehydrobenzoannulenes
(DBAs), traditional theories of aromaticity and ring
currents are insufficient to predict or explain electronic
character. Combining our studies8 with those of Voll-
hardt,9 Youngs,10 Bunz,11 and others,12 we have found the
weak diatropicity in these large systems to be a much
debated and challenging topic of research.
chemists15 and utilized, though not without some dis-
agreement, to predict the aromaticity (or lack thereof)
in DBAs.9,12
In this paper, we present our efforts to assemble
dehydroannulene-fused DDPs and thus determine the
viability of using DDP to probe the aromatic character
of DAs and DBAs.16 1H NMR studies and NICS calcula-
tions of the resultant hybrids (e.g., 1 and 2) should allow
for quantification of the aromaticity of the fused DAs and
DBAs. In addition, it has been shown that the aromaticity
of annulenes fused on opposing faces of a DDP can
facilitate photoinduced isomerization to form the corre-
sponding [2.2]metacyclophanediene.7 We hoped to use
this knowledge to fine-tune the isomerization of the DDP
core between the pyrene and the cyclophanediene forms;
thus, we discuss our work to determine the viability of
using DBA-DDP hybrids (e.g., 3 and 4) for photoswitch-
ing applications.
Two methods based on new experimental and theoreti-
cal models have emerged for the quantification of aro-
maticity. Mitchell has shown that dimethyldihydropyrene
(DDP) can be used as a probe for the bond-fixing ability
of arenes, which can be directly related to the diatropicity
of a specific ring system.7,13 Fusing an aromatic moiety
to the DDP core causes a reduction in the ring current
of the pyrene, which is observable as a change in the
chemical shift of the aromatic protons (δ ≈ 8.5-9 ppm)
and the internal methyl protons (δ ≈ -3.5 to -4.5 ppm).
Any deviation in the DDP ring current will alter the
shielding/deshielding of the DDP protons; thus, compar-
ing these resonance shifts with those induced by a fused
benzene quantifies the aromaticity of the fused arene in
question. To date, however, no DDP systems have been
constructed which incorporate weakly diatropic molecules
such as DBAs because of the difficulty in synthesizing
larger annulene-fused DDP macrocycles.
Schleyer and co-workers developed a computational
method to theoretically corroborate and understand
experimental results regarding ring currents.14 They
defined nucleus-independent chemical shifts (NICS) as
the negative of the absolute shielding calculated using
the Hartree-Fock (HF) gauge-invariant atomic orbital
(GIAO) method, usually at the center of a ring system.
By placing a ghost atom at the center of an aromatic or
antiaromatic ring, one can observe the effects of diatropic
or paratropic ring currents, respectively, manifested in
the absolute shielding of the ghost atom. This powerful
computational technique has been quickly adopted by
(8) (a) Kimball, D. B.; Wan, W. B.; Haley, M. M. Tetrahedron Lett.
1998, 39, 6795-6798. (b) Bell, M. L.; Chiechi, R. C.; J ohnson, C. A.;
Kimball, D. B.; Matzger, A. J .; Wan, W. B.; Weakley, T. J . R.; Haley,
M. M. Tetrahedron 2001, 57, 3507-3520. (c) Wan, W. B.; Chiechi, R.
C.; Weakley, T. J . R.; Haley, M. M. Eur. J . Org. Chem. 2001, 3485-
3490. (d) Boydston, A. J .; Haley, M. M. Org. Lett. 2001, 3, 3599-3601.
(e) Boydston, A. J .; Haley, M. M.; Williams, R. V.; Armantrout, J . R.
J . Org. Chem. 2002, 67, 8812-8819.
Resu lts a n d Discu ssion
Mon ofu sed DDP s a s Ar om a ticity P r obes. The
synthetic strategy for monoannulated DDP hybrids is
based on dibromo-DDP 5 (Scheme 1). Although the
correct regioisomeric dibromide could not be obtained by
direct halogenation of the DDP, this key starting material
was prepared in four steps from monobromo-DDP 6.17
Lithium-halogen exchange followed by addition of
(9) Matzger, A. J .; Vollhardt, K. P. C. Tetrahedron Lett. 1998, 39,
6791-6794.
(10) Zhang, D.; Tessier, C. A.; Youngs, W. J . Chem. Mater. 1999,
11, 3050-3057.
(11) (a) Laskoski, M.; Smith, M. D.; Morton, J . G. M.; Bunz, U. H.
F. J . Org. Chem. 2001, 66, 5174-5181. (b) Laskoski, M.; Steffen, W.;
Smith, M. D.; Bunz, U. H. F. Chem. Commun. 2001, 691-692. (c) Bunz,
U. H. F.; Roidl, G.; Altmann, M.; Enkelmann, V.; Shimizu, K. D. J .
Am. Chem. Soc. 1999, 121, 10719-10726.
(12) (a) J use`lius, J .; Sundholm, D. Phys. Chem. Chem. Phys. 2001,
3, 2433-2437. (b) Alkorta, I.; Rozas, I.; Elguero, J . Tetrahedron 2001,
57, 6043-6049.
(13) (a) Mitchell, R. H.; Iyer, V. S.; Khalifa, N.; Mahadevan, R.;
Venugopalan, S.; Weerawarna, S. A.; Zhou, P. J . Am. Chem. Soc. 1995,
117, 1514-1532. (b) Mitchell, R. H.; Iyer, V. S. J . Am. Chem. Soc. 1996,
118, 2903-2906. (c) Mitchell, R. H.; Chen, Y. Tetrahedron Lett. 1996,
37, 5239-5242.
(14) (a) Schleyer, P. v. R.; Maerker, C.; Dransfeld, A.; J iao, H.; van
Eikema Hommes, N. J . R. J . Am. Chem. Soc. 1996, 118, 6317-6318.
(b) Cyranski, M.; Krygowski, T.; Wisiorowski, M.; Hommes, N.;
Schleyer, P. v. R. Angew. Chem., Int. Ed. 1998, 37, 177-180.
(15) Inter alia: (a) Gomes, J . A. N. F.; Mallion, R. B. Chem. Rev.
2001, 101, 1349-1383. (b) Cyranski, M. K.; Krygowski, T. M.;
Katritzky, A. R.; Schleyer, P. v. R. J . Org. Chem. 2002, 67, 1333-
1338. (c) Schleyer, P. v. R.; Manoharan, M.; Wang, Z.-X.; Kiran, B.;
J iao, H.; Puchta, R.; van Eikema Hommes, N. J . R. Org. Lett. 2001, 3,
2465-2468. (d) Stahl, F.; Moran, D.; Schleyer, P. v. R.; Prall, M.;
Schreiner, P. R. J . Org. Chem. 2002, 67, 1453-1461. (e) West, R.; Buffy,
J . J .; Haaf, M.; Mu¨ller, T.; Gehrhus, B.; Lappert, M. F.; Apeloig, Y. J .
Am. Chem. Soc. 1998, 120, 1639-1640. (f) Chen, Z.; J iao, H.; Hirsch,
A.; Thiel, W. J . Org. Chem. 2001, 66, 3380-3383. (g) Havenith, R. W.
A.; van Lenthe, J . H.; Dijkstra, F.; J enneskens, L. W. J . Phys. Chem.
A 2001, 105, 3838-3845.
(16) Kimball, D. B.; Haley, M. M.; Mitchell, R. H.; Ward, T. R. Org.
Lett. 2001, 3, 1709-1711.
(17) Mitchell, R. H.; Ward, T. R. Tetrahedron 2001, 57, 3689-3695.
J . Org. Chem, Vol. 67, No. 25, 2002 8799

Kimball et al.
fused benzenes.8d,e The resulting hybrid 2 was synthe-
SCHEME 1 a
sized as shown in Scheme 2. Using conditions analogous
to those used for 1, dibromide 5 was cross-coupled to
excess enediyne 1220 to give polyyne 13 in 23% yield.
Desilylation and Cu-mediated cyclization generated hy-
brid 2 in modest yield. Surprisingly, 2 exhibited a smaller
downfield shift of the interior methyl protons (δ -3.91
ppm) compared to that in 11.
SCHEME 2 a
a
Reagents and conditions: (a) 5, PdCl2(PPh3)2, Pd(PPh3)4, CuI,
DMF, Et3N, 100 °C; (b) Bu4NF, MeOH, THF; (c) CuCl, pyridine,
MeOH, THF.
a
Reagents and conditions: (a) BuLi, THF; (b) Me3SiCl; (c) NBS,
Whereas the DDP methyls indicate little or no ring
current of the fused [14]annulene, the alkene protons of
the latter suggest a different story. We8d,e and others11a,b
have shown that the protons on octadehydro[14]annulene
(14), although not as accurate as the DDP skeleton, are
a very good, qualitative indicator of the aromaticity of a
fused-ring system. As shown in Table 1, the alkene
protons in 2 are in approximately the same region as
those in 15, both of which are significantly upfield from
DMF, CH2Cl2; (d) Bu4NF, MeOH, THF; (e) 9, PdCl2(PPh3)2,
Pd(PPh3)4, CuI, DMF, Et3N, 100 °C; (f) CuCl, pyridine, MeOH,
THF.
Me3SiCl gave compound 7, which now has three of the
DDP rings sterically blocked to bromination. Dihaloge-
nation on the remaining open face of 7 with NBS
provided compound 8. Subsequent removal of the silyl
group with fluoride ion gave 5 in 62% yield from 6. Cross-
coupling dibromide 5 with excess 4-tert-butyl-1-ethynyl-
2-(triisopropylsilyl)ethynylbenzene (9), prepared in two
steps from 4-tert-butyl-1-iodo-2-(triisopropylsilyl)ethy-
nylbenzene,18 afforded polyyne 10 in 88% yield. Although
a number of procedures were available, we found that
inclusion of DMF as cosolvent19 was necessary for cross-
couplings with the bromo-DDPs to proceed in very good
yields. Desilylation and cyclization using CuCl in pyri-
dine/THF furnished the desired mono[14]DBA-DDP
hybrid 1 in 26% overall yield from 5.
those in 14. This suggests that the ring current in the
DDP core is about the same as that in a benzene ring.
Interestingly, all three systems show marked downfield
shifts (ca. 0.6-1.8 ppm) of their respective alkene protons
upon cyclization of their polyyne precursors, indicating
the presence of a discernible diatropic ring current.
To examine the effect on the DDP ring current from
the 14-membered cycle, we prepared hybrid 16, where
the bridging alkenes were replaced by alkane units
(Scheme 3). Diyne 1721 was coupled to 5 to give polyyne
1H NMR analysis of 1 showed a small but distinct
downfield shift of the DDP methyl resonances (δ -3.71
ppm) when compared with that of the parent di-tert-
butyl-DDP 11 (δ -4.06 ppm), a result that would be
consistent with an aromatic ring fused to the DDP core.
Nevertheless, the ring currents in DBAs are known to
be very weak; thus, we decided to increase the aroma-
ticity of the dehydro[14]annulene by removal of the two
(18) Wan, W. B.; Haley, M. M. J . Org. Chem. 2001, 66, 3893-3901.
(19) Sjo¨gren, M.; Hansson, S.; Norrby, P.-O.; Akermark, B.; Cucci-
olito, M. E.; Vitagliano, A. Organometallics 1992, 11, 3954-3964.
(20) Lu, Y.-F.; Harwig, C. W.; Fallis, A. G. J . Org. Chem. 1993, 58,
4202-4204.
8800 J . Org. Chem., Vol. 67, No. 25, 2002

DDP-DBA Hybrids
free of strain,23 this would give a better indication of
whether the DDP core could be used to test weakly
diatropic systems.
TABLE 1. Ch em ica l Sh ifts (p p m ) of th e Alk en e P r oton s
in P r ecyclized a n d Cyclized Octa d eh yd r o[14]a n n u len esa
no fusionb
benzo-fusedb
DDP-fused
proton
pre-14
14
pre-15
15
13
2
Ha
Hb
6.05
5.90
7.92
7.39
6.17
5.94
7.41
6.73
6.41
6.00
7.66
6.61
a
b
In CD2Cl2. Reference 8e.
SCHEME 3 a
Unlike previous [18]DBA syntheses, the sluggish re-
activity of 5 necessitated use of sequential acetylene-
haloarene and acetylene-acetylene cross-couplings to
install the initial diyne linkages. Combining 5 with
excess (trimethylsilyl)acetylene afforded diethynyl-DDP
20 in 61% yield (Scheme 4). After desilylation, the
terminal alkynes were subjected to 1-bromoethynyl-
2-(triisopropylsilyl)ethynylbenzene8b using a modified
Cadiot-Chodkiewicz reaction.24 Surprisingly, none of
the expected R,ω-hexayne was obtained; instead, a 7:3
mixture of bis(DDP)-[12]annulene 21 and tris(DDP)-
[18]annulene 22 was obtained in 63% yield. Repetition
SCHEME 4 a
a
Reagents and conditions: (a) 5, PdCl2(PPh3)2, Pd(PPh3)4, CuI,
DMF, Et3N, 100 °C; (b) K2CO3, MeOH, THF; (c) CuCl, pyridine,
MeOH, THF.
18 in 92% yield. Desilylation and Cu-mediated cyclization
gave 16 in low yield. In this case, the chemical shift of
the methyl protons of 16 (δ -3.77 ppm) was essentially
the same as found in 1 (δ -3.71 ppm). These results again
suggest little or no diatropicity for the octadehydro[14]-
annulene nucleus.
For all monofused hybrids studied, the one that shows
the least weakening of the DDP ring current is hybrid 2,
which is exactly the reverse of what we expected. These
curious findings might be attributable to either the
anisotropy of the triple bonds or geometric deformation.
X-ray crystal analysis of related tribenzooctadehydro-
[14]annulene shows significant bending of the triple
bonds.22 This could result in σ inductive effects due to
strain or pronounced π donation from the bent acetylenes.
To test whether this was a factor in our systems, we
attempted the synthesis of mono[18]DBA-DDP 19. Since
[18]DBAs have been shown to be essentially planar and
a
Reagents and conditions: (a) Me3SiCtCH, PdCl2(PPh3)2,
(21) Hillard, R. L., III; Vollhardt, K. P. C. J . Am. Chem. Soc. 1977,
99, 4058-4069.
(22) Baldwin, K. P.; Matzger, A. J .; Scheiman, D. A.; Tessier, C. A.;
Vollhardt, K. P. C.; Youngs, W. J . Synlett 1995, 1215-1218.
Pd(PPh3)4, CuI, DMF, Et3N, 100 °C; (b) Bu4NF, THF, MeOH; (c)
1-(bromoethynyl)-2-(triisopropylsilyl)ethynylbenzene, Pd(dba)2, CuI,
LiI, DMSO, 1,2,2,6,6-pentamethylpiperidine.
J . Org. Chem, Vol. 67, No. 25, 2002 8801

Kimball et al.
TABLE 2. Ch em ica l Sh ifts (p p m ) of Selected Ar en e P r oton s in P r ecyclized a n d Cyclized DBA-DDP Hybr id sa
protonb
10
1
13
2
18
16
20
21
22
H9/14
H11/12
8.46
8.38
8.59
8.48
8.46
8.39
8.69
8.59
8.46
8.38
8.46
8.38
8.47
8.39
8.33
8.27
8.57
8.48
a
b
In CDCl3. Proton numbering corresponds to the DDP assignments in Figure 2 and Table S3.
of this experiment with other conditions for acetylene-
bromoacetylene heterocoupling afforded the same prod-
ucts in slightly different ratios. It is interesting to note,
however, that tris(DDP)-[18]annulene 22 showed a down-
field shift in methyl proton resonances compared to
diethynyl-DDP 20 (δ(Me) -3.56 for 22 and -3.76 for 20).
In addition to the methyl resonances, the DDP arene
protons can be used to estimate the aromaticity of a fused
ring system. The chemical shift values of H9/14 and H11/
12 for the five hybrids and their uncyclized precursors
are given in Table 2. This should be a more valid
comparison for our systems since each of the molecules
contains the same 4,5-diethynyl-DDP moiety, yet the
arene protons in question are sufficiently remote that
effects from conformational bias and anisotropy of the
triple bonds should be negligible. Interestingly, the chem-
ical shifts of the two resonances are within 0.01 ppm for
all four precursors, and are the same as the values for
H9/14 and H11/12 found in 16 (8.46 and 8.38, respec-
tively). Introduction of a ring current in the annelated
cycle shifts the resonances approximately 0.10 ppm
downfield for 1 and 22, and ca. 0.21 ppm downfield for
2. Although a larger difference would be expected for the
stronger diatropicity in 2, the direction of the shift is in
the wrong direction. Surprisingly, all of the NMR data
suggest that the DDP core becomes more aromatic as the
anticipated diatropicity of the fused 14-membered ring
is increased, which is exactly opposite of what is expected.
Com p u ta tion a l Stu d ies. In an effort to explain these
puzzling experimental data, we undertook a theoretical
study of some octadehydro[14]annulenes (ODAs) and
their analogues. The geometries for all compounds in this
study were optimized using the B3LYP/6-31G* method
as implemented in J aguar 4.025 and, for compound 1 only,
the Gaussian 98 suite of programs.26 All optimized
structures were confirmed to be minima through their
calculated energy second derivatives. Gaussian 9826 was
used to calculate NICS values with the GIAO-HF method
on the B3LYP/6-31G*-optimized geometry (GIAO-HF/6-
31G*//B3LYP/6-31G*).
F IGURE 1. Numbering scheme and location of the NICS
points for the DDP nucleus. NICS points are shown in bold
type. Point 30 is 0.2 Å from C17 extended on a line joining
C17 and C18. Point 40 is 0.2 Å from C17 on a line extending
the C15-C17 bond.
+28.8 for cyclobutadiene) and nonaromatics have values
near zero (e.g., -2.1 for cyclohexane).14a NICS values are
basis set dependent. Those reported above for benzene,
cyclobutadiene, and cyclohexane and for the NICS studies
reported herein were calculated using GIAO-HF/6-31G*//
B3LYP/6-31G*.14a NICS have been used to assess the
aromaticities of individual rings in polycyclic aromatics
and are also frequently calculated at points out of the
ring plane(s) to avoid local anisotropies of the
σ
bonds.14,15c,27 Recently, we established that the B3LYP/
6-31G*-calculated structures for three DDPs were in
excellent agreement with the experimental X-ray struc-
tures.28 Furthermore, confirming that the B3LYP/6-31G*
method is appropriate for the investigation of DDPs, we
1
found that H (GIAO-HF/6-31G*//B3LYP/6-31G*) and 13C
(scaled29 from GIAO-B3LYP/6-31G*//B3LYP/6-31G*) NMR
chemical shifts calculated at the optimized B3LYP/6-
31G* geometries for 12 DDPs closely matched the cor-
responding experimental data.28 Using these methods,
we verified that NICS not only allow for a qualitative
detection of aromaticity, but also provide exact correla-
tion with an experimental scale of aromaticity derived
for a large series of DDPs.28 The simple arithmetic
average of NICS (NICSAv) calculated at the centers of the
four six-membered rings (points 1-4, Figure 1) of the
DDP nuclei gave the most reliable ordering of aroma-
ticities of the DDP nucleus.28 In addition, NICS values
determined at the out-of-plane points 30 and 40 (Figure
1) also effectively ordered the aromaticities in the major-
ity of cases studied.28
Schleyer et al. demonstrated that aromatic systems
have negative NICS values (e.g., -11.5 for benzene) while
antiaromatic systems have positive NICS values (e.g.,
We defined the relative aromaticity (RA) of the DDP
nucleus in terms of the nonaromatic model 23 and the
DDP (n ) under investigation referenced to the fully
aromatic parent DDP (24) by means of eqs 1-3.28
(23) Pak, J . J .; Weakley, T. J . R.; Haley, M. M. J . Am. Chem. Soc.
1999, 121, 8182-8192.
(24) Cai, C.; Vasella, A. Helv. Chim. Acta 1995, 78, 2053-2064.
(25) J aguar 4.0, Schro¨dinger, Inc., Portland, OR, 1991-2000.
(26) Gaussian 98, Revision A.9, Frisch, M. J .; Trucks, G. W.;
Schlegel, H. B.; Scuseria, G. E.; Robb, M. A.; Cheeseman, J . R.;
Zakrzewski, V. G.; Montgomery, J . A., J r.; Stratmann, R. E.; Burant,
J . C.; Dapprich, S.; Millam, J . M.; Daniels, A. D.; Kudin, K. N.; Strain,
M. C.; Farkas, O.; Tomasi, J .; Barone, V.; Cossi, M.; Cammi, R.;
Mennucci, B.; Pomelli, C.; Adamo, C.; Clifford, S.; Ochterski, J .;
Petersson, G. A.; Ayala, P. Y.; Cui, Q.; Morokuma, K.; Malick, D. K.;
Rabuck, A. D.; Raghavachari, K.; Foresman, J . B.; Cioslowski, J .; Ortiz,
J . V.; Baboul, A. G.; Stefanov, B. B.; Liu, G.; Liashenko, A.; Piskorz,
P.; Komaromi, I.; Gomperts, R.; Martin, R. L.; Fox, D. J .; Keith, T.;
Al-Laham, M. A.; Peng, C. Y.; Nanayakkara, A.; Challacombe, M.; Gill,
P. M. W.; J ohnson, B.; Chen, W.; Wong, M. W.; Andres, J . L.; Gonzalez,
C.; Head-Gordon, M.; Replogle, E. S. and Pople, J . A., Gaussian, Inc.,
Pittsburgh, PA, 1998.
Similarly, the RA of the ODA nucleus can be defined
using the nonaromatic model 2530 and the appropriate
(27) Patchkovskii, S.; Thiel, W. J . Mol. Model 2000, 6, 67-75.
8802 J . Org. Chem., Vol. 67, No. 25, 2002

DDP-DBA Hybrids
TABLE 3. NICS Va lu es for Com p ou n d s 1, 2, 11, 14, 23, 24, 25, a n d 26
point
1
2
11
14
23
24
25
26
1
2
3
-14.73
-15.22
-13.52
-14.73
-14.55
-34.60
-35.12
0.71
-12.81
-12.98
-11.75
-12.81
-12.59
-34.00
-34.42
-3.87
-18.91
-17.66
-17.66
-18.91
-18.29
-36.18
-36.75
-0.24
-0.09
-0.09
-0.24
-0.07
-27.02
-27.12
-19.15
-18.15
-18.15
-19.15
-18.65
-36.28
-36.84
-15.13
-15.45
-13.78
-15.13
-14.87
-34.84
-35.34
0.67
4
ava
30
40
5
-8.12
0.88
a
Average value of points 1-4.
TABLE 4. Rela tive Ar om a ticities (%) of th e DDP
Nu cleu s of 1, 2, 11, a n d 26
TABLE 5. Rela tive Ar om a ticity (%) of th e ODA Nu cleu s
of 1, 2, a n d 26
a
b
c
a
RAexptl
RAcalcd
RANICS
RANICS 30
RANICS 40
RAexptl(H21) RAcalcd(H21) RAexptl(H22) RAcalcd(H22) RANICS 5
1
2
11
26
89.7
93.5
98.1
78.6
70.1
96.0
80.2
78.1
67.6
98.1
79.8
81.9
75.4
98.9
84.4
82.3
75.1
99.1
84.6
1
2
26
1.9
52.78
2.33
85.1
98.1
51.3
68.0
a
Relative aromaticity (%) calculated using NICS point 5.
a
Relative aromaticity (%) calculated using NICSAv minus the
b
average of NICS points 1-4. Relative aromaticity (%) calculated
using NICS point 30. c Relative aromaticity (%) calculated using
NICS point 40.
δ
calcd(24) ) calculated 1H chemical shift of the Me
groups on 24 (-6.30 ppm),
RANICS ) NICS relative aromaticity of DDP n (com-
pared to 24),
NICS(23) ) NICSAv or NICS value at point 30 or 40
for 23 (0.07, -27.02, and -27.12, respectively),
NICS(n ) ) NICSAv or NICS value at point 30 or 40 for
n , and
ODA (n ) referenced to the fully aromatic parent (14) by
means of eqs 4-6. We optimized the structures (Sup-
porting Information Tables S1 and S2) of 1, 2, 14, 25,
and 26 and used these geometries to calculate their NMR
chemical shifts (1H, Supporting Information Table S3;
13C, Supporting Information Table S4) and NICS values
(Table 3) at the points shown (Figures 1 and 2). The RAs
(Tables 4 and 5) were calculated from these data using
eqs 1-6.
NICS(24) ) NICSAv or NICS value at point 30 or 40
for 24 (-18.65, -36.28, and -36.84, respectively).
ODA nucleus:
DDP nucleus:
δ(25) - δ(n )
δ(25) - δ(14)
RAexptl
)
× 100
(4)
(5)
(6)
δ(23) - δ(n )
δ(23) - δ(24)
RAexptl
)
× 100
(1)
(2)
(3)
δ
calcd(25) - δcalcd(n )
RAcalcd
)
× 100
× 100
δ
calcd(23) - δcalcd(n )
δ
calcd(25) - δcalcd(14)
RAcalcd
)
× 100
× 100
δ
calcd(23) - δcalcd(24)
NICS(25) - NICS(n )
NICS(25) - NICS(14)
RANICS
)
NICS(23) - NICS(n )
NICS(23) - NICS(24)
RANICS
)
RAexptl ) experimental relative aromaticity of ODA n
(compared to 14),
RAexptl ) experimental relative aromaticity of DDP n
(compared to 24),
1
δ(25) ) experimental H chemical shift of H21 or H22
δ(23) ) experimental 1H chemical shift of the Me
groups on 23 (0.97 ppm),
on 25 (6.0 and 5.6 ppm, respectively),
1
δ(n ) ) experimental H chemical shift of H21 or H22
δ(n ) ) experimental 1H chemical shift of the Me groups
(average if different) on annelated DDP,
δ(24) ) experimental 1H chemical shift of the Me
groups on 24 (-4.25 ppm),
on ODA n ,
1
δ(14) ) experimental H chemical shift of H21 or H22
on 14 (7.92 and 7.39 ppm, respectively),
RAcalcd ) calculated relative aromaticity of ODA n
RAcalcd ) calculated relative aromaticity of DDP n
(compared to 24),
(compared to 14),
1
δ
calcd(25) ) calculated H chemical shift of H21 or H22
δ
calcd(23) ) calculated 1H chemical shift of the Me
on 25 (6.17 and 5.79 ppm, respectively),
groups on 23 (1.09 ppm),
1
δ
calcd(n ) ) calculated H chemical shift of H21 or H22
on ODA n ,
calcd(14) ) calculated H chemical shift of H21 or H22
δ
calcd(n ) ) calculated 1H chemical shift of the Me groups
(average if different) on annelated DDP,
1
δ
on 14 (8.32 and 7.79 ppm, respectively),
RANICS ) NICS relative aromaticity of ODA n (com-
pared to 14),
NICS(25) ) NICS value at point 5 for 25 (0.88),
NICS(n ) ) NICS value at point 5 for n , and
NICS(14) ) NICS value at point 5 for 14 (-8.12).
(28) Williams, R. V.; Armantrout, J . R.; Twamley, B.; Mitchell, R.
H.; Ward, T. R.; Bandyopadhyay, S. J . Am. Chem. Soc. 2002, 124,
13495-13505.
(29) Forsyth, D. A.; Sebag, A. B. J . Am. Chem. Soc. 1997, 119, 9483-
9494.
(30) Elbaum, D.; Nguyen, T. B.; J orgensen, W. L.; Schreiber, S. L.
Tetrahedron 1994, 50, 1503-1518.
J . Org. Chem, Vol. 67, No. 25, 2002 8803

Kimball et al.
suggest a greater reduction in diatropicity upon annela-
tion for both nuclei than do the experimental RAs.
All three ODA-DDP hybrids exhibit essentially planar
ODA and DDP nuclei, with their fusion resulting in a
mutual tilting of these planes to give propeller-shaped
molecules of C2 symmetry. The calculated bond lengths
reported in Tables S1 and S2 again indicate reduction
in the diatropicity of both nuclei upon fusion of a DDP
and an ODA. We introduced the alternance parameter
(∆Σ ) average bond length of “a”-type bonds - average
bond length of “b”-type bonds; see Figure 2 for identifica-
tion of a- and b-type bonds) as a measure of the bond
localization/reduction in the diatropicity of the DDP
nucleus upon annelation.28 The greater the magnitude
of ∆Σ, the more localized the DDP and hence the less
diatropic. ∆Σ for 1, 2, and 26 (0.020, 0.031, and 0.019,
respectively) shows a degree of bond localization in the
DDP nucleus of each of these hybrids entirely consistent
with the reduced diatropicities indicated by experiment,
NICS, and RAs. It is interesting to note that the varia-
tions in bond lengths in the ODA nuclei also show some
localization upon annelation. The “single” bonds (4-19,
20-21, 22-23, 24-25, 26-27, 28-29, and 30-5) in 1, 2,
and 26 each show a lengthening compared with those in
14, while the “double” (21-22 and 27-28 in 2) and
“triple” (19-20, 23-24, 25-26, and 29-30) bonds exhibit
a similar shortening in 1, 2, and 26 compared with those
in 14. This adjustment in bond lengths, as expected, is
more apparent in 1 and 26 than in 2.
It is illuminating to compare the results from the above
applications of the various measures of aromaticity to
those for the ODA-DDP hybrids and those previously
reported for di-t-Bu-benzo[e]DDP (27).28 The RAs of 27
F IGURE 2. Numbering scheme and location of the NICS
points for 1, 2, 14, 25, and 26. NICS points are shown in bold
type.
Comparison of the NICS (at point 5, Table 3) for the
parent ODA (14) and the dihydro derivative 25, in which
cyclic delocalization is interrupted, clearly demonstrates
that 14 should indeed be considered as aromatic. Simi-
larly, this comparison also reveals that local anisotropies
associated with the acetylenic bonds are minimal at point
5. We would thus expect fusion of an ODA to a DDP to
result in a reduction in diatropicity of both systems, with
the more diatropic DDP dominating the ODA, causing a
greater attenuation in diatropicity of the ODA than the
DDP. NICSAv and NICS (point 5) for the hybrid 2
immediately confirm this hypothesis, with NICSAv de-
creasing in magnitude from -18.29 in the di-t-Bu-DDP
11 to -12.59 in 2 and NICS (point 5) correspondingly
decreasing from -8.12 to -3.87 in 14 and 2, respectively.
Again, as would be expected, fusion of two benzene rings
to the ODA nucleus in 1 and 26 essentially kills the
aromaticity of the ODA (NICS point 5, 0.71 and 0.67,
respectively) and restores much of the aromaticity of the
DDP nucleus (NICSAv, -14.55 and -14.87, respectively).
We previously found that RAs furnish a reliable ordering
of aromaticity, but that their absolute magnitude is not
of particular significance.28 Examination of the RAexptl
values in Tables 4 and 5 shows that the (experimental)
diatropicity of the di-t-Bu-DDP and ODA nuclei are
decreased upon fusion to form the corresponding hybrid.
Similarly, all calculated RAs support this conclusion and,
in general, in agreement with our earlier findings,28
range from 48.9% (RAexptl) to 25.2% (RANICS(Av)), and the
alternance parameter, ∆Σ, is -0.056. Obviously, benzene
is appreciably more aromatic than ODA 14 and, upon
annelation to the di-t-Bu-DDP, is much more effective
in bond localizing and reducing the diatropicity of the
DDP nucleus.
1
Perusal of the H and 13C chemical shifts presented in
Tables S3 and S4 confirms that the B3LYP/6-31G*
method provides good modeling of the DDPs/ODAs. The
calculated shieldings are for a single conformer of each
compound; we consequently averaged the predicted chemi-
cal shifts (obtained using eqs 7 and 829) for the symmetry-
δcalcd ) σTMS - σ
(7)
(8)
13
δ
( C) ) -1.084σ + 203.1
calcd
related 1H and 13C atoms made equivalent by rotation
of the Me and/or t-Bu groups. The agreement between
8804 J . Org. Chem., Vol. 67, No. 25, 2002

DDP-DBA Hybrids
1
experimental and calculated H chemical shifts is excel-
lent. Experimental 13C chemical shifts are only available
for 1, 14, and 25, where agreement between experiment
and theory is very good. However, the calculated 13C
shifts for the acetylenic carbons in 14 show a significant
deviation from experiment (by as much as 8.33 ppm). The
assignments of experimental chemical shifts are, in the
main, based on the best fit with the calculated data.
A consistent picture emerges from both theory and
experiment. The ODA nucleus is weakly aromatic and
causes bond localization with concomitant reduction in
the diatropicity of the fused DDP; however, one puzzling
aspect of this study persists. Experimentally the 1H NMR
chemical shift of the internal methyl groups of 1 is at
lower field than that of 2, suggesting that the degree of
bond localization/reduction in the diatropicity of the DDP
nucleus is greater in 1 than in 2. Such a suggestion is
clearly contrary to expectations and our calculated results
in which all indicators of aromaticity (including the
calculated 1H chemical shifts for the internal methyls)
firmly place the DDP nucleus of 1 as more aromatic than
that of 2. In most cases where the dihydropyrene nucleus
has been used to probe aromaticity, the change in ring
current caused by the fused system has been fairly large,
and hence, the change in chemical shift observed for the
methyl protons is also large, about 0.5 ppm for each 10%
change in the ring current of the parent 24.7 Generally,
the anisotropy effects of substituents have been small,31
<0.3 ppm, and thus have been ignored. However, as the
aromaticity of the fused system becomes small, this
becomes more risky, and probably has little meaning at
ring currents <10% of that of the parent, because then
anisotropy effects may be playing a role. In our paper on
bond fixation effects caused by fused oxabicyclic rings on
the dihydropyrene system,32 several examples are given
where the anisotropy effects are small, <0.3 ppm, such
that the 0.8 ppm shift observed for 28 was deemed
significant. Likewise the 0.8 ppm shift of the internal
methyl protons of 29 from an acyclic model were deemed
F IGURE 3. Switching between the DDP and CPD forms.
P h otoch em ica l P r op er ties. The fused annulenes
prepared above did not modify the ring currents in the
DDP rings significantly, at least as estimated by the
internal methyl chemical shifts, despite the calculated
aromaticity of the DBA parts. We wondered whether the
photochemical properties of the DDP nucleus would thus
be modified. The DDP nucleus behaves as a photochemi-
cal switch. The properties of this switch are dramatically
changed by fusion of arenes along the faces of the
DDP.13,34 Fusion of a single benzene ring as in 27
facilitates rapid isomerization between the closed (DDP)
form and the open cyclophanediene (CPD) form (Figure
3). When benzene rings are fused on opposite faces, the
cyclophane dominates and the pyrene can only be seen
for a short time at low temperature. The pyrene core
itself, however, is much more stable than its cyclophane
analogue, and the cyclophane can only be achieved with
difficulty. Fused DBA-DDP hybrids are thus of obvious
interest, since the photochemical properties might be
between the two extremes.
With the above in mind, bisfused DBA-DDP hybrids
were synthesized to help fine-tune the isomerization of
the pyrene to the cyclophane. Our initial efforts were
directed toward hybrids 3 and 32.16 Both systems were
synthesized from a common starting compound, tetra-
bromide 30,35 obtained by tetrahalogenation of DDP 11
(Scheme 5). For hybrid 3, excess 1-ethynyl-2-(triisopropyl-
silyl)ethynylbenzene8b was reacted with 30 using Pd-
mediated conditions to provide R,ω-polyyne 31. Desilyl-
ation using Bu4NF and cyclization with CuCl in pyridine
gave 3 in 8% overall yield.
As with the attempted synthesis of 19, hybrid 32
was assembled through sequential acetylene-haloarene
and acetylene-acetylene cross-couplings. Reaction of
30 with excess (dimethylthexylsilyl)acetylene afforded
tetrayne 33 in 33% yield (Scheme 6). After removal of
the silyl protecting groups with Bu4NF, the tetrayne was
coupled to 4 equiv of 1-bromoethynyl-2-(triisopropylsilyl)-
ethynylbenzene8b to give polyyne 34. Desilylation and
cyclization in a Cu(OAc)2/pyridine mixture furnished 32
in 12% overall yield.
1H NMR spectra revealed a downfield shift of the
interior methyl protons in comparison with their precy-
clized, desilylated synthons. The aromaticity of the two
fused [14]- and [18]annulenes, however, could not be
directly related to this shift because of competitive
resonance. For hybrids 3 and 32, the two annulenes are
fused in such a way that for one annulene to bond fix
the DDP would result in the other annulene being bond
significant.33 In the current paper, the difference in the
1H NMR chemical shifts of the internal methyl protons
of 1 (δ -3.71) and 2 (δ -3.91) is only 0.2 ppm, and also
the differences between 1 and 2 and their respective
acyclic precursors 10 (0.06 ppm) and 13 (0.23 ppm) all
fall below the 0.3 ppm advisory limit, and so should not
be used to resolve such finely balanced differences in
aromaticity that are found here.
(31) Mitchell, R. H. In Advances in Theoretically Interesting Mol-
ecules; Thummel, R. P., Ed.; J AI Press Inc.: Stamford, CT, 1989; Vol.
1, pp 135-199.
(32) Mitchell, R. H.; Chen, Y.; Iyer, V. S.; Lau, D. Y. K.; Baldridge,
K. K.; Siegel, J . S. J . Am. Chem. Soc. 1996, 118, 2907-2911.
(33) Mitchell, R. H.; Zhou, P. Tetrahedron Lett. 1991, 44, 6319-
6322.
(34) (a) Mitchell, R. H.; Ward, T. R.; Wang, Y.; Dibble, P. W. J . Am.
Chem. Soc. 1999, 121, 2601-2602. (b) Mitchell, R. H. Eur. J . Org.
Chem. 1999, 2695-2703.
(35) Tashiro, M.; Yamato, T. J . Am. Chem. Soc. 1982, 104, 3701-
3707.
J . Org. Chem, Vol. 67, No. 25, 2002 8805

Kimball et al.
SCHEME 5 a
SCHEME 6 a
a
Reagents and conditions: (a) Br2, CCl4; (b) 1-ethynyl-2-
(triisopropylsilyl)ethynylbenzene, PdCl2(PPh3)2, Pd(PPh3)4, CuI,
DMF, Et3N, 100 °C; (c) Bu4NF, THF, MeOH; (d) CuCl, THF,
pyridine.
fixed as well. This can be confirmed by comparing the
interior methyl shifts of our systems (δ(Me) -3.33 ppm
for 3 and -3.49 ppm for 32) with that of the analogous
bis(benzene-fused) DDP (δ(Me) -3.41 ppm).13c Further
comparison of 3 with a similar structure, tetra(phenyl-
ethynyl)-DDP 35, obtained from the coupling of desilyl-
ated 33 with excess iodobenzene (Scheme 7), shows
virtually identical shifts for their interior methyl protons
(δ(Me) -3.32 ppm for 35).
UV-vis analysis of the two bisfused hybrids revealed
an absorption in the long-wavelength region (Figure 4).
Since previous photoisomerization results using the DDP
core showed isomerization using light at ∼360 nm (for
the CPD) and ∼450 nm (for the DDP), this would allow
for the system to be “read” at a third wavelength that
should not cause unwanted scrambling of information.
Photoisomerization studies, however, were unsuccessful
in that the CPD could not be obtained efficiently because
of extremely facile reversion to the pyrene form.
a
Reagents and conditions: (a) Me2ThSiCtCH, PdCl2(PPh3)2,
Pd(PPh3)4, CuI, DMF, Et3N, 100 °C; (b) Bu4NF, THF, MeOH; (c)
1-(bromoethynyl)-2-(triisopropylsilyl)ethynylbenzene, Pd(dba)2, CuI,
LiI, DMSO, 1,2,2,6,6-pentamethylpiperidine; (d) Cu(OAc)2, THF,
pyridine. Th ) thexyl ) 1,1,2-trimethylpropyl.
SCHEME 7 a
Substituting a benzene ring for one annulene should
slow the ring-closing electrocyclization reaction. The
resultant molecule, DBA-DDP hybrid 4, was constructed
analogously to 1. NBS bromination of benzo-DDP 2717
furnished light-sensitive dibromide 36 in 48% yield
(Scheme 8). Sonogashira coupling of 36 with excess
1-ethynyl-2-(triisopropylsilyl)ethynylbenzene8b in Et3N
and DMF provided polyyne 37 in 77% yield. Desilylation
and cyclization using CuCl in pyridine gave hybrid 4 as
a dark purple solid in 33% overall yield.
a
Reagents and conditions: (a) Bu4NF, THF, MeOH; (b) PhI,
PdCl2(PPh3)2, Pd(PPh3)4, CuI, Et3N.
formation). Both isomers were stable under ambient
conditions. Photoswitching could be achieved within a few
minutes in an NMR tube. The UV-vis spectra of 4 and
its CPD analogue 38 are shown in Figure 5, which depicts
a significant decrease in the absorption at 450 nm and
increase in the absorption at 320 nm in going from the
DDP to the CPD form. Unfortunately, neither state
absorbs appreciably in the 600-800 nm range, where
these systems are intended to be read.
1
As before, H NMR analysis revealed an upfield shift
of the internal methyl protons relative to those of the
uncyclized polyyne (δ(Me) -1.24 for 37 and -1.32 for 4).
Photoisomeriztion, however, could be effected using light
from an overhead projector (to induce cyclophane forma-
tion) and light from a UV lamp (to induce pyrene
8806 J . Org. Chem., Vol. 67, No. 25, 2002

DDP-DBA Hybrids
F IGURE 5. Electronic absorption spectra of DDP 4 and its
corresponding CPD form 38.
F IGURE 4. Electronic absorption spectra of hybrids 3 and
32.
SCHEME 8 a
data, NICS and bond lengths, clearly demonstrate that
the DDP-fused ODA nucleus in 2 is considerably more
diatropic than the ODA nucleus in 1, fused with a DDP
1
and two benzenes. The experimental H NMR chemical
shifts of the internal methyls of the DDPs in 1 and 2 only
differ by 0.2 ppm, which is on the same order as
anisotropy-driven perturbations to these methyl shifts.
We conclude that such shift differences of less than 0.3
ppm for the internal methyls of the DDP nucleus are too
small to reliably measure the relative aromaticity of the
DDP nucleus and, subsequently, the annelating group.
Hybrids where both a benzene ring and a [14]DBA are
fused to the DDP allow for facile isomerization between
the pyrene and cyclophanediene isomers using different
light sources.
Exp er im en ta l Section
Gen er a l In for m a tion . 1H and 13C NMR spectra were
recorded on a 300 MHz (1H, 299.95 MHz; 13C, 75.43 MHz) or
360 MHz (1H, 360 MHz; 13C, 90.6 MHz) NMR spectrometer
and were obtained in CDCl3. Chemical shifts (δ) are expressed
in parts per million downfield from tetramethylsilane using
the residual chloroform (1H, 7.26 ppm; 13C, 77.0 ppm) as
internal standard. Coupling constants are expressed in hertz.
Et3N was distilled from CaH2 under a N2 atmosphere prior to
use. THF and Et2O were distilled from Na and benzophenone
under a N2 atmosphere prior to use. All other chemicals were
of reagent quality and used as obtained from the manufactur-
ers. Column chromatography was performed on reagent grade
silica gel (230-400 mesh). Precoated silica gel plates were used
for analytical (200 × 50 × 0.25 mm) and preparative (200 ×
200 × 1 mm) thin-layer chromatography. Reactions were
carried out in an inert atmosphere (dry N2 or Ar) when
necessary. All deprotected terminal alkynes were used directly
without further purification.
Gen er a l P r oced u r e A. Cou p lin g Acetylen es to Br om o-
DDP s. The bromo-DDP (1 equiv), PdCl2(PPh3)2 (0.04 equiv),
Pd(PPh3)4 (0.02 equiv), and CuI (0.14 equiv) were suspended
in Et3N and DMF (2:1 v/v, 0.15 M) in a glass pressure tube.
The acetylene (1.2 equiv per bromine) was added, and the
contents were degassed by three successive freeze-pump-
thaw cycles. The tube was then charged with N2 and sealed.
The mixture was heated to 100 °C for 24-48 h with stirring.
After cooling, the mixture was diluted into Et2O and washed
successively with saturated NH4Cl solution, H2O, and brine.
The organics were dried (MgSO4) and vacuum filtered through
silica gel. The solvent was evaporated, and the crude product
was purified by either column or preparative thin-layer
chromatography to give the final product in pure form.
a
Reagents and conditions: (a) NBS, DMF, CH2Cl2; (b) 1-ethyn-
yl-2-(triisopropylsilyl)ethynylbenzene, PdCl2(PPh3)2, Pd(PPh3)4,
CuI, DMF, Et3N, 100 °C; (c) Bu4NF, MeOH, THF; (d) CuCl,
pyridine, MeOH, THF.
Con clu sion s
The synthesis of mono- and bisfused DBA-DDP hy-
brids has been accomplished. Comparison of the interior
methyl resonances for the DDP core, its arene reso-
nances, and its calculated RAs all confirm the existence
of weak diatropic ring currents associated with the ODA
nucleus. In agreement with expectations, the calculated
J . Org. Chem, Vol. 67, No. 25, 2002 8807

Kimball et al.
Gen er a l P r oced u r e B. Clea va ge of Silyl P r otectin g
Gr ou p s Usin g Bu 4NF . The silyl-protected arylacetylene was
dissolved in THF and MeOH (5:1 v/v, 0.03 M). Bu4NF (1.0 M
in THF, 3 equiv per silyl group) was added and the solution
stirred overnight. The contents were diluted with Et2O,
washed with saturated NH4Cl solution and brine, dried
(MgSO4), and vacuum filtered through silica gel. After evapo-
ration, the crude desilylated product was used for subsequent
coupling.
1.69 (s, 18H), -3.82 (s, 6H); 13C NMR (CDCl3) δ 148.32, 137.85,
133.20, 124.10, 123.21, 122.30, 119.15, 36.30, 32.15, 31.87,
14.24; IR (KBr) ν 1362, 1339, 874, 673 cm-1; MS (CI) m/z 501
(M+ + H, correct isotope pattern). Anal. Calcd for C26H30Br2:
C, 62.17; H 6.02. Found: C, 62.84; H, 5.97. (About 3%
1
bromopyrene 8 was present by H NMR.)
4-ter t-Bu tyl-1-eth yn yl-2-(tr iisop r op ylsilyl)eth yn ylben -
zen e (9). A mixture of 4-tert-butyl-1-iodo-2-(triisopropylsilyl)-
ethynylbenzene18 (881 mg, 2.0 mmol), PdCl2(PPh3)2 (42 mg,
0.06 mmol), CuI (19 mg, 0.10 mmol), and Et3N (10 mL)
was degassed by three freeze-pump-thaw cycles. Ethynyltri-
methylsilane (0.56 mL, 4.0 mmol) was added and the mixture
stirred at 40 °C for 10 h. The reaction was diluted with hexanes
and filtered through a pad of Celite and silica gel. The filtrate
was concentrated and the residue redissolved in THF (25 mL)
and MeOH (5 mL). K2CO3 (276 mg, 2.0 mmol) was added and
the mixture stirred at rt for 4 h. The reaction was diluted with
hexanes and washed repeatedly with water and brine. The
organic layer was dried (MgSO4), filtered, and concentrated.
Purification by column chromatography (hexanes) gave 9 (568
mg, 84%) as a yellow oil: 1H NMR (CDCl3) δ 7.47 (d, J ) 2.1
Hz, 1H), 7.42 (d, J ) 8.1 Hz, 1H), 7.29 (dd, J ) 8.1, 2.1 Hz,
1H), 3.20 (s, 1H), 1.30 (s, 9H), 1.15 (s, 21H); 13C NMR (CDCl3)
δ 151.68, 132.21, 129.18, 126.21, 125.37, 122.17, 105.38, 94.35,
82.40, 80.29, 34.69, 30.99, 18.71, 11.31; IR (neat) ν 3304, 3062,
2159, 1463 cm-1; HRMS m/z calcd for C23H34Si, 338.2430,
found 338.2423.
Mon o[14]DBA-DDP P olyyn e 10. Dibromide 5 (45 mg,
0.09 mmol), diyne 9 (140 mg, 0.41 mmol), PdCl2(PPh3)2 (5.2
mg, 0.007 mmol), Pd(PPh3)4 (4.3 mg, 0.004 mmol), CuI (3 mg,
0.02 mmol), Et3N (1 mL), and DMF (2 mL) were reacted using
general procedure A. Column chromatography (petroluem
ether) gave 10 (80 mg, 88%) as a tan oil: 1H NMR (CDCl3) δ
9.05 (s, 2H), 8.46 (s, 2H), 8.39 (s, 2H), 7.63 (d, J ) 8.1 Hz,
2H), 7.55 (d, J ) 1.8 Hz, 2H), 7.29 (dd, J ) 8.1, 1.8 Hz, 2H),
1.66 (s, 18H), 1.34 (s, 18H), 0.94 (s, 21H), 0.93 (s, 21H), -3.65
(s, 6H); 13C NMR (CDCl3) δ 150.46, 147.53, 138.33, 137.12,
132.68, 129.41, 125.34, 125.06, 124.42, 123.84, 122.08, 120.43,
117.17, 106.54, 96.59, 93.87, 91.78, 36.14, 34.64, 31.80, 31.10,
18.66, 11.25; IR (neat) ν 3035, 2958, 2197, 2153 cm-1; UV-
vis (CH2Cl2) λmax (log ꢀ) 380 (4.65), 414 (4.67), 484 (3.90), 683
(3.42) nm; HRMS m/z calcd for C72H96Si2 1016.7051, found
1016.7032.
2,7-Di-ter t-bu tyl-4-tr im eth ylsilyl-tr a n s-10b,10c-dim eth -
yl-10b,10c-d ih yd r op yr en e (7). BuLi (4.0 mL, 2.5 M in
hexanes) was added dropwise by syringe to vacuum-dried
bromopyrene 617 (626 mg, 1.5 mmol) in dry THF (120 mL) at
-78 °C. The initially green solution rapidly turned brown. The
mixture was stirred for 7 min, and then freshly distilled Me3-
SiCl (3.0 mL, 28 mmol) was added carefully by syringe. Cooling
was then stopped, and the reaction mixture gradually turned
green. After the mixture was stirred for 30 min at 20 °C,
hexanes and water were added. The organic phase was washed
successively with 10% aq NaHCO3 solution and water, dried
(MgSO4), and evaporated to give a green solid containing a
ca. 7:1 mixture of 7 and 6. The crude material was purified by
chromatography on silica gel (hexanes) deactivated with 5%
water. The leading green band was collected, and each fraction
evaporated separately and analyzed by NMR. The fractions
with over 96 mol % 7 were combined to give 292 mg. The
remaining fractions were evaporated and rechromatographed
to yield an additional 186 mg. The total purified yield was 478
mg (78%). Recrystallization (cyclohexane) of 7 gave green
crystals: mp 186-188 °C; 1H NMR (CDCl3) δ 8.75 (d, J ) 1.0
Hz, 1H), 8.66 (s, 1H), 8.51 (s, 1H), 8.49 (br s, 1H), 8.48 (br s,
1H), 8.40 (ABm, J ) 7.7 Hz, 1H), 8.38 (ABm, 1H), 1.68 (s, 9H),
1.67 (s, 9H), 0.67 (s, 9H), -4.02 (s, 3H), -4.05 (s, 3H); 13C NMR
(CDCl3) δ 145.26, 145.23, 141.01, 135.48, 136.22, 135.65,
133.08, 129.54, 122.54, 122.33, 121.55, 121.20, 120.74, 120.06,
36.09, 35.90, 31.95, 30.30, 29.24, 14.57, 14.33, 1.04; IR (KBr)
ν 1382, 1358, 1342, 1249, 1227, 874, 849, 835, 669 cm-1; MS
(CI) m/z (rel intens) 417 (100, M+ + H). Anal. Calcd for C29H40
Si: C, 83.59; H 9.68. Found: C, 83.56; H, 9.65.
-
4,5-Dib r om o-2,7-d i-ter t-b u t yl-9-t r im et h ylsilyl-tr a n s-
10b,10c-d im eth yl-10b,10c-d ih yd r op yr en e (8). NBS (334
mg, 1.9 mmol) in dry DMF (40 mL) was added dropwise at 0
°C to a solution of 7 (253 mg, 0.61 mmol) in dry CH2Cl2 (200
mL) under argon. After the addition, the ice bath was removed
and the mixture allowed to stir for 20 h. The solution was
diluted with hexanes, and then water was added with rapid
stirring. After the solution was stirred for 2 min, the organic
phase was washed with water, dried (MgSO4), and concen-
trated. The residue was taken up in hexanes/CH2Cl2 (1:1) and
filtered through silica gel deactivated with 5% water. Removal
of the solvent furnished 8 (330 mg, 95%). Recrystallization
from cyclohexane gave green crystals: mp 203-206 °C; 1H
NMR (CDCl3) δ 8.90 (d, J ) 1.1 Hz, 1H), 8.88 (d, J ) 1.3 Hz,
1H), 8.75 (d, J ) 0.9 Hz, 1H), 8.63 (s, 1H), 8.50 (br s, 1H), 1.69
(s, 9H), 1.68 (s, 9H), 0.66 (s, 9H), -3.76 (s, 3H), -3.78 (s, 3H);
13C NMR (CDCl3) δ 148.43, 148.30, 142.11, 137.03, 135.04,
134.98, 132.83, 131.22, 123.02, 122.87, 122.84, 122.31, 118.91,
118.67, 36.47, 36.28, 33.20, 32.11, 31.80, 14.53, 14.34, 0.92;
Mon o[14]DBA-DDP 1. Polyyne 10 (66 mg, 0.065 mmol)
was treated with Bu4NF (1.5 mL, 1.5 mmol) in THF (15 mL)
and MeOH (1 mL) using general procedure B. The desilylated
polyyne was dissolved in THF (8 mL) and added over 8 h to a
slurry of CuCl (400 mg, 4.04 mmol), MeOH (2 mL), and
pyridine (10 mL) under air at rt. After the solution was stirred
for 48 h, the volatiles were evaporated and the crude material
was redissolved in CH2Cl2 and vacuum filtered through silica
gel. Purification by column chromatography (6:1 petroleum
ether/CH2Cl2) gave 1 (14 mg, 30%) as a dark red powder: mp
> 350 °C; 1H NMR (CDCl3) δ 9.54 (s, 2H), 8.59 (s, 2H), 8.48 (s,
2H), 8.22 (d, J ) 8.1 Hz, 2H), 7.65 (d, J ) 1.5 Hz, 2H), 7.61
(dd, J ) 8.1, 1.5 Hz, 2H), 1.82 (s, 18H), 1.41 (s, 18H), -3.71
(s, 6H); 13C NMR (CDCl3) δ 150.90, 147.95, 139.13, 138.75,
132.50, 128.08, 126.27, 126.14, 124.07, 122.31, 121.95, 121.48,
115.04, 99.61, 93.81, 87.14, 80.09, 36.53, 34.94, 32.12, 31.14,
IR (KBr) ν 1362, 1337, 1248, 965, 873, 848, 837, 749, 662 cm-1
;
MS (CI) m/z 573 (M+ + H, correct isotope pattern). Anal. Calcd
15.02; IR (KBr) ν 3046, 2961, 2924, 2865, 2207, 2160 cm-1
;
for C29H38Br2Si; C, 61.63; H 6.67. Found: C, 61.72; H, 6.74.
UV-vis (CH2Cl2) λmax (log ꢀ) 313 (4.86), 359 (4.49), 407 (4.89),
437 (4.98), 506 (4.13), 577 (2.93), 636 (3.10), 704 (3.96) nm;
HRMS m/z calcd for C54H54 702.4226, found 702.4237.
4,5-Dibr om o-2,7-d i-ter t-bu tyl-tr a n s-10b,10c-d im eth yl-
10b,10c-d ih yd r op yr en e (5). A solution of 8 (93 mg, 0.16
mmol) in THF (20 mL) was refluxed with Bu4NF (1.5 mL, 1.0
M in THF) under argon for 24 h. After cooling, the mixture
was diluted with hexanes and washed with water. The organic
phase was dried (MgSO4) and concentrated. The residue was
taken up in hexane and CH2Cl2 (6:1 v/v) and filtered through
silica gel deactivated with 5% water. The first band was
collected and recrystallized (cyclohexane) to yield 5 (68 mg,
Mon o[14]a lk en e-DDP P olyyn e 13. Dibromo-DDP 5 (40
mg, 0.08 mmol), enediyne 1220 (79 mg, 0.34 mmol), PdCl2-
(PPh3)2 (3.4 mg, 0.0048 mmol), Pd(PPh3)4 (2.8 mg, 0.0024
mmol), CuI (1.7 mg, 0.0088 mmol), Et3N (1 mL), and DMF (2
mL) were reacted using general procedure A. Purification by
column chromatography (19:1 petroleum ether/CH2Cl2) gave
13 (15 mg, 23%) as a viscous, dark red oil: 1H NMR (CDCl3)
δ 8.95 (s, 2H), 8.46 (s, 2H), 8.39 (s, 2H), 6.41 (d, J ) 11.1 Hz,
2H), 6.00 (d, J ) 11.1 Hz, 2H), 1.68 (s, 18H), 1.25 (s, 42H),
1
84%) as green crystals: mp 198-200 °C; H NMR (CDCl3) δ
8.96 (d, J ) 1.3 Hz, 2H), 8.54 (d, J ) 1.3 Hz, 2H), 8.45 (s, 2H),
8808 J . Org. Chem., Vol. 67, No. 25, 2002

DDP-DBA Hybrids
-3.71 (s, 6H); 13C NMR (CDCl3) δ 147.93, 138.51, 137.24,
124.16, 122.31, 121.27, 120.30, 118.39, 116.09, 104.54, 99.36,
96.69, 95.31, 36.16, 31.74, 18.59, 15.09, 11.17; IR (neat) ν 3037,
2956, 2864, 2181, 2139 cm-1; UV-vis (CH2Cl2) λmax (log ꢀ) 262
(4.32), 313 (4.08), 384 (4.45), 413 (4.48), 490 (3.73), 687 (3.12)
nm; HRMS m/z calcd for C56H76Si2 804.5486, found 804.5479.
370 (4.76), 407 (4.70), 483 (3.90), 684 (3.47) nm; HRMS m/z
calcd for C36H48Si2 536.3295, found 536.3293.
Bis(DDP )-Deh yd r o[12]a n n u len e 21 a n d Tr is(DDP )-
Deh yd r o[18]a n n u len e 22. Diyne 20 (38 mg, 0.07 mmol) was
dissolved in THF (2 mL) and MeOH (0.1 mL) and then treated
with Bu4NF (0.5 mL, 1.0 M in THF) using general procedure
B. After workup, the crude desilylated diyne was dissolved in
THF (2 mL) and DMSO (2 mL) and added to an argon-
degassed mixture of 1-bromoethynyl-2-(triisopropylsilyl)-
ethynylbenzene8b (72 mg, 0.2 mmol), Pd(dba)2 (3.5 mg, 0.006
mmol), CuI (1.0 mg, 0.005 mmol), LiI (7.5 mg, 0.04 mmol), and
DMSO (2 mL) using the procedure of Vasella.24 The reactants
were stirred for 5 min at rt, and then 1,2,2,6,6-pentameth-
ylpiperidine (87 mg, 0.56 mmol) was added. After 48 h, Et2O
(35 mL) and 10% aq NH4Cl solution (10 mL) were added. The
organic layer was washed with water, dried (MgSO4), filtered,
and concentrated. Purification by preparative TLC (4:1 petro-
leum ether/CH2Cl2) gave 21 (5 mg, 19%) as an unstable red
semisolid and 22 (12 mg, 44%) as a red solid. Data for 21: 1H
NMR (CDCl3) δ 8.66 (br s, 4H), 8.33 (br s, 4H), 8.27 (d, J )
2.1 Hz, 4H), 1.70 (s, 36H), -3.24 (s, 6H), -3.25 (s, 6H); IR
(neat) ν 3036, 2963, 2157, 1467, 1261 cm-1; UV-vis (CH2Cl2)
λmax (log ꢀ) 381 (5.02), 435 (4.79), 482 (4.96), 536 (4.56), 703
Mon o[14]a lk en e-DDP 2. Polyyne 13 (15 mg, 0.019 mmol)
was treated with Bu4NF (1.5 mL, 1.5 mmol) in MeOH (0.7 mL)
and THF (6 mL) using general procedure B. The desilylated
product was dissolved in THF (3 mL) and added over 8 h to a
slurry of CuCl (38 mg, 0.37 mmol), MeOH (1 mL), and pyridine
(8 mL) under air at rt. After the solution was stirred for an
additional 48 h, the volatiles were evaporated and the contents
were redissolved in CH2Cl2 and vacuum filtered through silica
gel. Purification by preparative TLC (9:1 petroleum ether/CH2-
Cl2) gave 2 (3.5 mg, 38%) as an unstable red oil: 1H NMR
(CDCl3) δ 9.65 (s, 2H), 8.69 (s, 2H), 8.58 (s, 2H), 7.66 (d, J )
9.0 Hz, 2H), 6.61 (d, J ) 9.0 Hz, 2H), 1.80 (s, 18H), -3.91 (s,
6H); IR (neat) ν 3038, 2156, 2109 cm-1; UV-vis (CH2Cl2) λmax
(log ꢀ) 312 (4.49), 400 (4.49), 443 (4.44), 718 (3.74) nm; MS
(FAB) m/z (rel intens) 491.2 (50, M+ + H+), 282.3 (100, M+
Na - C18H15).
+
Mon o[14]a lk a n e-DDP P olyyn e 18. Dibromo 5 (20 mg,
0.04 mmol), diyne 1721 (180 mg, 1.2 mmol), PdCl2(PPh3)2 (3.4
mg, 0.0048 mmol), Pd(PPh3)4 (2.8 mg, 0.0024 mmol), CuI (1.7
mg, 0.0088 mmol), Et3N (1 mL), and DMF (2 mL) were reacted
using general procedure A. Purification by column chroma-
tography (9:1 petroleum ether/CH2Cl2) gave 18 (23 mg, 92%)
as a dark yellow oil: 1H NMR (CDCl3) δ 8.94 (s, 2H), 8.46 (s,
2H), 8.38 (s, 2H), 3.06-3.00 (m, 4H), 2.85-2.80 (m, 4H), 1.68
(s, 18H), 0.17 (s, 18H), -3.80 (s, 6H); 13C NMR (CDCl3) δ
147.47, 138.21, 136.92, 123.79, 121.87, 120.13, 116.70, 105.67,
96.60, 85.68, 80.71, 36.17, 31.84, 20.88, 20.70, 14.92, 0.10; IR
(neat) ν 3036, 2959, 2923, 2864, 2176 cm-1; UV-vis (CH2Cl2)
λmax (log ꢀ) 273 (3.87), 365 (4.56), 405 (4.49), 479 (3.52), 500
(3.52), 681 (2.82) nm; HRMS m/z calcd for C44H56Si2 640.3921,
found 640.3928.
(3.80), 744 (4.15) nm; HRMS m/z calcd for
C60H60 + H
781.4773, found 781.4795. Data for 22: 1H NMR (CDCl3) δ 9.29
(s, 6H), 8.57 (s, 6H), 8.48 (s, 6H), 1.84 (s, 54H), -3.56 (s, 9H),
-3.57 (s, 9H); IR (neat) ν 3036, 2924, 2177, 1464, 1070 cm-1
;
UV-vis (CH2Cl2) λmax (log ꢀ) 356 (4.94), 460 (5.16), 539 (4.80),
719 (4.49) nm; HRMS m/z calcd for C90H90 + H 1171.7121,
found 1171.7141. Limited solubility of 21 and 22 in organic
solvents precluded 13C NMR spectroscopy.
4,5,9,10-Tetr a br om o-2,7-d i-ter t-bu tyl-tr a n s-10b,10c-d i-
m et h yl-10b ,10c-d ih yd r op yr en e (30). A solution of Br2
(2.05 g, 12.8 mmol) in CCl4 (160 mL) was added dropwise to a
solution of dihydropyrene 1135 (1.10 g, 3.20 mmol) in CCl4 (200
mL) at 0 °C over 1 h. The mixture was stirred for an additional
1 h and then poured into ice-water. The mixture was
extracted with CH2Cl2 (300 mL), and the organic layer was
washed with water, dried (MgSO4), and concentrated. Recrys-
tallization (hexane) yielded 30 (2.01 g, 95%) as green crys-
tals: mp 227-229 °C (lit.35 mp 228-230 °C).
Bis[14]p olyyn e-DDP 31. Tetrabromo 30 (73 mg, 0.11
mmol), 1-ethynyl-2-(triisopropylsilyl)ethynylbenzene8b (244
mg, 0.86 mmol), PdCl2(PPh3)2 (6 mg, 0.009 mmol), Pd(PPh3)4
(4 mg, 0.004 mmol), CuI (10 mg, 0.053 mmol), Et3N (1.5 mL),
and DMF (1.5 mL) were reacted using general procedure A.
Purification by preparative TLC (7:1 hexanes/CH2Cl2) gave 31
(86 mg, 53%) as a brown powder: mp 271.0-272.4 °C; 1H NMR
(CDCl3) δ 9.07 (s, 4H), 7.73-7.70 (m, 4H), 7.59-7.56 (m, 4H),
7.34-7.25 (m, 8H), 1.66 (s, 18H), 0.94 (s, 84H), -3.39 (s, 6H);
IR (neat) ν 3061, 2924, 2864, 2155, 1465 cm-1; MS (FAB) m/z
(rel intens) 1466 (42, M+). Limited solubility of 31 in organic
solvents precluded 13C NMR spectroscopy.
Mon o[14]a lk a n e-DDP 16. Polyyne 18 (23 mg, 0.036
mmol) was combined with K2CO3 (276 mg, 2 mmol), MeOH (2
mL), and THF (7 mL) and stirred overnight at rt. The mixture
was diluted with Et2O and washed with H2O. The organic layer
was dried (MgSO4), vacuum filtered through silica gel, and
concentrated. The crude product was then dissolved in THF
(3 mL) and added over 8 h to a slurry of CuCl (50 mg, 0.51
mmol), MeOH (2 mL), and pyridine (6 mL) under air at rt.
After the solution was stirred for an additional 48 h, the
volatiles were evaporated and the crude solid was redissolved
in CH2Cl2 and vacuum filtered through silica gel. Purification
by preparative TLC (3:1 petroleum ether/CH2Cl2) provided 16
(3 mg, 17%) as a yellow semisolid: 1H NMR (CDCl3) δ 9.06 (s,
2H), 8.46 (s, 2H), 8.38 (s, 2H), 3.22 (t, J ) 6.6 Hz, 4H), 2.68 (t,
J ) 6.6 Hz, 4H), 1.69 (s, 18H), -3.77 (s, 6H); 13C NMR (CDCl3)
δ 147.44, 138.64, 138.09, 123.71, 121.85, 120.74, 120.66,
116.41, 96.75, 83.50, 81.17, 70.44, 36.15, 31.85, 29.69, 19.78,
14.90; IR (neat) ν 3040, 2955, 2924, 2853, 2257 cm-1; UV-vis
(CH2Cl2) λmax (log ꢀ) 369 (4.73), 405 (4.65), 481 (3.81), 500
(3.81), 682 (3.40) nm; HRMS m/z calcd for C38H38 494.2974,
found 494.2970.
Bis[14]DBA-DDP 3. Polyyne 31 (200 mg, 0.14 mmol) was
dissolved in THF (10 mL) and MeOH (1 mL) and then treated
with Bu4NF (2.0 mL, 1.0 M in THF) using general procedure
B. The deprotected polyyne was dissolved in pyridine (5 mL)
and THF (3 mL) and then added slowly over 8 h to a slurry of
CuCl (166 mg, 1.68 mmol) and pyridine (10 mL) at rt under
house air. After 48 h, the solvent was evaporated and the
residue was redissolved in CH2Cl2. The slurry was filtered
through silica gel and the filtrate concentrated to give a dark
semisolid. Purification by preparative TLC (2:1 hexanes/CH2-
Cl2) gave 3 (22 mg, 16%) as a red-brown powder: mp > 350
4,5-Bis(t r im et h ylsilylet h yn yl)-2,7-d i-ter t-b u t yl-tr a n s-
10b,10c-d im eth yl-10b,10c-d ih yd r op yr en e (20). Dibromo-
DDP 5 (50 mg, 0.1 mmol), ethynyltrimethylsilane (0.25 mL,
1.8 mmol), PdCl2(PPh3)2 (4 mg, 0.0057 mmol), Pd(PPh3)4 (2.3
mg, 0.0020 mmol), CuI (3 mg, 0.016 mmol), Et3N (1 mL), and
DMF (2 mL) were reacted using general procedure A. Purifica-
tion by column chromatography (9:1 hexanes/CH2Cl2) gave 20
(33 mg, 61%) as a brown semisolid: 1H NMR (CDCl3) δ 9.02
(d, J ) 1.4 Hz, 2H), 8.47 (d, J ) 1.4 Hz, 2H), 8.39 (s, 2H), 1.69
(s, 18H), 0.45 (s, 18H), -3.76 (s, 6H); 13C NMR (CDCl3) δ
148.12, 138.69, 137.85, 124.19, 122.19, 120.53, 115.98, 104.01,
102.85, 36.25, 31.75, 15.05, 0.43; IR (neat) ν 3034, 2961, 2925,
2901, 2864, 2143 cm-1; UV-vis (CH2Cl2) λmax (log ꢀ) 278 (4.04),
1
°C; H NMR (CDCl3) δ 9.65 (s, 4H), 8.36 (d, J ) 6.9 Hz, 4H),
7.70-7.65 (m, 8H), 7.55-7.50 (m, 4H), 1.95 (s, 18H), -3.33 (s,
6H); IR (KBr) ν 3059, 2962, 2924, 2865, 2220, 2161, 1474, 752
cm-1; UV-vis (CH2Cl2) λmax (log ꢀ) 277 (4.64), 300 (4.66), 320
(4.64), 440 (4.67), 470 (4.87), 540 (4.20), 616 (3.42), 679 (3.43),
758 (4.03) nm; MS (MALDI-TOF) m/z (rel intens) 837.90 (52,
M+). Limited solubility of 3 in organic solvents precluded 13C
NMR spectroscopy.
J . Org. Chem, Vol. 67, No. 25, 2002 8809

Kimball et al.
4,5,9,10-Tetr a k is[d im eth yl(1,1,2-tr im eth yp r op yl)silyl-
eth yn yl]-2,7-di-ter t-bu tyl-tr a n s-10b,10c-dim eth yl-10b,10c-
d ih yd r op yr en e (33). Tetrabromo 30 (350 mg, 0.530 mmol),
dimethylethynyl(1,1,2-trimethylpropyl)silane (897 mg, 5.33
mmol), PdCl2(PPh3)2 (25 mg, 0.036 mmol), Pd(PPh3)4 (21 mg,
0.018 mmol), CuI (10 mg, 0.053 mmol), Et3N (3.5 mL), and
DMF (3.5 mL) were reacted using general procedure A.
Purification by preparative TLC (9:1 hexanes/CH2Cl2) gave 33
(177 mg, 33%) as a green-black powder: mp > 350 °C; 1H NMR
(CDCl3) δ 9.02 (s, 4H), 1.91 (septet, J ) 6.9 Hz, 4 H), 1.67 (s,
18H), 1.15 (s, 24H), 1.04 (d, J ) 6.9 Hz, 24 H), 0.45 (s, 12H),
0.43 (s, 12H), -3.53 (s, 6H); 13C NMR (CDCl3) δ 149.70, 139.07,
122.22, 117.99, 104.49, 103.43, 36.49, 34.59, 31.75, 30.62,
23.63, 21.06, 18.86, 15.72, -1.81; IR (KBr) ν 2959, 2925, 2864,
2136, 1249, 821, 772 cm-1; UV-vis (CH2Cl2) λmax (log ꢀ) 265
(4.43), 288 (4.14), 295 (4.12), 307 (4.18), 314 (4.13), 327 (4.16),
405 (4.13), 432 (4.22), 504 (3.21), 728 (2.84) nm; HRMS m/z
calcd for C66H105Si4 1009.7293, found 1009.7274.
preparative TLC (9:1 hexanes/CH2Cl2) gave 35 (27 mg, 87%)
as a deep red powder: mp 241.0-243.1 °C; H NMR (CDCl3)
1
δ 9.18 (s, 4H), 7.82 (d, J ) 7.2 Hz, 8H), 7.50-7.40 (m, 12H),
1.79 (s, 18H), -3.32 (s, 6H); 13C NMR (CDCl3) δ 138.51, 131.60,
128.57, 128.29, 124.08, 122.07, 117.98, 99.18, 88.97, 36.53,
31.83, 16.06; IR (KBr) ν 3081, 2961, 2920, 2855, 1493, 759,
749 cm-1; UV-vis (CH2Cl2) λmax (log ꢀ) 292 (4.30), 423 (4.79),
449 (4.91), 515 (4.19), 601 (2.95), 670 (2.99), 740 (3.92) nm;
HRMS m/z calcd for C58H48 744.3756, found 744.3769.
tr a n s-4,5-Dib r om o-2,7-d i-ter t-b u t yl-12c,12d -d ih yd r o-
12c,12d -d im eth ylben zo[e]p yr en e (36). A solution of benzo-
DDP 2717 (285 mg, 0.72 mmol) in dry CH2Cl2 (200 mL) was
prepared under argon in the dark and cooled in an ice bath.
NBS (257 mg, 1.44 mmol) in dry DMF (40 mL) was added
slowly with stirring. The reaction was allowed to warm to 20
°C and stirred for 2 h. The mixture was poured into hexanes
and washed with water. The organic phase was dried (MgSO4)
and concentrated. The residue was purified from fluorescent
pyrenes by chromatography over silica gel (9:1 hexanes/CH2-
Cl2) deactivated with 5% water. Repeating the chromatography
three additional times yielded 36 (191 mg, 48%) as intense
purple crystals from cyclohexane: mp 187-189 °C dec; 1H
NMR (CDCl3) δ 8.69-8.64 (AA′XX′m, 2H), 8.21 (d, J ) 1.3 Hz,
2H), 7.73 (d, J ) 1.3 Hz, 2H), 7.65-7.60 (AA′XX′m, 2H), 1.49
(s, 18H), -1.30 (s, 6H); 13C NMR (CDCl3) δ 148.67, 136.16,
135.71, 129.15, 126.67, 124.69, 120.15, 117.51, 117.04, 39.13,
35.87, 30.37, 17.34; IR (KBr) ν 866, 754, 610 cm-1; MS (CI)
m/z 551 (M+ + H, correct isotope pattern). Anal. Calcd for
Bis[18]p olyyn e-DDP 34. Tetrayne 33 (50 mg, 0.05 mmol)
was dissolved in THF (2 mL) and MeOH (0.1 mL) and then
treated with Bu4NF (0.5 mL, 1.0 M in THF) using general
procedure B. After workup, the desilylated tetrayne (∼19 mg,
0.05 mmol) dissolved in THF (2 mL) and DMSO (2 mL) was
added to an argon-degassed mixture of 1-bromoethynyl-2-
(triisopropylsilyl)ethynylbenzene8b (72 mg, 0.2 mmol), Pd(dba)2
(3.5 mg, 0.006 mmol), CuI (1.0 mg, 0.005 mmol), LiI (7.5 mg,
0.04 mmol), and DMSO (2 mL) using the procedure of
Vasella.24 The reactants were stirred for 5 min at rt, and then
1,2,2,6,6-pentamethylpiperidine (87 mg, 0.56 mmol) was added.
After 48 h, Et2O (35 mL) and 10% aq NH4Cl solution (10 mL)
were added. The organic layer was washed with H2O, dried
(MgSO4), filtered, and concentrated. Purification by prepara-
tive TLC (4:1 petroleum ether/CH2Cl2) gave 34 (62 mg, 80%)
as a black semisolid: 1H NMR (CDCl3) δ 9.02 (s, 4H), 7.64-
7.61 (m, 4H), 7.55-7.52 (m, 4H), 7.35-7.28 (m, 8H), 1.73 (s,
18H), 1.14 (s, 84H), -3.39 (s, 6H); 13C NMR (CDCl3) δ 151.47,
140.52, 133.07, 132.43, 128.57, 127.92, 127.04, 125.15, 122.64,
117.65, 104.67, 96.18, 84.08, 83.45, 81.09, 78.55, 36.59, 31.73,
18.71, 16.15, 11.29; IR (KBr) ν 3060, 2943, 2942, 2864, 2202,
2156, 1462, 756 cm-1; MS (FAB) m/z (rel intens) 933.3 (36,
C
30H32 Br2: C, 65.23; H, 5.84. Found: C, 65.33; H, 5.89.
Ben zo-DDP -[14]DBA P olyyn e 37. Dibromo-DDP 36 (40
mg, 0.072 mmol), 1-ethynyl-2-(triisopropylsilyl)ethynylbenzene8b
(51 mg, 0.18 mmol), PdCl2(PPh3)2 (5.2 mg, 0.0074 mmol), Pd-
(PPh3)4 (4.3 mg, 0.0037 mmol), CuI (3 mg, 0.016 mmol), Et3N
(1 mL), and DMF (3 mL) were reacted using general procedure
A. Column chromatography (9:1 hexanes/CH2Cl2) provided 37
(53 mg, 77%) as a dark red oil: 1H NMR (CDCl3) δ 8.70 (br s,
2H), 8.23 (s, 2H), 7.99 (s, 2H), 7.64-7.61 (m, 2H), 7.60-7.57
(m, 2H), 7.53-7.50 (m, 2H), 7.24-7.16 (m, 4H), 1.94 (s, 18H),
1.02 (s, 21H), 1.01 (s, 21H), -1.24 (s, 6H); 13C NMR (CDCl3) δ
132.72, 129.28, 127.78, 127.23, 126.95, 126.32, 125.43, 124.54,
118.80 (br), 117.67 (br), 114.90, 105.91, 95.52 (br), 94.67, 36.36,
30.38, 18.71, 18.12, 11.29; IR (neat) ν 3061, 2960, 2864, 2197,
2955 cm-1; UV-vis (CH2Cl2) λmax (log ꢀ) 239 (5.01), 271 (5.13),
362 (4.43), 401 (4.63), 420 (4.75), 527 (3.76) nm; HRMS m/z
calcd for C68H83Si2 955.6033, found 955.6058.
-
M+), 918.3 (M+ Me), 903.3 (M+ - 2Me), 176 (100).
Bis[18]DBA-DDP 32. Polyyne 34 (45 mg, 0.04 mmol) was
dissolved in THF (5 mL) and MeOH (0.5 mL) and then treated
with Bu4NF (1.0 mL, 1.0 M in THF) using general procedure
B. After workup, the deprotected polyyne was dissolved in THF
(6 mL) and added slowly over 8 h to a slurry of Cu(OAc)2 (213
mg, 1.1 mmol) in THF (3 mL) and pyridine (9 mL) at rt under
house air. After 48 h, the solvent was evaporated and the
residue redissolved in CH2Cl2. The solution was filtered
through silica gel and the filtrate concentrated. Purification
of the dark residue by column chromatography (4:1:1 petro-
leum ether/CH2Cl2/THF) gave 32 (13 mg, 47%) as a dark violet-
Ben zo-DDP -[14]DBA 4. Polyyne 37 (45 mg, 0.047 mmol)
was treated with Bu4NF (1 mL, 1.0 M in THF) in MeOH (0.7
mL) and THF (20 mL) using general procedure B. After
workup, the desilylated product was dissolved in THF (9 mL)
and added over 8 h to a slurry of CuCl (400 mg, 4.0 mmol),
MeOH (5 mL), and pyridine (15 mL) under air at rt. After the
solution was stirred for an additional 48 h, the volatiles were
evaporated and the residue was dissolved in CH2Cl2 and
vacuum filtered through silica gel. Purification by preparative
TLC (4:1 petroleum ether/CH2Cl2) gave 4 (27 mg, 90%) as a
dark purple powder: mp 197 °C dec; 1H NMR (CDCl3) δ 8.77-
8.74 (m, 2H), 8.36 (s, 2H), 8.31 (s, 2H), 7.97 (d, J ) 7.6 Hz,
2H), 7.70-7.67 (m, 2H), 7.47-7.40 (m, 4H), 7.31 (t, J ) 7.6
Hz, 2H), 1.62 (s, 18H), -1.32 (s, 6H); 13C NMR (CDCl3) δ
148.84, 144.27, 137.82, 132.93, 131.54, 129.50, 129.42, 129.05,
127.64, 126.95, 124.89, 122.69, 119.00, 117.95, 113.03, 98.09,
94.04, 87.18, 80.66, 37.02, 30.99, 18.09; IR (neat) ν 3060, 2961,
2924, 2864, 2165 cm-1; UV-vis (CH2Cl2) λmax (log ꢀ) 230 (4.94),
298 (4.74), 319 (4.76), 439 (4.79), 550 (3.83) nm; HRMS m/z
calcd for C50H40 640.3130, found 640.3118.
Ben zo-CP D-[14]DBA 38. To an NMR tube were added 4
(8 mg, 0.012 mmol) and CDCl3 (1.0 mL). The solution was
irradiated in front of an overhead projector for 5 min, during
which the dark green-brown solution turned deep red: 1H
NMR (CDCl3) δ 7.92-7.89 (m, 2H), 7.78-7.71 (m, 4H), 7.67
(d, J ) 1.8 Hz, 2H), 7.54-7.51 (m, 4H), 7.46-7.44 (m, 2H),
6.97 (d, J ) 1.8 Hz, 2H), 1.34 (s, 6H), 1.33 (s, 18H); 13C NMR
(CDCl3) δ 150.84, 144.18, 140.28, 139.24, 138.49, 133.21,
1
black powder: mp > 350 °C; H NMR (CDCl3) δ 9.18 (s, 4H),
7.84-7.81 (m, 4H), 7.71-7.68 (m, 4H), 7.49-7.41 (m, 8H), 1.84
(s, 18H), -3.49 (s, 6H); IR (KBr) ν 3058, 2958, 2926, 2904,
2867, 2189, 2133, 752 cm-1; UV-vis (CH2Cl2) λmax (log ꢀ) 293
(4.85), 305 (4.87), 326 (4.87), 455 (5.03), 476 (5.22), 544 (4.67),
624 (3.82), 693 (3.82), 767 (4.60) nm; MS (FAB) m/z (rel intens)
932 (15, M+). Limited solubility of 32 in organic solvents
precluded 13C NMR spectroscopy.
4,5,9,10-Tet r a (p h en ylet h yn yl)-2,7-d i-ter t-b u t yl-tr a n s-
10b,10c-d im eth yl-10b,10c-d ih yd r op yr en e (35). Tetrayne
33 (42 mg, 0.042 mmol) was dissolved in THF (8 mL) and
MeOH (0.5 mL) and treated with Bu4NF (0.5 mL, 1.0 M in
THF) using general procedure B. After workup, the crude
product was combined with iodobenzene (0.094 mL, 0.84
mmol), PdCl2(PPh3)2 (2 mg, 0.003 mmol), Pd(PPh3)4 (3 mg,
0.003 mmol), CuI (2 mg, 0.012 mmol), and Et3N (10 mL). The
mixture was degassed by three successive freeze-pump-thaw
cycles, flushed with N2, and stirred at 60 °C for 48 h. After
cooling, the solvent was evaporated and the residue was
redissolved in Et2O. The solution was vacuum filtered through
Celite and silica gel and then concentrated. Purification by
8810 J . Org. Chem., Vol. 67, No. 25, 2002

DDP-DBA Hybrids
129.27, 129.71, 129.49, 129.37, 128.90, 128.86, 128.64, 128.28,
126.08, 122.47, 97.88, 96.97, 86.80, 80.77, 34.59, 31.60, 19.08;
UV-vis (CH2Cl2) λmax (log ꢀ) 230 (4.96), 307 (4.78), 320 (4.80),
418 (4.41), 437 (4.45).
Su p p or tin g In for m a tion Ava ila ble: Calculated bond
lengths and bond alternations for the DDP nucleus of 1, 2,
and 26 (Table S1), calculated bond lengths for the ODA nucleus
of 1, 2, 14, 25, and 26 (Table S2), calculated and experimental
1H and 13C NMR chemical shifts for 1, 2, 14, 25, and 26 (Tables
S3 and S4), Cartesian coordinates of 1, 2, 14, 25, and 26
optimized using the B3LYP/6-31G* method, and 13C NMR
spectra for compounds 1, 4, 9-10, 13, 16, 18, 20, 33-35, and
37. This material is available free of charge via the Internet
at http://pubs.acs.org.
Ack n ow led gm en t. We thank the Petroleum Re-
search Fund (M.M.H.), administered by the American
Chemical Society, the Natural Sciences and Engineering
Research Council of Canada (R.H.M.), the University
of Idaho for a Seed Grant (R.V.W.), and The Camille
and Henry Dreyfus Foundation (Teacher-Scholar Award
1998-2003 to M.M.H.) for financial support.
J O020462Q
J . Org. Chem, Vol. 67, No. 25, 2002 8811