Diatropicity of 3,4,7,8,9,10,13,14-octadehydro[14]annulenes: A combined experimental and theoretical investigation

Article abstract of DOI:10.1021/jo020463i

The synthesis and study of a series of octadehydro[14]annulenes is described. The aromaticity of these annulenes was investigated through examination of experimental data from arene-fused systems as well as calculated nucleus-independent chemical shifts (NICS) and bond lengths. Benzene ring fusion to the parent system results in a stepwise loss in aromaticity as the number of fused rings is increased from one to two to three. This decrease in annulenic ring current is manifested in the alkene proton chemical shifts (0-2 benzenes) as well as the NICS (0-3 benzenes). Comparison of isomeric thiophene-fused annulenes shows further evidence of ring current competition as these allow for observation of intermittent degrees of delocalization throughout the annulenic core. A consistent relationship between the magnitude of the NICS values and the degree of benzannelation is also observed.

Full text of DOI:10.1021/jo020463i

Dia tr op icity of 3,4,7,8,9,10,13,14-Octa d eh yd r o[14]a n n u len es: A
Com bin ed Exp er im en ta l a n d Th eor etica l In vestiga tion
Andrew J . Boydston,† Michael M. Haley,*,† Richard Vaughan Williams,*,‡ and
J ohn R. Armantrout‡
Department of Chemistry, University of Oregon, Eugene, Oregon 97403-1253, and
Department of Chemistry, University of Idaho, P.O. Box 442343, Moscow, Idaho 83844-2343
haley@oregon.uoregon.edu; williams@neon.chem.uidaho.edu
Received J uly 11, 2002
The synthesis and study of a series of octadehydro[14]annulenes is described. The aromaticity of
these annulenes was investigated through examination of experimental data from arene-fused
systems as well as calculated nucleus-independent chemical shifts (NICS) and bond lengths. Benzene
ring fusion to the parent system results in a stepwise loss in aromaticity as the number of fused
rings is increased from one to two to three. This decrease in annulenic ring current is manifested
in the alkene proton chemical shifts (0-2 benzenes) as well as the NICS (0-3 benzenes). Comparison
of isomeric thiophene-fused annulenes shows further evidence of ring current competition as these
allow for observation of intermittent degrees of delocalization throughout the annulenic core. A
consistent relationship between the magnitude of the NICS values and the degree of benzannelation
is also observed.
In tr od u ction
mixed results.5 Vollhardt,6 Sundholm,7 and Elguero8 have
each used NICS to study DBAs, though not without some
disparity of their results. In considering all of these
studies, two facts become evident: (1) conclusions based
solely on experimental observations can sometimes be
overly optimistic, and (2) computational approaches are
complicated by varying levels of theory, asymmetry of the
study molecule, contributions from anisotropic regions of
the macrocycle, and the size of the conjugated backbone.
Bunz’s group recently reported interesting comparative
aromaticity studies on arene-fused annulenes.9 An im-
portant assumption in their argument was the ability of
the 3,4,7,8,9,10,13,14-octadehydro[14]annulene skeleton
(1) to undergo ring current competition. This sparked our
initial interest in trying to understand the extent to
which 1 could be considered aromatic.10 Although it is
generally accepted that certain [14]annulenes11 and [18]-
An intensely investigated and debated area of dehy-
droannulene (DA) and dehydrobenzoannulene (DBA)
chemistry involves the study of induced ring currents in
these macrocycles.1 With increased benzannelation and
higher degrees of unsaturation (i.e., triple versus double
bonds), many systems become suspect as to whether they
can accurately be considered aromatic or antiaromatic.
This issue has been addressed on two fronts. Classically,
experimental observations, based mainly on proton NMR
data,2 provide strong evidence for the existence of ring
currents in most DAs and DBAs. More recently, theoreti-
cal work, specifically nucleus-independent chemical shifts
(NICS),3 has improved our ability to understand this
fundamental yet elusive property of these macrocycles.
We have shown qualitatively through experiment that
DBAs possess an induced ring current despite their large
size, extensive benzannelation, and high degree of un-
saturation.4 Unfortunately, as shown in the preceding
paper in this issue, efforts to quantify the ring current
of DAs and DBAs fused to dimethyldihydropyrene (DDP),
Mitchell’s elegant NMR probe for aromaticity, afforded
(4) (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.
(5) 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, 8798-8811.
† University of Oregon.
‡ University of Idaho.
(6) Matzger, A. J .; Vollhardt, K. P. C. Tetrahedron Lett. 1998, 39,
6791-6794.
(1) (a) Balaban, A. T.; Banciu, M.; Ciorba, V. Annulenes, Benzo-,
Hetero-, Homo- Derivatives and their Valence Isomers; CRC Press: Boca
Raton, FL, 1987; Vols. 1-3. (b) Garratt, P. J . Aromaticity; Wiley: New
York, 1986. (c) Minkin, V. I.; Glukhovtsev, M. N.; Simkin, B. Ya.
Aromaticity and Antiaromaticity; Wiley: New York, 1994. (d) Chem.
Rev. 2001, 101 (5) (“Aromaticity” special issue).
(2) (a) Mitchell, R. H. Chem. Rev. 2001, 101, 1301-1315. (b)
Mitchell, R. H.; Williams, R. V.; Dingle, T. W. J . Am. Chem. Soc. 1982,
104, 2560-2572. (c) Mitchell, R. H.; Williams, R. V.; Mahadevan, R.;
Lai, Y.-H.; Dingle, T. W. J . Am. Chem. Soc. 1982, 104, 2571-2578.
(3) Schleyer, P. von R.; Maerker, C.; Dransfeld, A.; J iao, H.;
Hommes, N. J . R. van E. J . Am. Chem. Soc. 1996, 118, 6317-6318.
(7) J use´lius, J .; Sundholm, D. Phys. Chem. Chem. Phys. 2001, 3,
2433-2437.
(8) Alkorta, I.; Rozas, I.; Elguero, J . Tetrahedron 2001, 57, 6043-
6049.
(9) 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.
(10) Boydston, A. J .; Haley, M. M. Org. Lett. 2001, 3, 3599-3601.
(11) Gu¨nther, H.; Gu¨nther, M. E.; Mondeshka, D.; Schmickler, H.;
Sondheimer, F.; Darby, N.; Cresp, T. M. Chem. Ber. 1979, 112, 71-
83.
10.1021/jo020463i CCC: $22.00 © 2002 American Chemical Society
Published on Web 11/19/2002
8812
J . Org. Chem. 2002, 67, 8812-8819

Diatropicity of Octadehydro[14]annulenes
SCHEME 1 a
a
Reagents and conditions: (a) K2CO3, MeOH, THF; (b) (Z)-1,2-
dichloroethene, Pd(PPh3)4, CuI, PrNH2, THF; (c) Bu4NF, THF,
MeOH; (d) Cu(OAc)2, MeCN, 100 °C. Th ) thexyl ) 1,1,2-
trimethylpropyl.
SCHEME 2 a
a
Reagents and conditions: (a) K2CO3(aq), MeOH, THF; (b) (Z)-
(4-chloro-3-buten-1-ynyl)trimethylsilane, Pd(PPh3)4, CuI, PrNH2,
THF; (c) Cu(OAc)2, MeCN, 100 °C.
yield. Deprotection with Bu4NF and cyclization under
Vo¨gtle’s conditions15 produced macrocycle 1, which was
stable only in dilute solutions.
Symmetric monobenzannelated annulene 216 was pre-
pared from 1,2-bis(trimethylsilylethynyl)benzene17 (11)
and (Z)-(4-chloro-3-buten-1-ynyl)trimethylsilane18 (Scheme
2). Deprotection of the aryldiyne unit using methanolic
K2CO3, followed by cross-coupling to the chloroalkene,
furnished terminally protected polyyne 12 in 94% yield
for the two steps. Stepwise deprotection and cyclization
provided the desired macrocycle, which polymerized to
form an insoluble black film upon concentration.
The synthesis of asymmetric monobenzannelated 3
(Scheme 3) made use of monoprotected phenyldiyne
13,4b,19 which was cross-coupled to (Z)-(4-chloro-3-buten-
1-ynyl)trimethylsilane to provide 14 in 87% yield. Depro-
tection and repeated cross-coupling gave polyyne 15 in
83% yield. Protiodesilylation with Bu4NF and MeOH
followed by cyclization furnished unstable benzocyclyne
3.
The synthesis of 4 is shown in Scheme 4. Starting from
known iodoarene 16,4b,19 an in situ deprotection/alkynyl-
ation procedure4b,19 was employed to give polyyne 17 in
75% yield. Deprotection and cyclization as before fur-
nished 4, which was stable only in dilute solutions.
With dibenzoannulene 520 and tribenzoannulene 621
already known, we proceeded to compare proton chemical
shifts to determine whether a stepwise decrease in
aromaticity resulted as the number of fused rings in-
F IGURE 1. Octadehydro[14]annulene 1 and arene-fused
analogues 2-8. For comparison purposes, the top left sp2
carbon is position 1 and the remaining carbons of the 14-
membered ring are numbered in a clockwise manner.
annulenes12 are in fact aromatic, increased unsaturation
and ring strain are known to reduce delocalization;1 thus,
this gives rise to skepticism about the aromaticity of 1.
With the specific criteria for aromaticity, and even a
universal definition, still being an issue of debate,13 we
felt it was pragmatic to probe a specific system using both
experimental and theoretical tools. To strengthen our
arguments for the existence of aromaticity in octadehydro-
[14]annulenes, we report herein a comprehensive study
of the ring current in 1 and arene-fused analogues 2-8
(Figure 1). This investigation involves (1) stepwise reduc-
tion in the macrocyclic ring current as a result of
successive benzannelation, (2) examination of the sensi-
tivity of the annulenic core to changes in the degree of
conjugation allowed by regioisomeric thieno fusion, and
(3) theoretical evidence of aromaticity and a relative
quantification using NICS.
Resu lts a n d Discu ssion
Decr ea se of Ar om a ticity by Ben za n n ela tion . Al-
though a few derivatives have been reported, surprisingly
the parent octadehydro[14]annulene (1) was an unknown
molecule. The straightforward synthesis of this macro-
cycle is described in Scheme 1. Selective deprotection of
enediyne 914 followed by Pd-catalyzed cross-coupling with
(Z)-1,2-dichloroethene furnished R,ω-polyyne 10 in 61%
(15) Bersheid, R.; Vo¨gtle, F. Synthesis 1992, 58-62. (b) Haley, M.
M.; Bell, M. L.; Brand, S. C.; Kimball, D. B.; Wan, W. B. Tetrahedron
Lett. 1997, 38, 7483-7486.
(16) Boydston, A. J .; Bondarenko, L.; Dix, I.; Weakley, T. J . R.; Hopf,
H.; Haley, M. M. Angew. Chem., Int. Ed. 2001, 40, 2986-2989.
(17) Takahashi, S.; Kuroyama, Y.; Sonogashira, K.; Hagihara, N.
Synthesis 1980, 627-630.
(18) J ohn, J . A.; Tour, J . M. Tetrahedron 1997, 53, 15515-15534.
(19) Haley, M. M.; Bell, M. L.; English, J . J .; J ohnson, C. A.;
Weakley, T. J . R. J . Am. Chem. Soc. 1997, 119, 2956-2957.
(20) Blanchette, H. S.; Brand, S. C.; Naruse, H.; Weakley, T. J . R.;
Haley, M. M. Tetrahedron 2000, 56, 9581-9588.
(21) Baldwin, K. P.; Matzger, A. J .; Scheiman, D. A.; Tessier, C. A.;
Vollhardt, K. P. C.; Youngs, W. J . Synlett 1995, 1215-1218.
(12) Nishinaga, T.; Kawamura, T.; Komatsu, K. J . Org. Chem. 1997,
62, 5354-5362.
(13) Gomes, J . A. N. F.; Mallion, R. B. Chem. Rev. 2001, 101, 1349-
1383 and references therein.
(14) Bharucha, K. N.; Marsh, R. M.; Minto, R. E.; Bergman, R. G.
J . Am. Chem. Soc. 1992, 114, 3120-3121.
J . Org. Chem, Vol. 67, No. 25, 2002 8813

Boydston et al.
SCHEME 3 a
TABLE 2. Alk en e P r oton Ch em ica l Sh ifts (p p m ) of
Cyclized Com p ou n d sa
proton
1
2
3
4
5
H1
H2
H11
H12
7.77
7.77
7.39
7.92
7.03
7.16
6.74
7.24
6.72
6.72
6.73
7.41
6.37
7.01
a
In CD2Cl2.
TABLE 3. Ch em ica l Sh ift Differ en ce (p p m ) of Alk en e
P r oton s u p on Su ccessive Ben za n n ela tion
proton
1 f 3
1 f 2
3 f 4
3 f 5
2 f 4
H1
H2
H11
H12
-0.74
-0.61
-0.65
-0.68
-0.31
-0.44
-0.66
-0.51
-0.37
-0.23
-0.36
-0.40
half.2a,22 It is worth noting that the specific site of ring
fusion has little effect between regioisomers (compare 2
to 3), with the exception of an alkene proton γ to a
bridging carbon. For this case, ca. 0.15 ppm must be
added to the ∆δ value (e.g., H12 in 1 f 2 vs 1 f 3). This
adjustment is attributed to the steric deshielding effect
of the nearby arene proton.
a
Reagents and conditions: (a) (Z)-(4-chloro-3-buten-1-ynyl)tri-
methylsilane, Pd(PPh3)4, CuI, PrNH2, THF; (b) NaH, MeOH, THF;
(c) Bu4NF, THF, MeOH; (d) Cu(OAc)2‚H2O, MeCN, 100 °C.
SCHEME 4 a
In ter m itten t Degr ees of Deloca liza tion . Encour-
aged by the results presented above, we became curious
about the effects of allowing intermittent degrees of
delocalization. This could be achieved by fusing a
thiophene ring to the annulene backbone in two different
regioisomeric fashions. This was inspired by Sond-
heimer’s observation that fusing an annulene moiety
across the 2-3 bond of naphthalene (18) resulted in less
aromatic character in the [14]annulene moiety than when
fusion was done across the 1-2 bond (19).23 The change
a
Reagents and conditions: (a) 9, K2CO3, MeOH, PdCl2(PPh3)2,
CuI, Et3N; (b) Bu4NF, THF, MeOH; (c) Cu(OAc)2, MeCN, 100 °C.
TABLE 1. Alk en e P r oton Ch em ica l Sh ifts (p p m ) of
P r ecyclized Com p ou n d sa
protonb
10
12
15
17
pre-5c
21
23
H1
H11
H12
6.05
5.90
6.07
6.11
5.91
6.11
6.11
5.94
6.17
5.95
6.15
5.91
6.07
5.90
6.11
a
b
In CD2Cl2. Proton numbering in the precyclized compounds
is analogous to that shown in Figure 1, minus the C8-C9
diacetylene single bond. c Reference 20.
in ring current was manifested in the chemical shifts of
the alkene and methyl protons about the macrocycle, and
is attributable to less double bond character in the 2-3
bond than in the 1-2 bond in naphthalene. Similar to
the naphthalene case, thiophene also exhibits bond
alternation, with the 3-4 bond in a thiophene ring known
to possess less double bond character than the 2-3
bond.24 The effects of such “bond localization” have been
observed in the properties of other thieno-fused dehy-
droannulenes,25 and should be rather pronounced for 7
and 8.
creased. First it was necessary to establish whether the
simple inclusion of a benzene ring into the conjugated
backbone had an effect on the overall deshielding of the
alkene protons. Table 1 shows the chemical shifts of
similar protons in each system. It is clear that prior to
cyclization the alkene protons give little acknowledgment
of the aryl moiety.
Upon cyclization, however, there is a distinct loss in
aromaticity of the 14-membered macrocycle when the
number of benzene rings is increased from zero to one,
as illustrated by the upfield shift of the alkene protons
(Table 2). In this case, the change in resonance (∆δ) of
the alkene protons is, on average, an upfield shift of 0.67
ppm (Table 3). Fusion of a second benzene ring results
in an additional average ∆δ of 0.38 ppm. The mean ∆δ
values are consistent with the notion that benzannelation
reduces aromaticity in an annulene circuit by about
(22) Mitchell, R. H. Isr. J . Chem. 1980, 20, 294-299.
(23) (a) Walsgrove, T. C.; Sondheimer, F. Tetrahedron Lett. 1978,
2719-2722.
(24) Fringuelli, F.; Marino, G.; Taticchi, A. J . Chem. Soc., Perkin
Trans. 2 1974, 332-337.
(25) (a) J ones, R. R.; Brown, J . M.; Sondheimer, F. Tetrahedron Lett.
1975, 4183-4186. (b) Sarkar, A.; Haley, M. M. Chem. Commun. 2000,
1733-1734.
8814 J . Org. Chem., Vol. 67, No. 25, 2002

Diatropicity of Octadehydro[14]annulenes
SCHEME 5 a
ppm). The electronic absorption spectra also support the
more aromatic character of 8. In 7 the λmax is 304 nm,
whereas in 8 the λmax exhibits a small but distinguishable
bathochromic shift to 318 nm.
We next compared the extent of delocalization in our
parent, fully conjugated system to that in the 1,2-dihydro
analogue 24 reported by Schreiber’s group.28 By breaking
the conjugation, we can compare two systems with nearly
identical degrees of unsaturation, but with one being
nonaromatic and the other having a classically aromatic
structure. The alkene protons of 24 have chemical shifts
of 6.19 and 5.79 ppm. In comparison with those of 1 (7.92
and 7.39 ppm), it is clear that a diatropic ring current is
present when the system is fully conjugated. Such a
difference in chemical shifts cannot be ascribed to the
anisotropy of the 1-2 double bond in 1.
a
Reagents and conditions: (a) 1-(triisopropylsilyl)-6-(trimeth-
ylsilyl)-3-hexen-1,5-diyne, K2CO3, MeOH, Pd(PPh3)4, CuI, i-Pr2NEt,
THF, 100 °C; (b) Bu4NF, THF, MeOH; (c) Cu(OAc)2‚H2O, MeCN,
100 °C; (d) K2CO3, MeOH, THF; (e) (Z)-(4-chloro-3-buten-1-
ynyl)trimethylsilane, Pd(PPh3)4, CuI, PrNH2, THF; (f) K2CO3,
MeOH, Cu(OAc)2‚H2O, MeCN, 100 °C.
Com p u ta tion a l Stu d ies. To provide further insight
into the effects of benzannelation upon the aromaticity
of the octadehydro[14]annulene (ODA) nucleus, we un-
dertook a computational investigation similar to that
used in the accompanying paper.5 Geometries were
optimized using the B3LYP/6-31G* method as imple-
mented in J aguar 4.029 and were confirmed to be minima
through their calculated energy second derivatives.
Nucleus-independent chemical shifts3,30 were calculated
using the Hartree-Fock (HF) gauge-invariant atomic
orbital (GIAO) method on the B3LYP/6-31G*-optimized
geometries (GIAO-HF/6-31G*//B3LYP/6-31G*) with the
Gaussian 98 suite of programs.31
Comparison of calculated and experimental bond lengths
for compounds 5 and 6 (Supporting Information Table
S1) and of calculated and experimental NMR chemical
shifts for compounds 1-8 and 24 (1H, Supporting Infor-
mation Tables S2 and S3; 13C, Supporting Information
Tables S4 and S5) reveals a reassuringly close agreement
between theory and experiment, verifying the appropri-
ateness of the level of theory used for this study.
Schleyer and co-workers demonstrated that NICS is
an effective tool for the detection of aromaticity, equating
negative NICS values with the existence of aromaticity
in the ring system under investigation.3,32 Recently,
through the use of NICS, we showed not only that it
The synthesis of thienoannulenes 7 and 8 is shown in
Scheme 5. In situ deprotection/alkynylation involving 3,4-
diiodothiophene (20) and 1-(triisopropylsilyl)-6-(trimeth-
ylsilyl)-3-hexen-1,5-diyne26 gave the requisite synthon 21
in 67% yield. Varying the solvent, reaction time, reaction
temperature, and base only resulted in much lower
yields. The combination of Hu¨nig’s base and THF at 100
°C gave the only yield above 25%. Deprotection and
cyclization gave the symmetric annulene, which polym-
erized even in dilute solutions at -20 °C. The same
strategy was applied to the synthesis of asymmetric 8,
but with unsatisfying results. Cross-coupling under the
same conditions that produced 21 only resulted in modest
amounts of monocoupled product. The site of alkynylation
was not determined, nor was it of interest. Instead,
known diethynylthiophene 2227 was prepared in nearly
quantitative yield utilizing Hu¨nig’s base and THF at 100
°C. Deprotection and cross-coupling furnished 23 in 55%
yield. Although no deprotected diethynylthiophene was
found, attempts to increase the yield were unsuccessful.
Use of an in situ deprotection/cyclization procedure,
modified from Vo¨gtle’s conditions,15 gave cleanly the
desired macrocycle, but with the usual instability upon
concentration.
Gratifyingly, the thieno[14]annulenes provided the
desired results. Proton NMR spectroscopy confirmed that
the thiophene ring in the symmetrical system retained
more of its ring current upon cyclization than did the
thiophene ring in the asymmetric macrocycle. This is
evident from the arene proton chemical shifts of each
thiophene nucleus in the two macrocycles (8.01 ppm in
7, 7.81 and 7.69 ppm in 8). In 8, the increased double
bond character at the site of fusion results in an obvious
increase in delocalization in the [14]annulenic circuit in
comparison with that in 7. Each of the alkene protons of
8 (7.60, 7.58, 7.02, and 6.97 ppm) appear further down-
field than those of the less aromatic 7 (6.93 and 6.32
(28) Elbaum, D.; Toan, N.; J orgensen, W.; Schreiber S. Tetrahedron
1994, 50, 1503-1518.
(29) J aguar 4.0, Schro¨dinger, Inc., Portland, OR, 1991-2000.
(30) Patchkovskii, S., Thiel, W. J . Mol. Model 2000, 6, 67-75.
(31) 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.; 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.; Gonzalez, C.; Challacombe, M.; Gill, P.
M. W.; J ohnson, B. G.; Chen, W.; Wong, M. W.; Andres, J . L.; Head-
Gordon, M.; Replogle, E. S.; Pople, J . A., Gaussian, Inc., Pittsburgh,
PA, 1998.
(26) Lu, Y.-F.; Harwig, C. W.; Fallis, A. G. J . Org. Chem. 1993, 58,
4202-4204.
(27) Sugihara, Y.; Miyatake, R.; Tagi, T. Chem. Lett. 1993, 933-936.
(32) Also see ref 30 and references therein.
J . Org. Chem, Vol. 67, No. 25, 2002 8815

Boydston et al.
1
δ(n ) ) experimental H chemical shift of H11 or H12
on ODA n ,
1
δ(1) ) experimental H chemical shift of H11 or H12
on 1 (7.39 and 7.92 ppm, respectively),
RANICS ) NICS relative aromaticity of ODA n (com-
pared to 1),
NICS (24) ) NICS value at point A(0) for 24 (0.88),
NICS(n ) ) NICS value at NICS point A(0) for ODA n ,
and
NICS(1) ) NICS value at NICS point A(0) for 1
(-8.12).
In the preceding paper,5 we determined that the ODA
nucleus is indeed aromatic, albeit weakly so. Additional
support for this conclusion is provided by comparing the
properties of the parent ODA (1) with Sondheimer’s
“dihydro” derivative 25. Hexadehydro[14]annulene (25)
is indisputably diatropic as affirmed by the substantial
difference in the observed 1H chemical shifts of the
inner proton (H7, δ -4.96 ppm) and the outer protons
(H1,2,5,6,8,11,12, δ 9.47-8.08 ppm).34 The protons on 1
(δ 7.77-7.92 ppm) resonate at only slightly higher field
than the outer protons of 25, a clear indication of a
diatropic ring current in 1. The NICS values at point A(0)
for 1 and 25 (Figure 2) are also of very similar magnitude,
-8.12 and -8.72, respectively, again indicating that the
more unsaturated 1 is only slightly less aromatic than
25.
F IGURE 2. Numbering scheme and location of the NICS
points for 6-8 and 25. NICS points: A, center of C1-14; B,
center of C2-8; C, center of C14 and C1-7; D, center of C1
and C14-8. The corresponding numbering scheme and loca-
tion of the NICS points for 1-5 and 24 is accomplished by
deleting the appropriate fused arenes.
is possible to detect aromaticity, but also that the
magnitude of the NICS correlates with the experi-
mental degree of aromaticity in
a wide range of
dimethyldihydropyrenes.33 We calculated NICS at four
locations in the ODA ring (points A-D in Figure 2) and
also at 0.25 Å increments along the normal to the ODA
ring plane from each of these points (Table 4, Supporting
Information Table S6).
It is well-known that benzannelation of an annulene
causes bond localization with a concomitant reduction in
the diatropicity of the annulene.35 We thus expected
benzene fusion to ODA to result in a reduction in
It is immediately apparent from the inflated NICS
values associated with points B-D (especially for com-
pound 24, which is not aromatic due to the interrupted
conjugation) that local anisotropies are adversely affect-
ing the NICS at these points. The NICS at point A (A(0))
and along the normal emanating from this point (A(0.25)-
A(2.00)) show almost identical ordering of aromaticity for
the ODA nucleus of compounds 1-8 and the related
species 24 and 25 (Table 4). The only difference in
progressing from A(0) to A(2.00) is a reversal in the order
of the essentially indistinguishable aromaticities of 4 and
5 in going from points A(0)-A(0.50) to points A(0.75)-
A(2.00). We therefore, as in the preceding paper,5 chose
to define the NICS relative aromaticity (RANICS) of the
octadehydro[14]annulene (ODA) nucleus in terms of the
NICS determined at A(0). For both the experimental
relative aromaticity (RAexptl) and the RANICS we used the
nonaromatic model 24 and the fully aromatic parent (1)
as reference compounds (eqs 1 and 2).
1
diatropicity of the ODA nucleus. The H NMR chemical
shifts observed for 1-5 indicate an approximate 50%
reduction in aromaticity of the ODA nucleus for each
benzene fusion (vide supra). Our NICS results, princi-
pally focusing on points A (Table 4), are in complete
agreement with this experimental ordering of aromaticity
and, in addition, demonstrate that the degree of aroma-
ticity of the ODA nucleus in 6 is about 50% of that in 5.
We previously found that RAs furnish a reliable ordering
of aromaticity, but that their absolute magnitude is not
of particular significance.5,33 Examination of both the
experimental and calculated RAs in Table 5 shows that
the order of aromaticity of the ODA nuclei in 1-6 is
1 > 2 ≈ 3 > 4 ≈ 5 > 6
As we observed previously,5,33 calculated RAs indicate a
greater reduction in diatropicity of the annulene upon
annelation than do the experimental RAs.
Vollhardt and Matzger reported the NICS (GIAO-
B3LYP/6-31G*//B3LYP/6-31G*) for 6 at point A(0) to be
-1.79 (compare with the corresponding NICS, -0.04, in
Table 4).6 The discrepancy between these NICS values
is accounted for by the fact that Vollhardt and Matzger
used the GIAO-B3LYP/6-31G* method while in this study
we used the GIAO-HF/6-31G* method to calculate NICS.
We concur with their conclusion that 6 is very weakly
diatropic (RANICS ) 10.2%, Table 5).
δ(24) - δ(n )
δ(24) - δ(1)
RAexptl
)
× 100
(1)
(2)
NICS(24) - NICS(n )
× 100
NICS(24) - NICS(1)
RANICS
)
RAexptl ) experimental relative aromaticity of ODA n
(compared to 1),
1
δ(24) ) experimental H chemical shift of H11 or H12
on 24 (5.6 and 6.0 ppm, respectively),
(33) Williams, R. V.; Armantrout, J . R.; Twamley, B.; Mitchell, R.
H.; Ward, T. R.; Bandyopadhyay, S. J . Am. Chem. Soc. 2002, 124,
13495-13505.
(34) Mayer, J .; Sondheimer, F. J . Am. Chem. Soc. 1966, 88, 602-
603.
(35) See Vol. II, Chapter 7, in ref 1a.
8816 J . Org. Chem., Vol. 67, No. 25, 2002

Diatropicity of Octadehydro[14]annulenes
TABLE 4. NICS Va lu es for Com p ou n d s 1-8, 24, a n d 25a
1
2
3
4
5
6
7
8
24
25
A(0)
-8.12
-8.05
-7.85
-7.53
-7.10
-6.59
-6.04
-5.46
-4.89
-3.64
-3.61
-3.52
-3.38
-3.20
-2.99
-2.77
-2.55
-2.33
-3.60
-3.57
-3.48
-3.33
-3.15
-2.93
-2.70
-2.47
-2.24
-1.28
-1.27
-1.23
-1.18
-1.12
-1.08
-1.04
-1.00
-0.96
-1.30
-1.29
-1.24
-1.18
-1.12
-1.05
-0.99
-0.94
-0.88
-0.04
-0.04
-0.02
-0.02
-0.02
-0.05
-0.10
-0.15
-0.20
-1.10
-1.09
-1.05
-1.01
-0.97
-0.92
-0.88
-0.84
-0.80
-6.16
-6.10
-5.94
-5.69
-5.35
-4.96
-4.55
-4.12
-3.71
0.88
0.88
0.87
0.85
0.81
0.75
0.67
0.59
0.51
-8.72
-8.62
-8.34
-7.96
-7.51
-7.02
-6.48
-5.92
-5.35
A(0.25)
A(0.50)
A(0.75)
A(1.00)
A(1.25)
A(1.50)
A(1.75)
A(2.00)
a
For the complete table including NICS points B-D, please see Table S6 in the Supporting Information.
TABLE 5. Rela tive Ar om a ticity (%) of th e ODA Nu cleu s
to be accurately studied using the dimethyldihydropyrene
probe.5 Although the magnitude of ring current present
in these ODAs is below the advisory limits for use of a
DDP hybrid to quantify the aromaticity, the combination
of sensitive alkene proton chemical shifts with consistent
calculated data has allowed for a strong understanding
of the relative amounts of induced ring current in these
systems. Mean ∆δ values upon successive benzannelation
provide insight into the relative amount of ring current
present after fusion. NICS calculations provide data in
excellent agreement with the experimentally observed
trends.
of 2-8
a
RAexptl(H11)
RAexptl(H12)
RANICS
2
3
4
5
6
7
8
63.1
63.1
43.0
73.4
64.6
52.6
50.2
49.8
24.0
24.2
10.2
22.0
78.2
40.2
79.3
48.4
88.0
a
Relative aromaticity (%) calculated using NICS point A(0).
Consistent with the reductions in aromaticity upon
benzannelation of 1, reported above, this annelation also
causes the expected bond localization in compounds 2-6
(Table S1). The calculated (and experimental) “single”
bond lengths (2-3, 4-5, 6-7, 8-9, 10-11, 12-13, and
14-1) are longer, while the “triple” bond lengths (3-4,
7-8, 9-10, and 13-14) are shorter than those in 1. The
“double” bonds of 2-5, which are not benzannelated,
show a similar shortening, while the “double” bonds at
the sites of annelation are elongated compared with those
in 1. In general for 2-6, the more benzene rings fused
to the ODA nucleus the greater the observed lengthening/
shortening of the ODA bonds.
Exp er im en ta l Section
Ma ter ia ls a n d Meth od s. 1H and 13C NMR spectra were
recorded on a 300 MHz (1H, 299.94 MHz; 13C, 75.43 MHz)
spectrometer. Chemical shifts (δ) are expressed in parts per
million downfield from tetramethylsilane using the residual
solvent as an internal standard (CDCl3, 1H 7.26, 13C 77.00;
CD2Cl2, 1H 5.32, 13C 54.00). Coupling constants are expressed
in hertz. Et3N and PrNH2 were 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 manufacturers. Column chromatography
was performed on reagent grade silica gel (230-400 mesh).
Preparative radial thin-layer chromatography was performed
using silica gel (60 PF254) plates (1-4 mm). Precoated silica
gel plates (200 × 50 × 0.25 mm) were used for analytical thin-
layer chromatography. Reactions were carried out in an inert
atmosphere (dry N2) when necessary.
As already noted from the experimental 1H NMR
chemical shifts, thiophene fusion to the ODA attenuates
the diatropicity of this nucleus, with the ODA of 7 being
significantly less aromatic than that of 8. Our calculated
data similarly demonstrate for the ODA nucleus of 8 a
relatively high degree of aromaticity (reasonably large
negative NICS, deshielded peripheral protons, and sig-
nificant bond equalization) while 7 has properties more
typical of dibenzannelated ODAs 4 and 5 (Tables 4 and
S2-S5). The more efficient delocalization in the ODA
nucleus of 8 than 7 is due to the increased double bond
character of the thiophene 2-3 bond over the 3-4 bond,
or alternatively, the difference in character between 7
and 8 can also be explained by viewing 7 as a zero-
bridged dehydrothia[17]annulene in which 18 π electrons
are delocalized over the whole periphery while 8 is a
thieno-annelated ODA. Following the usual trend, the
larger annulene 7 is less aromatic than the effectively
smaller annulene 8.1
r,ω-P olyyn e 10. Enediyne 914 (347 mg, 1.19 mmol) was
dissolved in MeOH/THF (50 mL, 1:1 v/v), and K2CO3 (332 mg,
2.40 mmol) was added. The mixture was stirred for 2-3 h and
monitored by TLC. Upon completion, the reaction was diluted
with Et2O, washed successively with saturated NH4Cl solution,
brine, and H2O, dried (MgSO4), and filtered. Concentration of
the product gave the monoprotected enediyne in sufficiently
pure form and nearly quantitative yield.
The above enediyne was dissolved in THF (30 mL) and
PrNH2 (0.20 mL, 2.40 mmol) and the mixture degassed by N2
bubbling for 30 min. To this were added (Z)-1,2-dichloroethene
(47 mg, 0.48 mmol), Pd(PPh3)4 (33 mg, 0.03 mmol), and CuI
(91 mg, 0.48 mmol). After being stirred overnight, the reaction
mixture was filtered through a thin pad of silica, eluting with
Et2O, and then concentrated. Purification by column chroma-
tography on silica (0.1% Et3N in hexanes) provided 10 (134
mg, 61%) as an orange oil: 1H NMR (CD2Cl2) δ 6.07 (d, J )
10.7, 2H), 6.05 (s, 2H), 5.90 (d, J ) 10.7, 2H), 1.70 (septet, J
) 7.2, 2H), 0.94 (s, 12H), 0.93 (d, J ) 7.2, 12H), 0.20 (s, 12H);
13C NMR (CD2Cl2) δ 120.97, 120.57, 120.01, 104.68, 103.43,
95.72, 94.89, 35.13, 23.93, 20.99, 19.02, -2.34; IR (neat) ν 3042,
3026, 1673, 1584 cm-1; UV-vis (CH2Cl2) λmax (ꢀ) 244 (10650),
285 (11750), 296 (13100), 382 (13200), 354 (19350) nm; MS
(ES+) m/z (rel intens) 478.3 (100, M+ + H2O).
Con clu sion s
The synthesis and comparative aromaticity study of a
family of octadehydro[14]annulenes has been accom-
plished. Experimentally, proton NMR analysis allows for
a qualitative comparison of aromaticity which has dis-
closed evidence for a weak induced ring current too subtle
3,4,7,8,9,10,13,14-Octa d eh yd r o[14]a n n u len e (1). R,ω-
Polyyne 10 (40 mg, 0.09 mmol) was dissolved in THF (25 mL),
J . Org. Chem, Vol. 67, No. 25, 2002 8817

Boydston et al.
and three drops of MeOH was added. To this solution was
added Bu4NF (1.0 M in THF, 0.22 mL) in one portion, and the
reaction was stirred for 3 h. Upon completion, the mixture was
diluted with Et2O, washed successively with saturated NH4-
Cl solution, brine, and H2O, dried (MgSO4), and filtered.
Concentration of the product gave the deprotected tetrayne
in sufficiently pure form and nearly quantitative yield.
14 (112 mg, 87%) as a light orange oil: 1H NMR (CD2Cl2) δ
7.51-7.48 (m, 2H), 7.32-7.29 (m, 2H), 6.06 (d, J ) 10.9, 1H),
5.91 (d, J ) 10.9, 1H), 1.15 (s, 21H), 0.23 (s, 9H); 13C NMR
(CD2Cl2) δ 132.97, 132.86, 128.97, 128.68, 126.41, 126.25,
121.12, 120.32, 105.58, 104.16, 102.69, 96.75, 96.03, 91.22,
19.02, 12.37, 0.13; IR (neat) ν 3061, 3027, 2157, 2144 cm-1
;
UV-vis (CH2Cl2) λmax (ꢀ) 255 (16150), 260 (16050), 269 (21850),
318 (22100), 341 (20250) nm; MS (APCI) m/z (rel intens) 405.2
(8, M+), 145.1 (100).
r,ω-P olyyn e 15. Enetriyne 14 (112 mg, 0.28 mmol) was
dissolved in MeOH/THF (40 mL, 1:1 v/v), and NaH (33 mg,
1.38 mmol) was added. After being stirred for 30 min, the
solution was diluted with Et2O, washed successively with
saturated NH4Cl solution, brine, and H2O, dried (MgSO4), and
filtered. Concentration of the product gave the free enetriyne
in sufficiently pure form and nearly quantitative yield.
The above tetrayne was dissolved in MeCN (200 mL), and
Cu(OAc)2 (359 mg, 1.80 mmol) was added. The blue-green
slurry was stirred at reflux for 24 h. After cooling, the reaction
mixture was diluted with Et2O, washed with H2O, dried
(MgSO4), filtered, and concentrated. The annulene polymerized
rapidly upon concentration to give a thick purple oil (dilute
solutions of 1 can be stored at -20 °C): 1H NMR (CD2Cl2) δ
7.92 (d, J ) 10.2, 2H), 7.77 (br s, 2H), 7.39 (d, J ) 10.2, 2H);
13C NMR (CD2Cl2) δ 125.37, 117.88, 117.37, 100.80, 100.34,
92.21, 86.88; IR (CH2Cl2) ν 3155, 3052, 2253, 1468, 1380 cm-1
;
The deprotected material was dissolved in THF (40 mL) and
PrNH2 (0.05 mL, 0.56 mmol) and the mixture degassed by N2
bubbling for 40 min. To this were added (Z)-(4-chloro-3-buten-
1-ynyl)trimethylsilane (89 mg, 0.56 mmol), Pd(PPh3)4 (16 mg,
0.01 mmol), and CuI (53 mg, 0.28 mmol). After being stirred
overnight, the reaction mixture was filtered through a thin
pad of silica, eluting with Et2O, and then concentrated.
Purification by column chromatography (0.1% Et3N, 10% CH2-
Cl2 in hexanes) provided 15 (106 mg, 83%) as a light orange
oil: 1H NMR (CD2Cl2) δ 7.51-7.48 (m, 2H), 7.31-7.28 (m, 2H),
6.11 (d, J ) 11.0, 1H), 6.10 (s, 2H), 5.91 (d, J ) 11.0, 1H), 1.15
(s, 21H), 0.15 (s, 9H); 13C NMR (CD2Cl2) δ 133.26, 132.90,
128.96, 128.69, 126.38, 126.21, 120.77, 120.67, 120.57, 119.79,
105.56, 104.74, 102.53, 97.26, 96.07, 95.33, 95.25, 91.30, 19.01,
UV-vis (CH2Cl2, qualitative) λmax 228, 296, 339, 347 nm; MS
(ES+) m/z (rel intens) 175.1 (14, M+ + H), 126.9 (40, C10H6).
r,ω-P olyyn e 12. 1,2-Bis(trimethylsilylethynyl)benzene17
(125 mg, 0.46 mmol) was dissolved in MeOH/THF (50 mL, 1:1
v/v), and K2CO3 (319 mg, 2.31 mmol) was added. The mixture
was stirred for 2-3 h and monitored by TLC. Upon completion,
the reaction was diluted with Et2O, washed successively with
saturated NH4Cl solution, brine, and H2O, dried (MgSO4), and
filtered. Concentration of the product gave the free diethynyl-
benzene in sufficiently pure form and nearly quantitative yield.
The resulting 1,2-diethynylbenzene was dissolved in THF
(25 mL) and PrNH2 (0.19 mL, 2.31 mmol) and the mixture
degassed by N2 bubbling for 30 min. To this were added (Z)-
(4-chloro-3-buten-1-ynyl)trimethylsilane18 (154 mg, 0.97 mmol),
Pd(PPh3)4 (43 mg, 0.04 mmol), and CuI (88 mg, 0.46 mmol).
After being stirred overnight, the reaction mixture was filtered
through a thin pad of silica, eluting with Et2O, and then
concentrated. Purification on silica by radial chromatography
(0.1% Et3N in hexanes) provided 12 (161 mg, 94%) as a yellow
oil: 1H NMR (CD2Cl2) δ 7.52-7.49 (AA′m, 2H), 7.34-7.31
(BB′m, 2H), 6.17 (d, J ) 10.9, 2H), 5.94 (d, J ) 10.9, 2H), 0.22
(s, 18H); 13C NMR (CD2Cl2) δ 132.98, 129.07, 125.86, 120.96,
120.39, 104.25, 102.59, 96.31, 91.54, 0.11; IR (neat) ν 3057,
3028, 2191, 2143, 1478, 1443 cm-1; UV-vis (CH2Cl2) λmax (ꢀ)
267 (9800), 300 (16800), 337 (14400) nm; MS (ES+) m/z (rel
intens) 388.2 (55, M+ + H2O), 371.2 (25, M+ + H), 279.1 (100).
Deh yd r oben zo[14]a n n u len e 2. R,ω-Polyyne 12 (47 mg,
0.13 mmol) was dissolved in MeOH/THF (25 mL, 1:1 v/v), and
saturated K2CO3 solution (2 mL) was added. The mixture was
stirred for 2-3 h and monitored by TLC. Upon completion,
the reaction was diluted with Et2O, washed successively with
saturated NH4Cl solution, brine, and H2O, dried (MgSO4), and
filtered. Concentration of the product gave the free tetrayne
in sufficiently pure form and nearly quantitative yield.
The resulting tetrayne was dissolved in MeCN (40 mL), and
Cu(OAc)2 (346 mg, 1.90 mmol) was added. The blue-green
slurry was stirred at reflux for 24 h. After cooling, the reaction
mixture was diluted with Et2O, washed with H2O, dried
(MgSO4), filtered, and concentrated. The annulene quickly
polymerized in neat form to furnish an insoluble black film
(14.8 mg, 51%) (dilute solutions of 2 can be stored for several
weeks at rt): 1H NMR (CD2Cl2) δ 8.29-8.26 (AA′m, 2H), 7.74-
7.70 (BB′m, 2H), 7.41 (d, J ) 10.0, 2H), 6.73 (d, J ) 10.0, 2H);
13C NMR (CD2Cl2) δ 136.28, 128.84, 126.72, 122.91, 116.91,
100.01, 93.82, 90.38, 84.84; IR (CH2Cl2) ν 3189, 3053, 2117,
1470 cm-1; UV-vis (CH2Cl2, qualitative) λmax 234, 299, 308,
387 nm; MS (ES+) m/z (rel intens) 242.3 (100, M+ + H2O).
11.88, -0.02; IR (neat) ν 3060, 3043, 3028, 2157, 2141 cm-1
;
UV-vis (CH2Cl2) λmax (ꢀ) 252 (22600), 262 (22050), 291 (12850),
349 (21900) nm; MS (ES+) m/z (rel intens) 455.2 (100, M+).
Deh yd r oben zo[14]a n n u len e 3. R,ω-Polyyne 15 (34 mg,
0.07 mmol) was dissolved in THF (20 mL), and two drops of
MeOH was added. To this solution was added Bu4NF (1.0 M
in THF, 0.19 mL) in one portion, and the reaction was
monitored by TLC. Upon completion, the mixture was diluted
with Et2O, washed successively with saturated NH4Cl solution,
brine, and H2O, dried (MgSO4), and filtered. Concentration of
the product gave the deprotected tetrayne in sufficiently pure
form and nearly quantitative yield.
The resultant tetrayne was dissolved in MeCN (150 mL),
and Cu(OAc)2‚H2O (279 mg, 1.40 mmol) was added. The blue-
green slurry was stirred at reflux for 24 h. After cooling, the
reaction mixture was diluted with Et2O, washed with H2O,
dried (MgSO4), filtered, and concentrated. The annulene
polymerized upon concentration to give an insoluble brown
solid (dilute solutions of 3 can be stored for several weeks at
-20 °C): 1H NMR (CD2Cl2) δ 8.23 (dd, J ) 7.1, 2.0, 1H), 8.01
(dd, J ) 6.9, 2.1, 1H), 7.79-7.69 (m, 2H), 7.24 (dd, J ) 10.2,
3.3, 1H), 7.16 (d, J ) 11.7, 1H), 7.03 (dd, J ) 11.7, 3.3, 1H),
6.73 (d, J ) 10.2, 1H); 13C NMR (CD2Cl2) δ 133.81, 130.14,
129.31, 129.00, 128.63, 126.04, 122.98, 118.65, 116.91, 99.37,
98.21, 98.14, 93.08, 88.98, 87.53, 85.52, 81.00; IR (CH2Cl2) ν
3054, 2306, 2253, 1469, 1422 cm-1; UV-vis (CH2Cl2, qualita-
tive) λmax 229, 294, 302, 312, 359, 385 nm; MS (ES+) m/z (rel
intens) 242.3 (100, M+ + H2O).
r,ω-P olyyn e 17. Iodoarene 164b (200 mg, 0.41 mmol) was
dissolved in MeOH (55 mL) and Et3N (55 mL), and K2CO3 (57
mg, 0.41 mmol) was added. The reaction mixture was degassed
by N2 bubbling for 90 min. To this solution were added
enediyne 9 (131 mg, 0.45 mmol), PdCl2(PPh3)2 (9 mg, 0.01
mmol), and CuI (23 mg, 0.12 mmol), and the reaction was
stirred at 50 °C for 48 h. After cooling, the mixture was
concentrated, redissolved in Et2O, filtered through a thin pad
of silica, and concentrated again. Purification by column
chromatography on silica (5% CH2Cl2 in hexanes) provided 17
(193 mg, 75%) as a dark orange oil: 1H NMR (CD2Cl2) δ 7.57-
7.52 (m, 4H), 7.35-7.30 (m, 4H), 6.15 (d, J ) 10.8, 1H), 5.95
(d, J ) 10.8, 1H), 1.68 (sept, J ) 7.0, 1H), 1.14 (s, 21H), 0.90
(s, 6H), 0.87 (d, J ) 7.0, 6H), 0.19 (s, 6H); 13C NMR (CD2Cl2)
En etr iyn e 14. Phenyldiyne 134b (90 mg, 0.32 mmol) was
dissolved in THF (50 mL) and PrNH2 (0.05 mL, 0.64 mmol)
and the mixture degassed by N2 bubbling for 60 min. To this
were added (Z)-(4-chloro-3-buten-1-ynyl)trimethylsilane (101
mg, 0.64 mmol), Pd(PPh3)4 (18 mg, 0.02 mmol), and CuI (61
mg, 0.32 mmol). After being stirred overnight, the reaction
mixture was concentrated and redissolved in hexanes. The
slurry was filtered through silica (hexanes) to give enetriyne
8818 J . Org. Chem., Vol. 67, No. 25, 2002

Diatropicity of Octadehydro[14]annulenes
δ 133.29, 132.63, 132.46, 128.85, 128.75, 128.69, 126.28,
126.16, 120.65, 120.47, 105.84, 104.17, 103.53, 96.32, 95.81,
93.12, 92.30, 91.51, 35.13, 21.07, 19.09, 19.02, 11.96, -2.13;
vis (CH2Cl2, qualitative) λmax 229, 295 sh, 304, 383 nm; MS
(ES+) m/z (rel intens) 269.0 (50, M + K+), 231.1 (22, M+), 150
(21, M - C4H2S).
IR (neat) ν 3067, 3020, 2154, 2144, 1489, 1463, 1446 cm-1
;
r,ω-P olyyn e 23. 2,3-Bis(trimethylsilylethynyl)thiophene27
(184 mg, 0.67 mmol) was dissolved in MeOH/THF (50 mL, 1:1
v/v), and K2CO3 (460 mg, 3.33 mmol) was added. The depro-
tection was monitored by TLC. Upon completion, the reaction
mixture was diluted with Et2O, washed successively with
saturated NH4Cl solution, brine, and H2O, dried (MgSO4), and
filtered. Concentration of the product gave the free diethynyl-
thiophene in sufficiently pure form and nearly quantitative
yield.
UV-vis (CH2Cl2) λmax (ꢀ) 238 (38200), 263 (32300), 297 (26000),
321 (22250), 327 (22250) nm; MS (ES+) m/z (rel intens) 525.1
(7, M+ + H), 205.2 (100).
Deh yd r oben zo[14]a n n u len e 4. Tetrayne 17 (87 mg, 0.15
mmol) was dissolved in THF (20 mL), and three drops of
MeOH was added. To this solution was added Bu4NF (1.0 M
in THF, 0.38 mL) in one portion, and the reaction was stirred
for 3 h. Upon completion, the mixture was diluted with Et2O,
washed successively with saturated NH4Cl solution, brine, and
H2O, dried (MgSO4), and filtered. Concentration of the product
gave the deprotected tetrayne in sufficiently pure form and
nearly quantitative yield.
The tetrayne was dissolved in MeCN (150 mL), and Cu-
(OAc)2 (545 mg, 3.00 mmol) was added. The blue-green slurry
was stirred at reflux for 24 h. After cooling, the reaction
mixture was diluted with Et2O, washed with H2O, dried
(MgSO4), filtered, and concentrated. The annulene polymerized
upon concentration to give an insoluble brown solid (dilute
solutions of 4 can be stored for several weeks at rt): 1H NMR
(CD2Cl2) δ 8.12 (dd, J ) 7.0, 1.8, 1H), 8.09 (dd, J ) 6.6, 1.8,
1H), 7.99 (dd, J ) 7.1, 1.8, 1H), 7.76 (dd, J ) 7.5, 1.5, 1H),
7.64-7.53 (m, 4H), 7.01 (d, J ) 10.3, 1H), 6.37 (d, J ) 10.3,
1H); 13C NMR (CD2Cl2) δ 136.64, 136.27, 133.98, 129.80,
129.51, 129.40, 129.04, 128.73, 128.69, 127.00, 123.86, 122.84,
122.39, 117.42, 99.33, 98.62, 94.25, 93.88, 92.93, 87.37, 84.37,
80.34; IR (CH2Cl2) ν 3053, 2302, 2196, 1492 cm-1; UV-vis
(CH2Cl2, qualitative) λmax 230, 255, 271, 295, 306, 313, 355,
383 nm; MS (ES+) m/z (rel intens) 292 (7, M+ + H2O), 186.3
(100).
r,ω-P olyyn e 21. 3,4-Diiodothiophene (69 mg, 0.21 mmol),
K2CO3 (232 mg, 1.68 mmol), MeOH (4 mL), i-Pr2NEt (0.22 mL,
1.26 mmol), and THF (10 mL) were added to a glass pressure
tube. After the mixture was degassed by N2 bubbling for 30
min, 1-(triisopropylsilyl)-6-(trimethylsilyl)-1,5-hexadiyn-3-ene26
(384 mg, 1.26 mmol), Pd(PPh3)4 (24 mg, 0.02 mmol), and CuI
(8 mg, 0.04 mmol) were added. The tube was sealed and the
reaction stirred at 100 °C for 24 h. After cooling, the mixture
was diluted with hexanes and washed successively with 10%
HCl solution, brine, and H2O. The organic layer was dried
(MgSO4), filtered through a thin pad of silica (hexanes), and
concentrated. Purification of the crude oil by column chroma-
tography on silica (0.1% Et3N in hexanes) gave 21 (77 mg, 67%)
as an orange oil: 1H NMR (CDCl3) δ 7.34 (s, 2H), 6.07 (d, J )
10.9, 2H), 5.91 (d, J ) 10.9, 2H), 1.10 (s, 42H); 13C NMR
(CDCl3) δ 128.63, 124.64, 120.19, 119.72, 103.95, 99.97, 90.54,
89.09, 18.65, 11.24; IR (neat) ν 3112, 3053, 2942, 2865, 2201,
2142, 1463, 1434 cm-1; UV-vis (CH2Cl2) λmax (ꢀ) 291 (21900),
311 (24150), 333 (22450) nm; MS (ES+) m/z (rel intens) 562.3
(100, M+ + H2O), 545.3 (38, M+ + H).
The deprotected diyne was dissolved in THF (50 mL) and
PrNH2 (0.27 mL, 3.33 mmol), and the mixture was degassed
by N2 bubling for 60 min. To this were added (Z)-(4-chloro-3-
buten-1-ynyl)trimethylsilane (528 mg, 3.33 mmol), Pd(PPh3)4
(77 mg, 0.07 mmol), and CuI (128 mg, 0.67 mmol). After being
stirred overnight, the reaction mixture was filtered through a
thin pad of silica (10% CH2Cl2 in hexanes) and concentrated.
Purification by column chromatography on silica (0.1% Et3N,
10% CH2Cl2 in hexanes) provided 23 (139 mg, 55%) as a light
orange oil: 1H NMR (CDCl3) δ 7.22 (d, J ) 5.3, 1H), 7.02 (d,
J ) 5.3, 1H), 6.12 (d, J ) 10.8, 1H), 6.10 (d, J ) 10.8, 1H),
5.90 (d, J ) 10.8, 1H), 5.89 (d, J ) 10.8, 1H), 0.24 (s, 9H), 0.23
(s, 9H); 13C NMR (CDCl3) δ 130.07, 127.05, 126.40, 120.48,
120.19, 119.66, 119.48, 104.27, 103.72, 102.09, 101.99, 95.46,
91.56, 90.97, 89.45, -0.11; IR (neat) ν 3109, 3043, 2958, 2198,
2144, 1404 cm-1; UV-vis (CH2Cl2) λmax (ꢀ) 256 (14700), 279
(13450), 308 (18000), 361 (18700) nm; MS (ES+) m/z (rel intens)
377.1 (90, M+), 263.1 (100).
Deh yd r oth ien o[14]a n n u len e 8. A mixture of tetrayne 23
(15 mg, 0.04 mmol), Cu(OAc)2‚H2O (160 mg, 0.80 mmol), and
K2CO3 (28 mg, 0.20 mmol) was dissolved in MeOH/MeCN (50
mL, 1:1 v/v). The blue-green slurry was stirred at reflux for
24 h. After cooling, the reaction mixture was diluted with Et2O,
washed with H2O, dried (MgSO4), filtered, and concentrated.
The annulene polymerized upon concentration to give an
insoluble brown solid (dilute solutions of 8 can be stored for
2-3 weeks at -20 °C): 1H NMR (CDCl3) δ 7.81 (d, J ) 5.4,
1H), 7.69 (d, J ) 5.4, 1H), 7.60 (d, J ) 9.9, 1H), 7.58 (d, J )
9.9, 1H), 7.02 (d, J ) 10.2, 1H), 6.97 (d, J ) 10.2, 1H); 13C
NMR (CDCl3) δ 131.97, 127.96, 124.92, 124.60, 124.22, 116.50,
115.81, 99.25, 95.62, 94.05, 93.41, 90.07, 89.90, 85.63, 85.11;
IR (neat) ν 3055, 2987, 2305, 2253, 1422 cm-1; UV-vis (CH2-
Cl2, qualitative) λmax 302 sh, 318, 357 nm; MS (ES+) m/z (rel
intens) 269.0 (63, M + K+), 187.0 (60), 105.1 (100).
Ack n ow led gm en t. We thank the Petroleum Re-
search Fund (M.M.H.), administered by the American
Chemical Society, 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.
Deh yd r oth ien o[14]a n n u len e 7. R,ω-Polyyne 21 (65 mg,
0.12 mmol) was dissolved in THF (30 mL), and two drops of
MeOH was added. To this was added Bu4NF (1.0 M in THF,
0.19 mL) in one portion, and the reaction was stirred for 2.5
h. Upon completion, the mixture was diluted with Et2O,
washed successively with saturated NH4Cl solution, brine, and
H2O, dried (MgSO4), and filtered. Concentration of the product
gave the deprotected tetrayne in sufficiently pure form and
nearly quantitative yield.
The above tetrayne was dissolved in MeCN (120 mL), and
Cu(OAc)2‚H2O (479 mg, 2.40 mmol) was added. The blue-green
slurry was stirred at reflux for 24 h. After cooling, the reaction
mixture was diluted with Et2O, washed with H2O, dried
(MgSO4), filtered, and concentrated. The annulene polymerized
upon concentration to give an insoluble brown solid (dilute
solutions of 7 can be stored for 2-3 weeks at -20 °C): 1H NMR
(CDCl3) δ 8.01 (s, 2H) 6.93 (d, J ) 10.2, 2H), 6.32 (d, J ) 10.2,
2H); 13C NMR (CDCl3) δ 131.61, 126.13, 122.59, 116.42, 93.44,
90.85, 88.43, 83.96; IR (CH2Cl2) ν 3007, 2257, 2244 cm-1; UV-
Su p p or tin g In for m a tion Ava ila ble: Calculated and
experimental bond lengths for 1-8 and 24 (Table S1), 1H NMR
experimental and calculated (using the GIAO-HF/6-31G*//
B3LYP/6-31G* method) chemical shifts of 1-8 and 24 (Tables
S2 and S3), 13C NMR experimental and calculated (using the
GIAO-B3LYP/6-31G*//B3LYP/6-31G* method and scaled using
the method of Forsyth and Sebag36) chemical shifts of 1-8 and
24 (Tables S4-S5), NICS values for compounds 1-8, 24, and
25 (Table S6), Cartesian coordinates of 2-8 and 25 (coordi-
nates for 1 and 24 are part of the Supporting Information for
the accompanying paper5) optimized using the B3LYP/6-31G*
method, and 13C NMR spectra for compounds 1-4, 7-8, 10,
12, 14-15, 17, 21, and 23. This material is available free of
charge via the Internet at http://pubs.acs.org.
J O020463I
(36) Forsyth, D. A.; Sebag, A. B. J . Am. Chem. Soc. 1997, 119, 9483-
9494.
J . Org. Chem, Vol. 67, No. 25, 2002 8819