Versatile synthetic route to and DSC analysis of dehydrobenzoannulenes: Crystal structure of a heretofore inaccessible [20]annulene derivative

Full text of DOI:10.1021/ja964048h

2956
J. Am. Chem. Soc. 1997, 119, 2956-2957
Versatile Synthetic Route to and DSC Analysis of
Dehydrobenzoannulenes: Crystal Structure of a
Heretofore Inaccessible [20]Annulene Derivative
Michael M. Haley,* Michael L. Bell, Jamieson J. English,
Charles A. Johnson, and Timothy J. R. Weakley†
Department of Chemistry
UniVersity of Oregon, Eugene, Oregon 97403
ReceiVed NoVember 25, 1996
The synthesis and chemistry of dehydroannulenes and their
benzannelated analogs, although extensively explored during
the Sondheimer era,1 has experienced a vigorous resurgence over
the last few years.2,3 Much of the renewed interest can be
attributed to the recognition that these compounds can potentially
serve as precursors for a variety of technologically important,
carbon-rich molecular and polymeric systems, such as novel
allotropes of carbon, molecular scaffolds, and ladder polymers.2-4
To systematically study the reaction chemistry and possible
materials properties, researchers need easy access to differing
topologies of dehydrobenzoannulenes on greater than milligram
scale. Traditional syntheses of the macrocycles have involved
copper-mediated dimerization/cyclooligomerization reactions of
suitable R,ω-diacetylenes.5 While simple in design and execu-
tion, these reactions typically lead to complex mixtures of
products that are difficult to separate and often provide low
isolated yields of a given macrocycle. Additionally, the
variation of product structure is severely limited by the ease of
construction (or lack thereof) of the starting diyne. We report
herein a simple, one-pot procedure that allows preparation of
novel R,ω-polyynes, thus leading to dehydrobenzoannulenes of
varying topologies previously available only in low yield (26
and 53b) or altogether inaccessible by traditional routes (1, 3,
and 4).7
In order to ensure formation of a single product, an intramo-
lecular dimerization of R,ω-polyynes was envisaged to prepare
1-5. Synthesis of each polyyne would necessitate use of a
suitably functionalized phenylbutadiyne. Unfortunately, the
parent molecule, 1-phenyl-1,3-butadiyne, is a highly reactive
compound which polymerizes rapidly when neat or in concen-
trated solution; even a dilute solution at -20 °C polymerizes
within a few hours.8 This extreme reactivity has limited the
synthetic utility of phenylbutadiynes to date. Indeed, all of our
attempts to use unprotected phenylbutadiynes in Pd-catalyzed
alkynylation reactions provided intractable polymeric gums.
Other approaches have been developed that formally introduce
a phenylbutadiyne moiety; however, these are multistep conver-
sions with low overall yields.9
To avoid the forementioned problems, we found that in situ
generation of phenylbutadiynes gave very good to excellent
yields of coupled products.10 The route to annulene 1, depicted
in Scheme 1, illustrates the technique. 1-Bromo-2-iodoben-
zene11 served as the cornerstone for construction of multigram
quantities of both iodoarene 6 and butadiyne synthon 7 by
repetitive alkynylation,12 desilylation,13 and/or iodination14
methods. Slow addition of 7 to a vigorously stirred, degassed
solution of 6 using the deprotection/alkynylation conditions (step
g) furnished pentayne 8 in 84% yield. Extension of this reaction
sequence to other iodoarenes provided a series of bis(triisopro-
pylsilyl)-protected R,ω-poliynes in very good yields (Table 1).
Subsequent desilylation of 8 with Bu4NF and cyclization with
Cu(OAc)25 under pseudo-high dilution conditions provided pale
yellow needles of 1 as the sole product in 40% overall yield. In
a similar manner annulenes 2-5 were obtained, albeit in more
modest overall yields (25-30%).16 Macrocycles 1-5 are
remarkably stable, showing little or no decomposition over
several weeks in solution or in the crystalline state.
† Author to whom inquiries about the X-ray crystal structure should be
addressed.
(1) For a comprehensive review of annulene chemistry, see: Balaban,
A. T.; Banciu, M.; Ciorba, V. Annulenes, Benzo-, Hetero-, Homo-
DeriVatiVes and their Valence Isomers; CRC Press: Boca Raton, 1987;
Vols. 1-3.
(2) Dehydroannulenes: (a) Diederich, F. Nature (London) 1994, 369,
199-207. (b) Diederich, F. In Modern Acetylene Chemistry; Stang, P. J.,
Diederich, F., Eds.; VCH: Weinheim, 1995. (c) Tobe, Y.; Fulii, T.;
Matsumoto, H.; Naemura, K.; Achiba, Y.; Wakabayashi, T. J. Am. Chem.
Soc. 1996, 118, 2758-2759. (d) Tobe, Y.; Matsumoto, H.; Naemura, K.;
Achiba, Y.; Wakabayashi, T. Angew. Chem., Int. Ed. Engl. 1996, 35, 1800-
1802.
(3) Dehydrobenzoannulenes: (a) Zhou, Q.; Carroll, P. J.; Swager, T. M.
J. Org. Chem. 1994, 59, 1294-1301. (b) Guo, L.; Bradshaw, J. D.; Tessier,
C. A.; Youngs, W. J. J. Chem. Soc., Chem. Commun. 1994, 243-244. (c)
Baldwin, K. P.; Simons, R. S.; Rose, J.; Zimmerman, P.; Hercules, D. M.,
Tessier, C. A.; Youngs, W. J. J. Chem. Soc., Chem. Commun. 1994, 1257-
1258. (d) Baldwin, K. P.; Matzger, A. J.; Scheiman, D. A.; Tessier, C. A.;
Vollhardt, K. P. C.; Youngs, W. J. Synlett 1995, 1215-1218. (e) Kuwantani,
Y.; Ueda, I. Angew. Chem., Int. Ed. Engl. 1995, 34, 1892-1894. (f) Kawase,
T.; Darabi, H. R.; Oda, M. Angew. Chem., Int. Ed. Engl. 1996, 35, 2664-
2666.
(4) (a) Young, J. K.; Moore, J. S. in Modern Acetylene Chemistry, Stang,
P. J.; Diederich, F., Eds.; VCH: Weinheim, 1995. (b) Bunz, U. H. F. Angew.
Chem., Int. Ed. Engl. 1994, 33, 1073-1076. (c) Baughman, R. H.; Galvao,
D. S.; Cui, C.; Wang, Y.; Tomanek, D. Chem. Phys. Lett. 1993, 204, 8-14.
(d) Baughman, R. H.; Eckhardt, H.; Kerte´sz, M. J. Chem. Phys. 1987, 87,
6687-6699. (e) Rubin, Y.; Parker, T. C.; Khan, S. I.; Holliman, C. L.;
McElvany, S. W. J. Am. Chem. Soc. 1996, 118, 5308-5309.
(5) (a) Glaser, C. Chem. Ber. 1869, 2, 422-424. (b) Hay, A. S. J. Org.
Chem. 1962, 27, 3320-3321. (c) Eglinton, G.; McRae, W. AdV. Org. Chem.
1963, 4, 225-328. (d) Vo¨gtle, F.; Berscheid, R. Synthesis 1992, 58-62.
(6) Boese, R.; Matzger, A. J.; Vollhardt, K. P. C. J. Am. Chem. Soc.
1997, 119, 2052-2053. We thank Professor Vollhardt for sharing this
information prior to publication.
(8) Brandsma, L. PreparatiVe Acetylenic Chemistry, Elsevier: Amster-
dam, 1971. The first edition contained the preparation of 1-phenyl-1,3-
butadiyne, but stated that “...the compound proved to be very unstable, (and)
can be stored at -20 °C for a very limited period.” This procedure has
subsequently been deleted from the second edition (1988).
(9) Bryant-Friedrich, A.; Neidlein, R. Synthesis 1996, 1506-1510.
(10) Although in situ generation of alkynes under palladium-catalyzed
coupling conditions is known, the previous examples were highly stable,
monoacetylenic systems. See: (a) Rossi, R.; Carpita, A.; Lezzi, A.
Tetrahedron 1984, 40, 2773-2779. (b) Carpita, A.; Lezzi, A.; Rossi, R.
Synthesis 1984, 571-572. (c) Huynh, C.; Linstrumelle, G. Tetrahedron
1988, 44, 6337-6344. (d) D’Auria, M. Synth. Commun. 1992, 22, 2393-
2399.
(11) Heaney, H.; Millar, I. T.; Roberts, J. D.; Montgomery, L. K. Organic
Syntheses; Wiley: New York, 1973; Collect. Vol. V, pp 1120-1123. The
molecule is also available from several commercial sources.
(12) Heck, R. F. Palladium Reagents in Organic Syntheses; Academic
Press: London, 1985.
(13) Colvin, E. W. Silicon Reagents in Organic Synthesis; Academic
Press: London, 1988.
(7) A detailed account of the synthesis of closely related dodecadehydro-
tribenzo[18]annulene and several derivatives in connection to the hypotheti-
cal, all-carbon polymeric network graphdiyne has been reported else-
where: Haley, M. M.; Brand, S. C.; Pak, J. J. Angew. Chem., Int. Ed. Engl.
1997, 36, in press.
(14) Moore, J. S.; Weinstein, E. J.; Wu, Z. Tetrahedron Lett. 1991, 32,
2465-2466.
(15) Whitlock, B. J.; Whitlock, H. W. J. Org. Chem. 1972, 37, 3559-
3561.
S0002-7863(96)04048-6 CCC: $14.00 © 1997 American Chemical Society

Communications to the Editor
J. Am. Chem. Soc., Vol. 119, No. 12, 1997 2957
Scheme 1a
Table 1. Reactants and Yields
Figure 1. X-ray crystal structure of dehydrobenzoannulene 3.
Table 2. DSC Data for Annulenes 1-5a
annulene
Tonset (°C)
Tmax (°C)
w1/2 (°C)
∆Hrxn (kJ mol-1
)
1
2
3
4
5
135
248
197
176
177
142
265
211
193
187
4
11
8
9
6
282
385
440
495
482
a Data obtained under an N2 atmosphere.
Recent results from Vollhardt’s group suggest two differing
pathways for dehydrobenzoannulene decomposition. In par-
ticular, spectroscopic evidence strongly suggested that highly
strained, planar, octadehydrotribenzo[14]annulene underwent
topochemical polymerization at 120 °C to give a novel poly-
diacetylene tube structure.3d Alternately, nonplanar tetrabenzo
molecule 2 decomposed explosively at ca. 250 °C to give a
nearly pure carbon residue that included “bucky tubes” and
“bucky onions”.6,18 In contrast, isomeric 3 reacted at 50 °C
lower temperature and generated 50 kJ mol-1 more energy.
Although this result can be attributed partly to the greater
bending in the alkyne units versus 2, the additional exothermicity
of 3 is likely due to the influence of other factors such as solid-
state packing.19 Clearly, the varying temperatures and heats of
reaction in Table 2 indicate that each annulenic system behaves
independently and that no generalization for accurately predict-
ing decomposition product structure based on annulene topology
can be proposed at this time. It is possible that the milder
polymerization temperatures for 3-5 might lead to alternate
pathways for dehydrobenzoannulene decomposition. It therefore
appears that systematic study of the thermoproducts of each
new macrocycle is warranted; this goal is being actively pursued.
Examination of the solid-state structure and behavior of the
macrocycles should provide some insight into the thermal
stability of this class of annulenes. Accordingly, we obtained
X-ray crystal structures for all of the new annulenes; the
structure of compound 3 is shown in Figure 1. The molecule
possesses a distorted saddle shape, with the alkyne moieties
showing a deviation from linearity on the order of 1.5-8.1°.
This range is slightly greater than the deformation observed in
5 (0.6-6.0°)3b and considerably more so than in isomeric
annulene 2 (0.6-3.9°).6 Semiempirical calculations accurately
reproduce these geometrical observations.17
Acknowledgment. We acknowledge the donors of The Petroleum
Research Fund, administered by the ACS, and the University of Oregon
for generous support of this research. We thank Robert Schneidmiller
for obtaining DSC data. M.M.H. gratefully acknowledges the NSF
for a CAREER Award (1995-1998).
Thermal analysis of macrocycles 1-5 showed the molecules
to be extremely reactive. All of the annulenes underwent
irreversible exothermic reaction prior to melting (ca. 175-250
°C) as determined by differential scanning calorimetry (Table
2). Dehydrobenzo[16]annulene 1 was the notable exception,
reacting around 135 °C; this was undoubtedly due to the ring
strain in the constricted annulenic core. The black thermal
products were completely insoluble in common solvents.
Supporting Information Available: General experimental proce-
dures, spectral data for 1-8, X-ray structure of 3, tables of atomic
coordinates, thermal parameters, bond lengths, and bond angles (14
pages). See any current masthead page for ordering information and
Internet access instructions.
JA964048H
(18) Dresselhaus, M. S.; Dresselhaus, G.; Eklund, P. C. Science of
Fullerenes and Carbon Nanotubes; Academic Press: San Diego, 1996.
(19) Previous studies of the polymerization of cyclic diacetylenes with
comparatively low ring strain have concluded that solid-state packing was
more important than ring strain effects; see: Baughman, R. H.; Yee, K. C.
J. Polym. Sci.: Polym. Chem. 1974, 12, 2467-2475. The importance of
solid-state packing has been observed for highly strained systems as well.3a
(16) To date, we have limited the scale-up of the reactions to production
of 500-750 mg of annulene per run, yet have observed only a minor
decrease in yields.
(17) MNDO and PM3 calculations performed on a SGI workstation using
Spartan molecular modeling software (version 4.1.1).