Perylene synthesis by the parallel cycloaromatization of adjacent enediynes

Article abstract of DOI:10.1021/ol005615f

(equation presented) As part of an investigation into new synthetic routes to poly(peri-naphthalene), the synthesis and cycloaromatization of tetraethynylbiphenyls is described. The temperature-dependent cyclization of biphenyls containing unsubstituted a

Full text of DOI:10.1021/ol005615f

ORGANIC
LETTERS
2000
Vol. 2, No. 7
961-963
Perylene Synthesis by the Parallel
Cycloaromatization of Adjacent
Enediynes
Siew-Yin Chow, Grant J. Palmer, Daniel M. Bowles, and John E. Anthony*
Department of Chemistry, UniVersity of Kentucky, Lexington, Kentucky 40506-0055
anthony@pop.uky.edu
Received February 2, 2000
ABSTRACT
As part of an investigation into new synthetic routes to poly(peri-naphthalene), the synthesis and cycloaromatization of tetraethynylbiphenyls
is described. The temperature-dependent cyclization of biphenyls containing unsubstituted alkynes provides the desired perylene in good
yield.
A promising target for the preparation of conducting organic
polymers is poly(peri-naphthalene) (PPN, 2). Numerous
Scheme 1
theoretical treatments of this system have predicted a low
band gap for the polymer,1 while attempted syntheses of this
material by the vacuum-pyrolysis of 3,4,9,10-perylenetetra-
carboxylic dianhydride2 have provided insoluble, yet air-
stable materials with conductivities as high as 1100 S cm-1.
While no synthesis of substituted, characterizable derivatives
of this polymer have been reported, solubilized oligomeric
species (called rylenes3) have been prepared from oligo-
naphthalene precursors by reductive coupling with potassium
metal followed by oxidation, or by heating in an oxidative
alkali melt.4
Recent reports of the use of the Bergman cycloaromati-
zation reaction5 to prepare poly(p-phenylenes)6 and other
highly cross-linked phenylene systems7 (Scheme 1, A) have
(1) (a) Tanaka, K.; Ueda, K.; Koike, T.; Yamabe, T. Solid State Commun.
1984, 51, 943. (b) Bre´das, J. L.; Baughman, R. H. J. Chem. Phys. 1985,
83, 1316. (c) Bakhshi, A. K.; Ladik, J. Synth. Met. 1989, 30, 115. (d)
PPN and its oligomers (Scheme 1, B) which utilizes the
Viruela-Martin, R.; Viruela-Martin, P. M.; Orti, E. J. Chem. Phys. 1992,
led us to consider an alternative method for the synthesis of
97, 8470. (e) Karabunarliev, S.; Baumgarten, Mu¨llen, K.; Tyutyulkov, N.
Chem. Phys. 1994, 179, 421.
(2) (a) Kaplan, M. L.; Schmidt, P. H.; Chen, C.-H.; Walsh, W. M., Jr.
Appl. Phys. Lett. 1980, 36, 867. (b) Iqbal, Z.; Ivory, D. M.; Marti, J.; Bre´das,
J. L.; Baughman, R. H. Mol. Cryst. Liq. Cryst. 1985, 118, 103. (c)
Murakami, M.; Yoshimura, S. J. Chem. Soc., Chem. Commun. 1984, 1649.
(3) Clar, E. Chem. Ber. 1948, 81, 52.
(4) (a) Koch, K.-H.; Mu¨llen, K. Chem. Ber. 1991, 124, 2091. (b) Holtrup,
F. O.; Mu¨ller, G. R. J.; Quante, H.; De Feyter, S.; De Schryver, F. C.;
Mu¨llen, K. Chem. Eur. J. 1997, 3, 219. (c) Quante, H.; Mu¨llen, K. Angew.
Chem., Int. Ed. Engl. 1995, 34, 1323.
(5) (a) Bergman, R. G. Acc. Chem. Res. 1973, 6, 25. (b) Lockhart, T.
P.; Commita, P. B.; Bergman, R. G. J. Am. Chem. Soc. 1981, 103, 4082.
10.1021/ol005615f CCC: $19.00 © 2000 American Chemical Society
Published on Web 03/04/2000

thermal cycloaromatization of polymeric or oligomeric
arenediynes such as 1 to form the desired PPN or rylene.
Because cycloaromatization is strictly a thermal process, this
parallel implementation of the reaction will be amenable to
a wide variety of functional groups on the arene unit, which
will allow the preparation of solubilized oligomers and
polymers. We report here our first model studies on the
synthesis and parallel cycloaromatization of some 2,3,2′,3′-
tetraethynylbiphenyls, the effects of substitution on the
cycloaromatization reaction, and the cyclization temperature
dependence for the formation of a 2,11-disubstituted perylene.
Substituted biphenyl tetrayne 7 was prepared in three high-
yielding steps from halogenated aniline 3.8 Diazotization/
iodination of 3 in acetic acid followed by selective palladium-
catalyzed alkyne coupling to the iodine functionalities led
to the bromo enediynes 5 and 6 in fair to good yields
(Scheme 2).
converted half of the material to the aryl iodide, and
anhydrous zinc chloride (0.6 equiv), which converted the
remaining aryllithium to the corresponding arylzinc species.
Addition of a palladium catalyst and heating to 60 °C
overnight provided the desired biphenyl in 81% isolated
yield. Biphenyl 7 was desilylated by treatment with sodium
methoxide in methanol-THF, yielding tetrayne 8 in quan-
titative yield. Cycloaromatization of 8, which required
heating a 0.01 M solution of the tetrayne in 10:1 (v/v)
benzene/1,4-cyclohexadiene to 180 °C in a sealed steel bomb9
for 2 h, led to the desired perylene 9 as the major product
(66% yield), along with a small amount (∼10%) of the
binaphthyl 10.10
While several reaction trials involving variations in the
concentration of the radical trap showed little change in the
ratio of these two products,11 the product distribution was
found to depend strongly on the reaction temperature (Table
1), with higher temperatures leading to increasing amounts
of the desired perylene.
Scheme 2
Table 1. Temperature Dependence of Product Distribution for
the Cycloaromatization of 8
temp (°C)
time (h)a
yield of 9, %
ratio 9:10
140
160
180
210
48
6
2
23b
51b
66c
40b
1:1.3
2:1
5:1
<2
7:1
a Time required for complete consumption of starting material. b GC
yield. c Isolated yield.
Enediyne 5 was homocoupled through a convenient one-
pot reaction sequence (Scheme 3). Halogen-metal exchange
A possible explanation for this temperature-dependent
product distribution arises from a consideration of the most
reasonable mechanism for the formation of perylene 9 from
8. Previous studies have shown that the radical species
formed by cycloaromatization react preferentially with other
cycloaromatized species, rather than with uncycloaromatized
enediyne.6b If biphenyl 8 behaves in an analogous manner,
both of the enediyne units in the biphenyl need to be in the
cycloaromatized state in order to form the perylene. Because
the rate of cycloaromatization increases with increasing
temperature, at higher temperature it is more likely that both
enediyne units on any single biphenyl will be in the
cycloaromatized state.12
Scheme 3
(7) Smith, D. W., Jr.; Babb, D. A.; Snelgrove, R. V.; Townsend, P. H.,
III; Martin, S. J. J. Am. Chem. Soc. 1998, 120, 9078.
(8) Ho¨ger, S.; Meckenstock, A.-D.; Pellen, H. J. Org. Chem. 1997, 62,
4556.
(9) All of the cycloaromatization reactions were performed in sealed
systems behind protective shielding.
(10) For confirmation of structure, compound 10 was also synthesized
by the homocoupling of 1-bromo-3-tert-butylnaphthalene, which was
prepared by the cycloaromatization of desilylated 5.
(11) Decreasing the concentration of the radical trap did lead to a
significant decrease in overall yield.
(12) An alternative mechanism involves a 6-exo radical attack of one
cycloaromatized enediyne unit on an alkyne on the adjacent, uncycloaro-
matized enediyne unit. Similar 6-exo radical cyclizations have been shown
to be particularly inefficient. See, for example: Grisson, J. W.; Calkins, T.
L.; Egan, M. J. Am. Chem. Soc. 1993, 115, 11744.
with 1.0 equiv of butyllithium in THF at -78 °C was
followed by the addition of 0.5 equiv of iodine, which
(6) (a) John, J. A.; Tour, J. M. J. Am. Chem. Soc. 1994, 116, 5011. (b)
John, J. A.; Tour, J. M. Tetrahedron 1997, 53, 15515.
962
Org. Lett., Vol. 2, No. 7, 2000

To further explore the scope and mechanism of parallel
cycloaromatization reactions, partially substituted tetrayne
12 was prepared. Because disubstituted enediynes do not
undergo cycloaromatization at reasonable temperatures,13 all
reaction products arising from the thermal reactions of
desilylated 11 will result from interactions of the substituted
enediyne unit with the adjacent cycloaromatized species.
Biphenyl 11 was synthesized by an asymmetric coupling
between bromo enediynes 5 and 6 as outlined in Scheme 4,
Desilylation of 11 followed by cycloaromatization using
conditions similar to those described for 8 led to naphthalene
13 as the sole isolable product in 20% yield, along with a
number of side products which appear to have resulted from
hydrogen abstraction from the alkyl side chains,14 and
significant uncharacterizable tarsthere was no evidence of
any reaction products arising from the interaction of the
cycloaromatized enediyne with the adjacent alkyne. The
complete absence of the desired perylene from the reaction
mixture has significant implications for the application of
parallel cycloaromatization to the formation of larger rylenes
or polymerssolubilizing groups on these larger systems will
have to be placed on the aromatic rings, rather than on the
more easily substituted alkynes. We are currently investigat-
ing the effects of ring substitution on the subsequent
cycloaromatization step, to be able to prepare larger oligo-
mers and solublilized polymer.
Scheme 4
Acknowledgment. The authors gratefully acknowledge
support of this project from the Camille and Henry Dreyfus
Foundation (New Faculty Award to J.E.A.), a NSF CAREER
Award (CHE9875123), and the Office of Naval Research.
Supporting Information Available: Text giving experi-
mental procedures for the preparation of compounds 4-7,
9-11, and 13, along with their 13C NMR spectra. This
material is available free of charge via the Internet at
http://pubs.acs.org.
OL005615F
providing the desired biphenyl 11 in acceptable yield along
with appreciable amounts of 7 as the major byproduct.
(14) Grissom, J. W.; Calkins, T. L.; Huang, S.; McMillen, H. Tetrahedron
1994, 50, 4635.
(13) Bowles, D. M.; Anthony, J. E. Org. Lett. 2000, 2, 85 and ref 5b.
Org. Lett., Vol. 2, No. 7, 2000
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