ORGANIC
LETTERS
2012
Vol. 14, No. 23
6032–6035
Polyaromatic Ribbon/Benzofuran
Fusion via Consecutive Endo
Cyclizations of Enediynes
Philip M. Byers, Julian I. Rashid, Rana K. Mohamed, and Igor V. Alabugin*
Department of Chemistry and Biochemistry, Florida State University, Tallahassee,
Florida 32306-4390, United States
Received October 23, 2012
ABSTRACT
The Sonogashira/5-endo-dig/6-endo-dig cascade fuses a polycyclic aromatic backbone to the electron-rich furan subunit. The transformation
proceeds in modest yields as a one-pot reaction. Efficiency of the full cascade is increased by removal of base prior to the addition of gold catalyst.
Under these conditions, conversion to the full cascade products is achieved in nearly quantitative yields without purification of the intermediate
products. Extension of the cascade toward triynes opens access to benzofuran-fused chrysene derivatives.
Alkynes are valuable precursors for the preparation of
carbon-rich materials1 due to their high carbon content,
modular assembly via reliable cross-coupling chemistry,
and propensity for participating in coordinated and effi-
cient cascade transformations leading to the construction
ofpolycyclic frameworks.2 Heteroatom incorporation into
polycyclic aromatic frameworks fine-tunes their electronic
properties, leadingtomajoradvancesinthe field of organic
materials. Annealing of donor heterocycles can expand
the utility of carbon-rich compounds in materials3,4 and
molecular devices.5
As a continuation of our work on alkyne cyclizations,6
we recently reported a cascade transformation of four
alkynes into extended polyaromatic structures through a
(4) Selected examples from special issue on organic electronics:
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(6) Selected recent examples: (a) Alabugin, I. V.; Gilmore, K.; Patil,
S.; Manoharan, M.; Kovalenko, S. V.; Clark, R. J.; Ghiviriga, I. J. Am.
Chem. Soc. 2008, 130, 11535. (b) Vasilevsky, S. F.; Baranov, D. S.;
Mamatyuk, V. I.; Gatilov, Y. V.; Alabugin, I. V. J. Org. Chem. 2009, 74,
6143. (c) Baranov, D. S.; Vasilevsky, S. F.; Gold, B.; Alabugin, I. V. RSC
Adv. 2011, 1, 1745. (d) Gilmore, K.; Manoharan, M.; Wu, J.; Schleyer, P.
v.R.; Alabugin, I. V. J. Am. Chem. Soc. 2012, 134, 10584.
(7) Alabugin, I. V.; Gilmore, K.; Patil, S.; Manoharan, M.; Kova-
lenko, S. V.; Clark, R. J.; Ghiviriga, I. J. Am. Chem. Soc. 2008, 130,
11535. Intramolecular initiation via the “weak link” design: Byers,
P. M.; Alabugin, I. V. J. Am. Chem. Soc. 2012, 134, 9609.
(8) (a) Nevado, C.; Echavarren, A. M. Chem.;Eur. J. 2005, 11, 3155.
(b) Gilmore, K.; Alabugin, I. V. Chem. Rev. 2011, 111, 6513. (c)
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(3) (a) Anthony, J. E. Chem. Mater. 2011, 23, 583. (b) Scharber,
€
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r
10.1021/ol302922t
Published on Web 11/28/2012
2012 American Chemical Society