ORGANIC
LETTERS
2006
Vol. 8, No. 23
5361-5363
AuCl-Catalyzed [4+2] Benzannulation
between o-Alkynyl(oxo)benzene and
Benzyne
Naoki Asao*,†,‡ and Kenichiro Sato†
Department of Chemistry, and Research and Analytical Center for Giant Molecules,
Graduate School of Science, Tohoku UniVersity, Sendai 980-8578, Japan
Received September 14, 2006
ABSTRACT
The AuCl-catalyzed benzannulation of o-alkynyl(oxo)benzenes with benzenediazonium 2-carboxylate proceeds under mild conditions and a
variety of anthracene derivatives, having a ketone group at the 9-position, are produced in good to high yields. The reaction proceeds most
probably through the [4+2] cycloaddition between benzyne and benzopyrylium auric ate complex, which would be generated by the gold-
induced electrophilic cyclization of o-alkynyl(oxo)benzenes.
Benzynes are important reactive intermediates and many
studies on their reactions have been undertaken in synthetic
organic chemistry.1 Particularly, pericyclic cycloadditions
with benzyne, such as Diels-Alder reaction, are one of the
most important methods for the construction of polyaromatic
compounds.2 Due to its extraordinary reactive ability, the
reaction is observed with a very wide range of dienes
including simple benzene derivatives or other aromatic
compounds. The transition metal-catalyzed synthetic methods
of polyaromatics with benzynes have been also studied well.
However, to the best of our knowledge, there is no research
on the Lewis acid-catalyzed Diels-Alder reaction with
benzyne. We report here the AuCl-catalyzed formal [4+2]
benzannulation between o-alkynyl(oxo)benzenes and ben-
zenediazonium 2-carboxylate, which proceeds to give an-
thracene derivatives in good to high yields.3,4
(3) For highlights and reviews on the Au-catalyzed reactions, see: (a)
Dyker, G. Angew. Chem., Int. Ed. 2000, 39, 4237-4239. (b) Hashmi, A.
S. K. Gold Bull. 2003, 36, 3-9. (c) Hashmi, A. S. K. Gold Bull. 2004, 37,
51-65. (d) Arcadi, A.; Di Giuseppe, S. Curr. Org. Chem. 2004, 8, 795-
812. (e) Hoffmann-Ro¨der, A.; Krause, N. Org. Biomol. Chem. 2005, 3,
387-391. (f) Hashmi, A. S. K. Angew. Chem., Int. Ed. 2005, 44, 6990-
6993. (g) Ma, S.; Yu, S.; Gu, Z. Angew. Chem., Int. Ed. 2006, 45, 200-
203.
(4) Gold-catalyzed benzannulation, see: (a) Hashmi, A. S. K.; Frost, T.
M.; Bats, J. W. J. Am. Chem. Soc. 2000, 122, 11553-11554. (b) Hashmi,
A. S. K.; Frost, T. M.; Bats, J. W. Org. Lett. 2001, 3, 3769-3771. (c)
Dankwardt, J. W. Tetrahedron Lett. 2001, 42, 5809-5812. (d) Hashmi, A.
S. K.; Frost, T. M.; Bats, J. W. Catal. Today 2002, 72, 19-27. (e) Mamane,
V.; Hannen, P.; Fu¨rstner, A. Chem. Eur. J. 2004, 10, 4556-4575. (f)
Hashmi, A. S. K.; Rudolph, M.; Weyrauch, J. P.; Wo¨lfle, M.; Frey, W.;
Bats, J. W. Angew. Chem., Int. Ed. 2005, 44, 2798-2801. (g) Dyker, G.;
Hildebrandt, D. J. Org. Chem. 2005, 70, 6093-6096. (h) Shibata, T.;
Fujiwara, R.; Takano, D. Synlett 2005, 2062-2066. (i) Shibata, T.; Ueno,
Y.; Kanda, K. Synlett 2006, 411-414. (j) Zhao, J.; Hughes, C. O.; Toste,
F. D. J. Am. Chem. Soc. 2006, 128, 7436-7437. (k) Lian, J.-J.; Lin, C.-C.;
Chang, H.-K.; Chen, P.-C.; Liu, R.-S. J. Am. Chem. Soc. 2006, 128, 9661-
9667. (l) Hildebrandt, D.; Dyker, G. J. Org. Chem. 2006, 71, 6728-6733.
† Department of Chemistry.
‡ Research and Analytical Center for Giant Molecules.
(1) For reviews, see: (a) Hoffmann, R. W. Dehydrobenzene and
Cycloalkynes; Academic Press: New York, 1967. (b) Biehl, E. R.;
Khanapure, S. P. Acc. Chem. Res. 1989, 22, 275-281. (c) Kessar, S. V. In
ComprehensiVe Organic Synthesis; Trost, B. M., Fleming, I., Eds.; Pergamon
Press: New York, 1991; Vol. 4, pp 483-515. (d) Buchward, S. L.; Broene,
R. D. In ComprehensiVe Organometallic Chemistry II; Able, E. W., Stone,
F. G. A., Willkinson, G., Eds.; Pergamon Press: Oxford, UK, 1995; Vol.
12, pp 771-784. (e) Pellissier, H.; Santelli, M. Tetrahedron 2003, 59, 701-
730. (f) Wenk, H. H.; Winkler, M.; Sander, W. Angew. Chem., Int. Ed.
2003, 42, 502-528.
(2) For recent examples, see: (a) Schuster, I. I.; Craciun, L.; Ho, D. M.;
Pascal, R. A., Jr. Tetrahedron 2002, 58, 8875-8882. (b) Duong, H. M.;
Bendikov, M.; Steiger, D.; Zhang, Q.; Sonmez, G.; Yamada, J.; Wudl, F.
Org. Lett. 2003, 5, 4433-4436. (c) Lu, J.; Ho, D. M.; Vogelaar, N. J.;
Kraml, C. M.; Pascal, R. A., Jr. J. Am. Chem. Soc. 2004, 126, 11168-
11169. (d) Ikadai, J.; Yoshida, H.; Ohshita, J.; Kunai, A. Chem. Lett. 2005,
34, 56-57. (e) Hayes, M. E.; Shinokubo, H.; Danheiser, R. L. Org. Lett.
2005, 7, 3917-3920. (f) Dockendorff, C.; Sahli, S.; Olsen, M.; Milhau, L.;
Lautens, M. J. Am. Chem. Soc. 2005, 127, 15028-15029.
10.1021/ol062268m CCC: $33.50
© 2006 American Chemical Society
Published on Web 10/13/2006