Highly Regio- and Stereoselective Synthesis of
Indene and Benzo[b]furan Derivatives via a
Pd-Catalyzed Carboannulation of Propargyl
Carbonates with Nucleophiles
Hai-Peng Bi,† Li-Na Guo,† Fa-Rong Gou,† Xin-Hua Duan,†
Xue-Yuan Liu,† and Yong-Min Liang*,†,‡
State Key Laboratory of Applied Organic Chemistry,
Lanzhou UniVersity, and State Key Laboratory of Solid
Lubrication, Lanzhou Institute of Chemical Physics,
Chinese Academy of Science,
Lanzhou 730000, People’s Republic of China
ReceiVed February 3, 2008
FIGURE 1. Palladium-catalyzed double addition of nucleophiles to
propargylic substrates.
intramolecular nucleophilic attack is prior to the intermolecular
reaction. In 2003, Yoshida et al. accomplished the cyclization
of 4-methoxycarbonyloxy-2-butyn-1-ols, but dihydrofuran and
epoxide were formed as the side products via a prior intermo-
lecular reaction (Figure 1c).5
A new and efficient synthesis of indene and benzo[b]furan
derivatives has been achieved via Pd-catalyzed carboannu-
lation of propargyl carbonates with nucleophiles in good to
excellent yields with high regio- and stereoselectivity. A
novel sequence of nucleophilic attack is observed, and a
possible mechanism is proposed.
Very recently, we have developed methods for the synthesis
of indene derivatives by carboannulation.4,6 Encouraged by
reported results,7 we herein report a novel Pd-catalyzed cy-
clization of propargyl carbonates with phenol nucleophiles for
the synthesis of indene derivatives with high regioselectivity.
In this process, intermolecular nucleophilic attack happened prior
to intramolecular reaction (Scheme 1).
SCHEME 1
The formation of carbon-carbon and carbon-heteroatom
bonds via Pd-catalyzed reactions of propargyl compounds with
nucleophiles has attracted much interest in the past a few
decades.1 The key step in these reactions is the formation of an
allenyl- or π-propargylpalladium complex (an equilibrium
process) by facile decarboxylation, which undergoes double
nucleophilic attack to form products. Recently, Yoshida2 and
Cacchi3 et al. reported Pd-catalyzed reactions of propargyl
carbonates with nucleophiles for the synthesis of substituted 2,3-
dihydrofurans, benzofurans, and functionalized indoles (Figure
1a). Very recently, we also reported a convenient method for
the preparation of indene derivatives via a regioselective
nucleophilic attack at different sites of propargyl carbonates
catalyzed by palladium (Figure 1b).4 In these processes,
Initially, we started our investigation of the reaction by using
1.0 equiv of propargyl carbonate (1a; 0.2 mmol) and 1.2 equiv
of phenol (2a) in the presence of 5 mol % of Pd2(dba)3 and 20
mol % dppf in THF under argon at 55 °C for 3 h; the desired
(4) (a) Duan, X.-H.; Guo, L.-N.; Bi, H.-P.; Liu, X.-Y.; Liang, Y.-M. Org.
Lett. 2006, 8, 5777. (b) Guo, L.-N.; Duan, X.-H.; Bi, H.-P.; Liu, X.-Y.; Liang,
Y.-M. J. Org. Chem. 2007, 72, 1538.
(5) (a) Yoshida, M.; Fujita, M.; Ishii, T.; Ihara, M. J. Am. Chem. Soc. 2003,
125, 4874. (b) Yoshida, M.; Ihara, M. Angew. Chem., Int. Ed. 2001, 40, 616.
(6) (a) Guo, L.-N.; Duan, X.-H.; Bi, H.-P.; Liu, X.-Y.; Liang, Y.-M. J. Org.
Chem. 2006, 71, 3325. (b) Duan, X.-H.; Guo, L.-N.; Bi, H.-P.; Liu, X.-Y.; Liang,
Y.-M. Org. Lett. 2006, 8, 3053. (c) Bi, H.-P.; Guo, L.-N.; Duan, X.-H.; Gou,
F.-R.; Huang, S.-H.; Liu, X.-Y.; Liang, Y.-M. Org. Lett. 2007, 9, 397. (d) Bi,
H.-P.; Liu, X.-Y.; Gou, F.-R.; Guo, L.-N.; Duan, X.-H.; Liang, Y.-M. Org. Lett.
2007, 9, 3527. (e) Bi, H.-P.; Liu, X.-Y.; Gou, F.-R.; Guo, L.-N.; Duan, X.-H.;
Shu, X.-Z.; Liang, Y.-M. Angew. Chem., Int. Ed. 2007, 46, 7068. (f) Guo, L.-
N.; Duan, X.-H.; Liu, X.-Y.; Hu, J.; Bi, H.-P.; Liang, Y.-M. Org. Lett. 2007, 9,
5425.
† State Key Laboratory of Applied Organic Chemistry, Lanzhou University.
‡ State Key Laboratory of Solid Lubrication, Lanzhou Institute of Chemical
Physics, Chinese Academy of Science.
(1) For reviews of Pd-catalyzed reactions of propargyl carbonates see: (a)
De Meijere, A., Diederich, F. Eds. Metal-Catalyzed Cross-Coupling Reactions;
Chapter 10; Wiley-VCH: New York, 2004. (b) Tsuji, J. Acc. Chem. Res. 1969,
2, 144. (c) Tsuji, J.; Minami, I. Acc. Chem. Res. 1987, 20, 140. (d) Tsuji, J.
Tetrahedron 1986, 42, 4361. (e) Tsuji, J.; Mandai, T. Angew. Chem., Int. Ed.
Engl. 1995, 34, 2589.
(7) The π-propargylpalladium complex is formed in a more stable manner
in the presence of a bidentate ligand than in the presence of a monodentate
ligand, see: (a) Tsutsumi, K.; Ogoshi, S.; Nishiguchi, S.; Kurosawa, H. J. Am.
Chem. Soc. 1998, 120, 1938. (b) Tsutsumi, K.; Kawase, T.; Kakiuchi, K.; Ogoshi,
S.; Okada, Y.; Kurosawa, H. Bull. Chem. Soc. Jpn. 1999, 72, 2687.
(2) (a) Yoshida, M.; Morishita, Y.; Fujita, M.; Ihara, M. Tetrahedron Lett.
2004, 45, 1861. (b) Yoshida, M.; Morishita, Y.; Fujita, M.; Ihara, M. Tetrahedron
2005, 61, 4381.
(3) Ambrogio, I.; Cacchi, S.; Fabrizi, G. Org. Lett. 2006, 8, 2083.
10.1021/jo8002776 CCC: $40.75
Published on Web 05/22/2008
2008 American Chemical Society
J. Org. Chem. 2008, 73, 4713–4716 4713