Synlett 2007(12): 1913-1916  
DOI: 10.1055/s-2007-984531
LETTER
© Georg Thieme Verlag Stuttgart · New York

Homocoupling of Arylboronic Acids with a Catalyst System Consisting of a Palladium(II) N-Heterocyclic Carbene Complex and p-Benzoquinone

Yoshihiko Yamamoto*
Department of Applied Chemistry, Graduate School of Science and Engineering, Tokyo Institute of Technology, O-okayama, Meguro-ku, Tokyo 152-8552, Japan
Fax: +81(3)57343339; e-Mail: omyy@apc.titech.ac.jp;
Further Information

Publication History

Received 12 April 2007
Publication Date:
27 June 2007 (online)

Abstract

In the presence of 1-3 mol% SIPr-ligated Pd(OAc)2 and 0.6 equivalent of p-benzoquinone, various arylboronic acids underwent homocoupling in MeOH at ambient temperature to produce symmetrical biaryls in 38-96% yields.

17

Typical Procedure - Synthesis of 3a
To a solution of p-tolylboronic acid 2a (69.8 mg, 0.502 mmol) and p-benzoquinone (33.2 mg, 0.307 mmol) in MeOH (10 mL) was added 1a (3.25 mg, 0.0051 mmol), and the flask was evacuated and backfilled with Ar three times at -78 °C. The reaction mixture was stirred for 24 h at r.t. under Ar. The solvent was removed in vacuo and the residue was purified by silica gel column flash chromatography (eluent: hexane) to afford 3a (40.2 mg, 88%) as colorless solids. Other reactions were also carried out in a similar manner. If the product and excess pbq are inseparable by chromatog-raphy, crude materials were treated with excess NaBH4 in MeOH at r.t. prior to purification. All starting materials and products are known compounds.