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■ A Convenient Two-Step Synthesis of 7-Aryl-6,7-dihydrothieno[2,3-b]pyrazines from Aryl(3-chloropyrazin-2-yl)methanones

Kazuhiro Kobayashi,* Teruhiko Suzuki, and Naoki Matsumoto

*Division of Applied Chemistry, Department of Chemistry and Biotechnology, Graduate School of Engineering, Tottori University, 4-101 Koyama-minami, Tottori 680-8552, Japan

Abstract

An efficient method for the preparation of 7-aryl-6,7-dihydrothieno[2,3-b]pyrazines (3) under mild conditions has been developed. The reaction of aryl(3-chloropyrazin-2-yl)methanones (1), derived from commercially available 2-chloropyrazine, with methylenetriphenylphosphorane in THF at room temperature gave the corresponding 2-(1-arylethenyl)-3-chloropyrazines (2), which were treated with NaSH·nH2O in DMF at room temperature to lead to the desired products (3) in acceptable yields. These products are dehydrogenated with air in refluxing toluene in the presence of a catalytic amount of Pd/C to yield the corresponding 7-arylthieno[2,3-b]pyrazines (4).