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■ Synthesis of Benzofurans from Isovanillin via C-Propenylation-O-Vinylation and Ring-closing Metathesis

Tzu-Wei Tsai, Eng-Chi Wang,* Keng-Shiang Huang, Sie-Rong Li, You-Feng Wang, Yu-Li Lin, and Yung-Hua Chen

*Faculty of Medicinal and Applied Chemistry, Kaohsiung Medical University, Kaohsiung City 807, Taiwan, R.O.C.

Abstract

Substituted benzofurans derived from isovanillin were synthesized. 2-Allyl-3-alkoxy-4-methoxyphenol, prepared from isovanillin via the Claisen rearrangement, O-alkylation and Baeyer-Villiger oxidation, were chloroethylated by two-phase reaction to furnish 1-allyl-3-alkoxy-(2-chloroethoxy)-4-methoxybenzenes. The given compounds were treated with potassium tert-butoxide to undergo the isomerization of O-allyl group and dehydrochlorination of 2-chloroethoxy group to efficiently construct the precursors with C-propenyl- O-vinyl function for the ring-closing metathesis (RCM) in one pot. Then, then precursors were subjected to RCM to furnish 4,5-O-difunctionalized benzofurans in good over-all yield, respectively.