Synthesis Of 2-Substituted 7-Hydroxybenzofuran-4-Carboxylates Via Addition Of Silyl Enol Ethers To O-Benzoquinone Esters

Mukaiyama Michael addition of silyl enol ethers 13 to the 1,2-quinone-4-carboxylate 6 (formed in situ by oxidation of the catechol ester 8) afforded the 2-subshuted 7-hydroxybenzofuran-4-carboxylates 14 in fair to good yields. Alkyl and aryl systems work well, but highly electron-rich silyl enol ethers could not be used because of competing oxidation.