Alkylation of 4H,6H-thieno[3,4-c]furan 5,5-dioxide and its use as a 3,4-dimethylenefuran synthon in intramolecular Diels–Alder reaction

Abstract

Alkylation of 4H,6H-thieno[3,4-c]furan 5,5-dioxide (furan-annulated sulfolene)1 readily gave its 4-alkyl, 4,6-dialkyl, or 4,4-dialkyl derivatives, selectively. Attempts were made to use the appropriate derivatives as 3,4-dimethylenefuran synthons in intramolecular Diels–Alder reactions. Thus when they were heated after treatment with methyl vinyl ketone, a Diels–Alder reaction with methyl vinyl ketone on the furan moiety, desulfonylation, intramolecular Diels–Alder reaction of the resulting dienes, and retro Diels–Alder reaction occurred sequentially to afford the tricyclic fused furans 17a–c; in good yields.