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

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.