Racemic 6-ethenyl-7-oxabicyclo[2.2.l]hept-5-en-2-one (23), 5-ethenyl-7-oxabicyclo[2.2.1]hept-5-en-2-one (25) and their ethylene acetals 24 and 26, respectively, were derived from the Diels-Alder adduct of furan to 1-cyanovinyl acetate (27). The Diels-Alder additions of 26 to dimethyl acetylenedicarboxylate, to methyl propynoate, to N-phenylmaleimide, and to methyl acrylate were highly exo-face selective, as were the cycloadditions of methyl propynoate to dienones 23 and 25 and of dimethyl acetylenedicarboxylate to ethylenedioxy-diene 24. The cheletropic additions of SO2 to 23-26 gave exclusively the corresponding sulfolenes 57-60 resulting from the exo-face attack of the semicyclic dienes under conditions of kinetic and thermodynamic control.