SYNTHESIS AND REACTIONS OF ACHIRAL 3-SUBSTITUTED VINYLKETENE ACETALS AS DIENES IN THE DIELS-ALDER REACTION

The synthesis of three new vinylketene acetals, each bearing a heteroa tom substituent at C3 of the diene unit, and their reactions with repr esentative dienophiles in Diels-Alder reactions are presented. All the dienes react well at room temperature, indicating substantial activat ion of the cycloaddition event. The stereochemistry of the major Diels -Alder product of a 3-SPh-substituted vinylketene acetal is opposite t o that produced by the corresponding 3-unsubstituted compound.