Thermal Reactions of Substituted Cyclopropenone Acetals. Regio-and Stereochemistry of Vinylcarbene Formation and Low-Temperature [3 + 2] Cycloaddition

Cyclopropenone acetals bearing olefinic substituents of diverse electronic character have been synthesized and examined for their thermal behavior toward water and electron-deficient olefins. The substituted cyclopropenes underwent regio-and stereoselective hydration to give acrylate derivatives via vinylcarbene species, providing new data on the regio-and stereochemistry of vinylcarbene species. They also underwent regioselective [3 + 2] cycloadditions to electron-deficient olefins to give a variety of cyclopentenone acetals. In particular, phenylthio and ester substituents connected to the cyclopropene carbon effected highly regioselective vinylcarbene formation below room temperature to permit the thermal [3 + 2] cycloaddition to take place under extremely mild conditions.