A highly site-, regio-, and stereoselective lewis acid catalyzed formal [3+3] cycloaddition of methylenecyclopropane-1,1-diesters with C,N-diarylnitrones

A highly site, regio, and stereoselective Lewis acid catalyzed formal [3+3] cycloaddition of methylenecyclopropane (MCP)-1,1-diesters with C,N-doarylnitrones, was conducted. It is found that the geminal installation of two electron-withdrawing groups (EWG) at the C2 position of the cyclopropane wing activates the C2-C3 bond toward cycloaddition. The results show that the formaion of a complex between the two carbonyl groups and the Lewis acid generates a discrete dipolar trimethylenemethane (TMM) transition state. The first Lewis acid is found to promote distal [3+3] cycloaddition of MCPs with 1,2-dipoles, while cycloadditions of various diarylnitrones with MCP proceed smoothly to give the 61-98% addition products. A three-component one-pot adaptation of cycloaddition using aldehyde, hydroxylamine, and MCP is found to afford 75% yield.