Diels–Alder reactions of ( RS)-3-[(1 S)-isoborneol-10-sulfinyl]-1-methoxybuta-1,3-dienes with electron-deficient carbodienophiles. The effects of Lewis acid catalysis

Abstract

Uncatalyzed cycloadditions of ( R S,E)- 1 and ( R S,Z)-3-[(1 S)-isoborneol-10-sulfinyl]-1-methoxybuta-1,3-diene 2 with maleimide and N-phenylmaleimide occurred with complete endo and very high facial diastereoselectivities. The effects of Lewis acid catalysis on these Diels–Alder reactions have been evaluated. LiClO 4 catalyzed cycloaddition of 1 with dimethyl maleate gave cyclohexene 13 as the unique product with complete control of endo and π-facial diastereoselectivities exerted by the sulfinyl group. A significant improvement in diastereoselectivity was also observed in the LiClO 4 catalyzed cycloaddition of 1 with dimethyl fumarate.