Asymmetric cycloaddition of anthrone and maleimides catalyzed by C2-chiral pyrrolidines

Abstract

Catalytic asymmetric cycloaddition of anthrone with N-alkyl- and N-arylmaleimides with various substituents in the aromatic ring was carried out in the presence of C₂-chiral pyrrolidines to afford chiral, non-racemic [4 + 2] adducts. Among them, good catalytic activity was observed with the pyrrolidines with a N-(4-pyridyl)methyl group 1h, which was discussed from the viewpoint of conformational analysis. The best stereoselectivity of 87% ee was attained when the reaction of N-(2-tert-butylphenyl)maleimide 4j and anthrone was promoted with 1h.