Highly Enantioselective Catalytic 1,3-Dipolar Cycloaddition Involving 2,3-Allenoate Dipolarophiles

A bisphosphoric acid-catalyzed 1,3-dipolar cycloaddition of buta-2,3-dienoates with azomethine ylides yields 3-methylenepyrrolidine derivatives with excellent enantioselectivity (up to 97% ee).