Asymmetric Diels–Alder Reaction Involving Dynamic Enantioselective Crystallization

Asymmetric Diels–Alder reaction was achieved under achiral conditions. Reaction of prochiral 2-methylfuran and N-phenylmaleimide in heptane or hexane solution at 80 °C efficiently gave a conglomerate crystal of exo-type Diels–Alder adduct selectively, and continuous suspension of the reaction mixture with glass beads promoted attrition-enhanced deracemization, leading to an optically active exo-adduct in 90% ee.