Phosphine-Catalyzed Enantioselective [2+4] Cycloaddition to Synthesize Pyrrolidin-2-one Fused Dihydropyrans Using α‑Substituted Allenoates as C2 Synthons

A bifunctional phosphine-catalyzed highly enantioselective [2+4] cycloaddition of α-substituted allenoates with (E)-1-benzyl-4-olefinicpyrrolidine-2,3-diones has been achieved, giving pyrrolidin-2-one fused dihydropyran derivatives in moderate to good yields with excellent enantioselectivities (up to 98% ee). This reaction provides a useful catalytic asymmetric access to dihydropyran structural motifs.