Organocatalytic Enantioselective Synthesis of [5.7]-Fused ε-Sultam N,O-Heterocycles via (3+2)-Annulation of Seven-Membered Cyclic N-Sulfonylimines with γ-Hydroxy-α,β-Unsaturated Ketones

A highly stereoselective protocol for the (3 + 2)-annulation of biphenyl-bridged seven-membered cyclic N-sulfonylimines with gamma-hydroxy-alpha,beta-unsaturated ketones was developed. The reactions afforded a wide range of chiral [5.7]-fused epsilon-sultams bearing N-adjacent 1,3-stereocenters in excellent yields (93-98% yields) and high enantio/diastereoselectivities (up to >99% ee, >20:1 d.r.) and two other examples with alkoxyl groups were obtained in 52-61% yields, 95% ee, and >20:1 d.r. by utilizing organocatalysis with quinine-derived squaramides.