Highly Efficient and Diastereoselective Construction of Tricyclic Pyrrolidine‐Fused Benzo[b]thiophene 1,1‐dioxide Derivatives via 1,3‐Dipolar [3 + 2] Cycloaddition

A rapid and highly efficient 1,3‐dipolar 3 + 2] cycloaddition of nonstabilized azomethine ylides generated in situ with benzob]thiophene 1,1‐dioxides as the dipolarophiles has been developed. The efficient method affords tricyclic pyrrolidine‐fused benzob]thiophene 1,1‐dioxide derivatives in high to excellent yields (up to 99%) with excellent diastereoselectivities (up to >25:1 dr) under mild reaction conditions. The structure of a typical product was confirmed by X‐ray crystallography.