Diastereoselective Base-Catalyzed Formal [4 + 2] Cycloadditions of <i>N</i>‑Sulfonyl Imines and Cyclic Anhydrides

A diastereoselective base-catalyzed Mannich reaction of cyclic, enolizable anhydrides and <i>N</i>-sulfonyl imines for the synthesis of δ-lactams is reported. This anhydride Mannich reaction tolerates imines derived from aryl and enolizable aldehydes. A base-catalyzed product epimerization pathway ensures high anti diastereoselectivity in aryl and achiral enolizable imines.