Abstract
β‐Sultams, biologically interesting sulfonyl analogues of β‐lactams, have been prepared by an organocatalytic asymmetric formal [2+2]‐cycloaddition approach of non‐nucleophilic imines with alkyl sulfonyl chlorides. In the case of very electron poor N‐tosyl imines derived from chloral or ethylglyoxylate, this reaction type was catalyzed by cinchona alkaloids providing the heterocycles in high yield, with good diastereoselectivity and up to 94 % ee. Mechanistic investigations suggested that the product formation proceeded via a zwitterionic imine–catalyst adduct. The scope was significantly extended by 2‐pyridylsulfonyl imines derived from non‐activated aromatic aldehydes employing Yb(OTf)~3~ as Lewis acid cocatalyst. The synthetic value of the strained enantioenriched β‐sultams was demonstrated by smooth nucleophilic ring opening reactions with O‐, N‐ and C‐nucleophiles yielding a variety of acyclic β‐aminosulfonyl (taurine) derivatives (sulfonates, sulfonamides, sulfones) without racemization or epimerization.