Structure, Stereochemistry, and Mechanism of Formation Ofn-Acylsulfilimines

The methods for the preparation of sulfilimines are summarized, and the stereochemistry and electronic structure of N-acylsulfilmines are discussed. Sulfilimines have a non-planar structure, but the SIV[sbnd]N bond character cannot be determined from their resolvability. N-Sulfonylsulfilimines (RR'SNSO2Q) contain a delocalized SIVNSVI d bond system, the SIVN and SVIn bonds are of intermediate bond order. SIV[sbnd]CH3 hyperconjugation causes strong bond shortening. An asymmetric conformation of a sulfilimine containing two identical SIV substituents was found in the crystalline state which could be accounted for theoretically. The rotation of the SN bond is not restricted in solution. The structure of N-carboacylsulfilimines (RR'SNCOQ) is strongly polar due to the strong NCO conjugation, and the instability of these compounds can be ascribed to the polar structure. The reaction between thioethers and chloramine-T is a nucleophilic substitution; the rate of the reaction is influenced by the nucleophilic character of the thioether sulfur atom. Thioether carboxylic acids are usually oxidized by chloramine-T and only give a sulfilimine if the carboxyl group is fixed sufficiently distant from the sulfur atom. The formation of sulfilimines from an optically active sulfoxide by the action of a sulfonamide (or N-sulfinylsulfonamide) proceeds via a trigonal bipyramidal intermediate with complete inversion. The intermediate of the sulfilimine synthesis starting from arylsulfonyl azides is a sulfonyl imene.