Conversion to sulfimides

The replacement of the oxygen atom in sulfoxides by nitrogen leads to a new class of chiral sulfur compounds, namely, sulfimides, which recently have attracted considerable attention in connection with the stereochemistry of sulfoxide-sulfimide-sulfoximide conversion reactions and with the steric course of nucleophilic substitution at sulfur. The first examples of chiral sulfimides, 88 and 89, were prepared and resolved into enantiomers by Phillips (127,128) by means of the brucine and cinchonidine salts as early as 1927. In the same way, Kresze and Wustrow (129) were able to separate the enantiomers of other structurally related sulfimides. 

The procedure most commonly used for the stereospecific preparation of optically active sulfoximides involves the reaction of optically active sulfoxides with arylsulfonyl azides in the presence of copper (98,118,131,178,179). This reaction occurs with retention of configuration at sulfur and with high stereospecificity. The stereospecific sulfoxide-sulfoximide conversion is a key reaction in the stereospecific sulfoxide-sulfimide-sulfoxiraide set of interconversions carried out by Cram and co-workers (98) and shown in Scheme 9. A similar cycle of interconversions studied independently by Andersen and co-workers (179) was used to determine the stereochemical course of the sulfoxide-sulfoximide transformation (see Scheme 10). 

The oxidative conversion of the (-)-(5 )-A-tosyl methyl-p-tolyl-sulfimide 91 to the corresponding (-)-(/ )-sulfoximide 151 is of considerable interest because the absolute configurations of the substrate and product were established by the quasi-racemate method and by X-ray analysis (98), respectively. Therefore, the stereochemical result of this experiment indicates unequivocally that oxidation of chiral tricoordinate sulfur compounds proceeds with retention of configuration. 

The cis- and frans-sulfoxides (551) and (552) have been O-methylated with Meerwein s reagent. Reaction of the methoxy derivative with MeMgBr proceeds with inversion of configuration (Scheme 211) (74JA8026). The stereochemical course of the interconversions of sulfoxide, sulfimide and sulfoximide in the 2,3-dihydrobenzo[6]thiophene series has been investigated (73JA1916). The reaction cycle (Scheme 212) involves both nucleophilic and electrophilic substitution at chiral sulfur. Inversion of configuration takes place in the conversion of (553) to (554) in pyridine. 

Scheme 10 Conversion of propargyl sulfides to N-allenylsulfenimides via [2,3]sigmatropic rearrangement of propargylic sulfimides...

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