P-chiral thioxophosphoranesulfenyl chlorides RR'P(S)SCL. A unique stereochemical probe to study nucleophilic displacement at a dicoordinate sulfur center

Abstract

A stereospecific synthesis of P-chiral sulfenyl chlorides 6a,b has been developed from P-chiral sulfenylamide 9a,b,c by a novel procedure employing 2Me 3SiCl + 2EtOH as the reagent of choice. The sulfenylamides 9a,b,c were prepared either by stereospecific reaction of the P-chiral hydrogen phosphinothioate 8a with aminosulfenyl halides or separation of a mixture of diastereomeric 9a,b,c by crystallisation. P-Chiral chlorides 6a,b were allowed to react with secondary amines such as morpholine or dicyclohexyl amine. All these displacement reactions proceed with almost complete stereochemical integrity at the phosphorus atom. These abservations support a synchronous mechanism of bond breaking and bond formation during nucleophilic displacement at the dicoordinate sulfur atom. The same can be said about the reaction of sulfenamides 9a,b,c with hydrogen chloride.