Thiono-Thiolo Rearrangement and Solvolysis of the Secondary Alkyl Phosphorothionates. 3

Article abstract of DOI:10.1021/jo00321a018

The protic acid catalyzed thiono-thiolo (O->S) migration of secondary alkyl groups in trialkyl phosphorothionates 1 occurs in a complex fashion.Analysis of product distribution, stereochemistry, and deuterium incorporation experiments supports an ion-pair-type intermediate, 7, as being responsible for the entire process.Nucleophilic attack by 1 on 7 initiates the chain reaction leading to 2.In trifluoroacetic acid medium inversion of configuration (96percent) at the carbon atom of the migration sec-butyl group was observed.A high concentration of 1 promotes this mode of rearrangement.However, the overall stereospecificity of sec-butyl migration is much lower due to an elimination process leading to the dialkyl hydrogen phosphorothioate 3 and an intermediate olefin which after protonation in acidic medium returns to the ion pair 7.The latter process is responsible for the nonstereospecific formation of part of the rearrangement product 2 and contributes to the lower stereospecificity of the trifluoroacetolysis process.The role of reaction-medium acidity is discussed.