A theoretical study of neighboring-group participation in thione-to-thiol rearrangement of xanthates. molecular orbital calculation using a conductor-like screening model (COSMO) approach.

The transition structures of the thione-to-thiol rearrangement of O-(2-dimethylaminoethyl and 2-methylthio-) S-methyl xanthates in several solvents were located by semiempirical molecular orbital method (PM3) using the conductor-like screening model (COSMO) approach. Each transition state transforms into the ion-pair intermediate with a three-membered ring structure (aziridinium or thiiranium), indicating that the rearrangement proceeds through an ionic intermediate with the anchimeric assistance of the neighboring group. The intermediary structures in gas phase are also analyzed by ab initio and density functional theory calculations.