Kinetic study of substituent effects on the mechanism of β-elimination of arenethiol from trans-2,3-bis(arylthio)-4-nitro-2,3-dihydrothiophenes in toluene

Abstract

The 2,3-dihydrothiophene derivatives (1b–f) readily undergo, in toluene, regiospecific tributylamine-promoted syn-elimination of arenethiol to give the 2-(arylthio)-4-nitrothiophenes (2b–f). For the rather complex kinetic behaviour displayed by each member of the series, a rationalisation is proposed based on a stability of the substrate's conjugate base sufficient to allow formation of non-negligible concentrations of an intermediate ion pair along the reaction co-ordinate. The system allows direct conclusions to be drawn concerning the leaving-group expulsion step: an advanced extent of bond cleavage between carbon and the leaving group can be postulated in the transition state.