Syn-anti Dichotomy in zinc-promoted dehalogenation of open-chain vicinal dihalides: The effect of the leaving groups

Abstract

The title effect has been investigated in the homologous series of erythro- and threo-5,6-dihalodecanes (X = Br, Y = I; X = Cl, Y = I; X = F, Y = I; X = Br, Y = Br; X = Cl, Y = Br; X = F, Y = Br; X = Cl, Y = Cl; X = F, Y = Cl). It has been found that proportion of syn-elimination in the overall reaction varies with the variation of the halogen leaving groups in the order I < Br < Cl < F, ranging between the extreme 3-30% in the erythro- and 5-60% in the threo-series. On basis of the variable transition state theory, observed pattern of syn-anti dichotomy has been correlated with the extent of double bond development in the transition state.