Electronic effect, steric hindrance, and anchimeric assistance in oxidation of sulphides. Neighbouring-group participation through sulphur–oxygen non-bonded interaction

Abstract

Using a set of sulphides o- and p-XC₆H₄SMe, the electronic effect, steric hindrance, and anchimeric assistance for electrophilic Cl⁺ addition by TsNHCl and O-transfer by NalO₄ were investigated by a kinetic method. The steric effect and anchimeric assistance of the ortho-substituents were evaluated by comparing the reactivity of ortho- and para-substituted compounds (κ=k^o/k^p). For neighbouring-group activity the following order was obtained: CH₂OH ∼ CH₂OMe ∼ CH₂CO₂Me < CH₂CO₂H ∼ CH₂NMe₂ CH₂CO₂^–∼ CHO < CO₂Me ∼ CO₂H < COMe ∼ CONH₂ CO₂^–. Reaction rates show that the anchimeric assistance is governed by an S ⋯ O or S ⋯ N close contact developed in the transition state between oppositely polarized heteroatoms. Factors controlling neighbouring-group participation through attractive non-bonded interactions are discussed.