Reactivity of vinyl sulphonic esters. Part VI. SN1-type reactivity of 1,2-diphenyl-2-phenylthiovinyl and triphenylvinyl derivatives: anchimeric assistance due to the β-sulphur atom

Abstract

The kinetic responses of trans-1,2-diphenyl-2-phenylthiovinyl sulphonates (I) and of the analogous triphenylvinyl derivatives (II) in S_N1 processes are directly compared and anchimeric assistance effects in the case of the former esters are evaluated. Rate factors, k_(I)/k_(II), ranging between 16 and 33 are observed in a variety of conditions and estimated as the lower limits of rate enhancements due to β-sulphur anchimeric assistance. The rather small kinetic effect due to β-sulphur assistance in, as well as the absence of β-aryl assistance from, S_N1-type reactions of derivatives (I) and (II) are probably due to the ‘levelling’ effect of the α-aryl residue but other factors, such as the inherent difficulty of an intramolecular nucleophilic attack in the plane of the ethylenic system, may be involved.