Neighboring Group Participation by Sulfur Involving Four-Membered-Ring Intermediates (RS-4)

摘要

The methanolysis and trifluoroethanolysis products and the methanolysis rates of a variety of chain-substituted 3-(alkylthio)-and 3-(arylthio)propyl p-toluenesulfonates, RS-C-C-C-OTs, are reported. For R = benzyl, neighboring group participation, resulting in the formation of rearranged product, and anchimeric rate acceleration have been demonstrated for all but the parent 1 degree and 2 degree 3-(benzylthio)propyl and 4-(benzylthio)-2-butyl compounds. The chain substituents promote participation as a result of a Thorpe-Ingold effect. The occurrence of anchimeric assistance without rearrangement in the 3-isopropyl and 3-tert-butyl compound has been explained on the basis of the partitioning of the thietanonium intermediate. For para-substituted 3-(arylthio)-3-(arylthio)-3-methyl-1-butyl tosylates, a Hammett sigma P deg - rho relationship has been estabilished, with rho = -1.58 for K sub delta and rho = + 0.62 for ks. Steric effects of the substituent on sulfur (R) could not be demonstrated. Rearrangement is promoted by increasing the ionic strength of the solution (by adding LiCl04) or by usign a more ionizing, less nucleophilic solvent (CF3CH20H). In the latter case, even the parent BzSCH2CH2CD2 OTs solvolyzes via a cyclic intermediate and a common intermediate is demonstrated for BzSCHMeCH2CH2OTs and BzSCH2CH2CHMeOTs.