Neighboring Group Participation by Oxygen in the Solvolysis of Acyclic Gamma-Alkoxy Substituted p-Toluenesulfonates

摘要

Methanolysis of branched 3-(benzyloxy)propyl p-toluenesulfonates, PhCH2OCR1R2CR3R4CHR5OTs (R1 = Me, R2-R5 = H; R1 = R2 = Me, R3-R5 = H; R1 = R2 = R5 = Me; R3 = R4 = H; R1 = R2 = R4 = R5 = H, R3 = Me; R1 = R2 = R5 = H, R3 = R4 = Me) proceeds with partial rearrangement, implying neighboring group participation, only when there are geminal methyl groups in the 2- or 3-position (R33 = R4 = Me or R1 = R2 = Me). Addition of lithium perchlorate enhances the extent of rearrangement. No or negligible anchimeric assistance is manifest either in the absence or in the presence of the salt. Participation thus seems to occur past the transition state. The primary 3-substituted alcohol precursors of the p-toluenesulfonates are synthesized by solvomercuration-borohydride reaction of alpha, Beta-unsaturated acids followed by reduction with lithium aluminum hydride or diborane; the corresponding secondary alcohol is similarly obtained from 4-methyl-3-penten-2-ol, (CH3)2C-CHCHOHCH3 double bond, by solvomercuration-borohydride reduction. (Author)