A study of cations generated from 1- and 3-methyl- and 1,3- and 1,7-Dimethyl-2-arylbicyclo[2,2,1]heptan-2-ols

Abstract

The ¹³C n.m.r. spectrum of the 2-(4?-methoxyphenyl)-1- methylbicyclo[2,2,1]hept-2-yl cation is reported and indicates a significant reduction in π-delocalization of charge into the aryl ring on introducing a C1-methyl group. The endo-3-methyl-2- phenylbicyclo[2,2,1]hept-2-yl cation in strong acid undergoes epimerization at C3 and does not afford the tetracyclic or dimeric compounds. 1,exo-3-Dimethyl-endo-2-phenylbicyclo[2,2,1]heptan-exo-2-ol on reaction with HSO₃F gave the exo-3,endo-6-dimethyl-2- phenylbicyclo[2,2,1]hept-2-yl cation at temperatures above -50°. This is the first alcohol containing a C1-methyl, C2-aryl system which does not undergo a WM; 6,2H; WM rearrangement. Reaction of 1,syn-7-dimethyl- endo-2-phenylbicyclo[2,2,1]heptan-exo-2-ol gave the parent 1,syn-7-  dimethyl cation which at -50° gave the exo-5,endo-6-dimethyl-2- phenylbicyclo[2,2,1]hept-2-yl cation but not the WM; 6,2H; WM product. The structural features which determine the pathway of rearrangement of these bicyclic cations are discussed.