Solvolytic rearrangement studies with 14C or 13C labeled (E)- and (Z)-1,2-diphenyl-2-tolylvinyl bromides

The reaction of (E)-, (Z)-, or a 2:3 mixture of (E)- and (Z)-1,2-diphenyl-2-tolyl[2-14C]vinyl bromide ((E)-, (Z)-, or (E,Z)-3-Br-2-14C) in HOAc–AgOAc gave a 1:1 mixture of the structurally unrearranged but isotopically scrambled (E)- and (Z)-1,2-diphenyl-2-tolyl[1,2-14C]vinyl acetates ((E,Z)-3-OAc-1,2-14C), with an average of 18.3% scrambling of the 14C label from C-2 to C-1 arising from 1,2-tolyl shifts in the 1,2-diphenyl-2-tolylvinyl cation (3). No detectable amount of the structurally rearranged 2,2-diphenyl-1-tolylvinyl acetate (4-OAc) was formed. Solvolysis of (E,Z)-3-Br-2-14C in TFE-2,6-lutidine gave as products 62% 4-OTFE-1,2-14C and 38% of a 1:1 mixture of (E)- and (Z)-3-OTFE-1,214C. Only (Z)-3-OTFE-1,2-14C could be isolated as a pure product and it showed an average of 44.7% scrambling of the label from C-2 to C-1. Similar trifluoroethanolyses of (E,Z)-3-Br-2-13C coupled with gas chromatographic - mass spectral analyses of the diphenyl and phenyl tolyl ketones from ozonolysis of the product mixture showed 44.6% scrambling in the (E,Z)-3-OTFE-1,2-13C, confirming the 14C results for the (Z) isomer. Nondegenerate rearrangements from 1,2-phenyl shifts before and after the degenerate 1,2-tolyl shifts to give 4-OTFE-1-13C and 4-OTFE-2-13C were also observed, demonstrating the occurrence of successive 1,2-aryl shifts in these triarylvinyl cations.