Some isotopic scrambling studies with singly or doubly labeled triphenylvinyl bromide

Abstract

The solvolysis of triphenyl[2-14C]vinyl bromide (1-Br-2-14C) in 70% HOAc – 30% H2O or in 2,2,2-trifluoroethanol (TFE) carried out in the presence of an excess of p-CH3C6H4SNa gave the triphenylvinyl p-tolyl thioether (1-STol) with a greatly decreased extent of scrambling of the 14C-label from C-2 to C-1 when compared with analogous reactions without the presence of the p-toluenethiolate anion. For example, the 1-STol product from the reaction of 1-Br-2-14C in 70% HOAc – p-CH3C6H4SNa showed only 0.5–0.9% scrambling, while previous studies on the reaction of 1-Br-2-14C in 70% HOAc – NaOAc gave 14.7 ± 0.7% scrambling. Previous work on the solvolysis of 1,2-diphenyl-2-[2H5]phenyl[2-13C]vinyl bromide (1-Br-2-13C-2-Ph-d5 in 70% HOAc, as well as the present results from the solvolysis of 1-Br-2-13C-2-Ph-d5 in TFE – 2,6-lutidine, gave products derived from all 4 possible isotopomeric triphenylvinyi cations 3, 4, 5, and 6 arising from successive 1,2-phenyl shifts. On the other hand, solvolysis of 1-Br-2-13C-2-Ph-d5 in 70% HOAc or TFE containing an excess of p-CH3C6H4SNa gave 1-STol in which the isotopically rearranged product was derived only from ion 5 arising from a 1,2-shift of the unlabeled phenyl group with no detectable amount of production derived from a 1,2-shift of the perdeuterophenyl group. These results are interpreted by the rapid trapping of the triphenylvinyi cation by the highly nucleophilic p-toluenethiolate anion.