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The presence of different amounts of added LiClO4in the solvolysis of triphenyl[2-14C]vinyl bromide (1-Br-2-14C) or trianisyl[2-14C]vinyl bromide (2-Br-2-14C) in 70% HOAc did not materially affect the extent of scrambling of the label arising from 1,2-aryl shifts in the triarylvinyl cation or kr, the rate constant for the 1,2-aryl shift. Solvolysis of a 2:3 mixture of (E)- and (Z)-1,2-diphenyl-2-tolylvinyl bromide ((E,Z)-3-Br) in 70% HOAc gave an 85:15 mixture of 1,2-diphenyl-2-tolylethanone (5) and 2,2-diphenyl-1-tolylethanone (6), the latter product, 6, being derived from a 1,2-phenyl shift in the 1,2-diphenyl-2-tolylvinyl cation to the more stable 2,2-diphenyl-1-tolylvinyl cation. With (E,Z)-3-Br-2-13C as substrate and analysis by gc–ms, about 26–27% scrambling of the 13C label was found in both products, 5-1,2-13C and 6-1,2-13C. Solvolyses of (E,Z)-3-Br-2-13C in 50% and 70% HOAc showed that the extent of scrambling in the major products, 5-1,2-13C, was lower in 50% HOAc than in 70% HOAc, similar to a trend previously observed for solvolyses of 1-Br-2-14C. In contrast, solvolyses of 2-Br-2-14C in 50, 70, or 90% HOAc gave essentially the same extent of scrambling. Mechanistic implications of these results are discussed.

Solvolyses were carried out with 6.0 mMdoubly labeled 1,2-dianisyl-2-p-(2H3)methoxyphenyl[2-13C]vinyl bromide in 70% HOAc – 30% H2O in the presence of 0, 1, 5, 10, or 400 molar equivalents of added NaOAc. The distributions of products derived from the 4 possible isotopomeric trianisylvinyl cationic intermediates were determined from the mass spectra of the isotopomeric dianisyl ketones obtained from degradation of the reaction products, the spectra being obtained by the chemical ionization technique in order to minimize possible complications by multiple fragmentations. The mass spectrometrie results obtained showed agreement with previously obtained 14C scrambling data and with the 13C scramblings obtained in the present study using 13C nmr. Increasing amounts of added NaOAc had the effect of decreasing the extents of scrambling from 1,2-anisyl shifts as previously observed. However, the formation of products from all 4 possible doubly labeled isotopomeric trianisylvinyl cations definitely demonstrated the occurrence of successive 1,2-anisyl shifts in the trianisylvinyl cation, and the detection of such successive shifts was not possible in previous work using a singly labeled substrate. The observed distribution of products derived from the 4 isotopomeric cations could be calculated assuming various contributions from equilibrations among these isotopomeric cations, and the mechanistic implications of the results are discussed.

The acetolysis of trans-1,2-diphenyl-2-phenylthiol[1-13C]vinyl tosylate (2-OTs-1-13C) under anhydrous conditions (HOAc–Ac2O–NaOAc) gave trans-1,2-diphenyl-2-phenylthio[1,2-13C]vinyl acetate (2-OAc-1,2-13C) as product. The label was scrambled equally over C-1 and C-2 and there was no detectable amount of cis-product. These results are consistent with the involvement of an intermediate sulfur-bridged thiirenium ion in the reaction. Soivolysis of 2-OTs-1-13C in 70% HOAc – 30% H2O containing 3 equiv. of NaOAc gave 1,2-diphenyl-2-phenylthio[1,2-13C]ethanone (α-phenyl-α-(phenylthio)acetophenone) (5-1,2-13C) and 1,2-diphenyl[1,2-13C]ethanone (desoxybenzoin) (6-1,2-13C) as major and minor products, respectively. The 13C-label in both of these ketones was again equally distributed over C-1 and C-2. Further studies with unlabeled 2-OTs showed that its soivolysis in aqueous HOAc gave, besides ketones 5and 6, some benzil and diphenyl disulfide. It was also found that 6, benzil, and diphenyl disulfide were derived from the initial product 5. A possible mechanism for these conversions is proposed.