Stereochemical Effects in the Gas-Phase Pinacol Rearrangement of cis- and trans-1,2-Dimethylcyclopentane-1,2-diol

Article abstract of DOI:10.1021/ja00284a009

The pinacol rearrangement of cis- and trans-1,2-dimethylcyclopentane-1,2-diol, promoted by the gaseous Broensted acids D3⁺, CH5⁺/C2H5⁺, and t-C4H9⁺, was studied by mass spectrometric and radiolytic methods.Dehydration of the protonated substrate is rate limiting, and competitive experiments with pinacol, carried out at high pressure (760 torr), showed that the cis rearranges more rapidly than the trans isomer, indicating participation of the migrating methyl group to the leaving water molecule.The results are compared with those concerning the same substrates in solution, where no evidence of anchimeric assistance was found.