Unimolecular Solvolyses in Ionic Liquid: Alcohol Dual Solvent Systems.

A study was undertaken of the solvolysis of pivaloyl triflate in a variety of ionic liquid:alcohol solvent mixtures. The solvolysis is a kΔ process (i.e.

Gamma-silyl cyclobutyl carbocations.

A series of 3-trimethylsilyl-1-substituted cyclobutyl trifluoroacetates have been prepared and reacted in CD(3)CO(2)D. Rate data indicate that the substrates with the trimethylsilyl group cis to the leaving group react with assistance due to gamma-silyl participation. Rate enhancements range from a factor of 209 for alpha-phenyl-substituted cations to 4.

Systematic repression of beta-silyl carbocation stabilization.

Solvolysis of 1-(trimethylsilylmethyl)cyclopropyl mesylate in CD(3)CO(2)D gives ring-opened products as well as methylenecyclopropane. The rate enhancement due to the beta-trimethylsilyl group is a factor of about 10(6). The large stabilizing effect of a beta-silyl group (which can cause rate enhancements of up to 10(12)) on the intermediate cation has been repressed.