Sequential Tandem Addition to a Tungsten–Trifluorotoluene Complex: A Versatile Method for the Preparation of Highly Functionalized Trifluoromethylated Cyclohexenes

The effects of an electron-withdrawing group on the organic chemistry of an η2-bound benzene ring are explored using the complex TpW­(NO)­(PMe3)­(η2-PhCF3). This trifluoro­toluene complex was found to undergo a highly regio- and stereo­selective 1,2-addition reaction involving protonation of an ortho carbon followed by addition of a carbon nucleo­phile. The resulting 1,3-diene complexes can undergo a second protonation and nucleo­philic addition with a range of nucleo­philes including hydrides, amines, cyanide, and protected enolates. Interestingly, the addition of the second proton and nucleo­phile occurs in a 1,4-fashion, again with a high degree of regio- and stereo­control. Oxidation of the metal allows for the isolation of highly substituted trifluoro­methyl­cyclohexenes with as many as four stereo­centers set by the metal. The ability to synthesize enantio-enriched organics was also demonstrated for a diene and a trisubstituted cyclohexene. Substitution from an enantio-enriched η2-dimethoxybenzene complex in neat trifluoro­toluene yielded enantio-enriched trifluoro­toluene complex, which was elaborated into cyclohexadienes and cyclohexenes with ee’s ranging from 92 to 99%.