3 years ago

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

Sequential Tandem Addition to a Tungsten–Trifluorotoluene Complex: A Versatile Method for the Preparation of Highly Functionalized Trifluoromethylated Cyclohexenes
Hannah S. Nedzbala, W. Dean Harman, Logan A. Combee, Michal Sabat, Jeffery T. Myers, Katy B. Wilson
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%.

Publisher URL: http://dx.doi.org/10.1021/jacs.7b05118

DOI: 10.1021/jacs.7b05118

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