Double-asymmetric hydrogenation strategy for the reduction of 1,1-diaryl olefins applied to an improved synthesis of CuIPhEt, a C2-symmetric N-heterocyclic carbenoid

A library of iridium and rhodium phosphine catalysts have been screened for the double-asymmetric hydrogenation of 2,6-di-(1-phenylethenyl)-4-methylaniline to produce the C2-symmetric aniline precursor of the N-heterocyclic carbenoid CuIPhEt. The best catalyst produced the desired enantiomer in 98.6% selectivity. This rare example of a highly selective hydrogenation of a 1,1-diaryl olefin enables a four-step asymmetric synthesis of the C2-symmetric phenylethyl imidazolium ion (IPhEt) from p-toluidine and phenylacetylene and its conversion to the hydrosilylation catalyst CuIPhEt.