Distinctive Meta-Directing Group Effect for Iridium-Catalyzed 1,1-Diarylalkene Enantioselective Hydrogenation
摘要:
An iridium-catalyzed asymmetric hydrogenation of 1,1-diarylkenes is described. Employing a novel, modular phosphoramidite ligand, PhosPrOx, in this transformation affords biologically relevant 1,1-diarylmethine products in good enantiomeric ratios (96.5:3.5 to 71:29). We propose that a meta-directing group, 3,5-dimethoxyphenyl, is responsible for the observed enantioselection, the highest reported, to date, for iridium-catalyzed hydrogenation of 1,1-diarylalkenes lacking ortho-directing groups.
Traceless Directing Group for Stereospecific Nickel-Catalyzed Alkyl−Alkyl Cross-Coupling Reactions
作者:Margaret A. Greene、Ivelina M. Yonova、Florence J. Williams、Elizabeth R. Jarvo
DOI:10.1021/ol300891k
日期:2012.8.17
Stereospecific nickel-catalyzed cross-couplingreactions of benzylic 2-methoxyethyl ethers are reported for the preparation of enantioenriched 1,1-diarylethanes. The 2-methoxyethyl ether serves as a traceless directing group that accelerates cross-coupling. Chelation of magnesium ions is proposed to activate the benzylic C–O bond for oxidative addition.