Asymmetric Synthesis of Triarylmethanes by Rhodium-Catalyzed Enantioselective Arylation of Diarylmethylamines with Arylboroxines

The reaction of racemic diarylmethylamines, ((ArArCHNR2)-Ar-1-C-1), where Ar-1 is substituted with a 2-hydroxy group, with arylboroxines ((ArBO)-B-3)(3) in the presence of a chiral diene-rhodium catalyst gave high yields of chiral triarylmethanes ((ArArCH)-Ar-1-C-2*Ar-3) with high enantioselectivity (up to 97% ee). The reaction is assumed to proceed through o-quinone methide intermediates which undergo Rh-catalyzed asymmetric 1,4-addition of the arylboron reagents.