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

The reaction of racemic diarylmethylamines, (Ar¹Ar²CHNR₂), where Ar¹ is substituted with a 2-hydroxy group, with arylboroxines (Ar³BO)₃ in the presence of a chiral diene-rhodium catalyst gave high yields of chiral triarylmethanes (Ar¹Ar²CH*Ar³) 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.