Organocatalytic Enantioselective Construction of Chiral Tetraarylmethanes from 4-(2-Hydroxyphenyl)benzyl Alcohols.

Organocatalytic enantioselective construction of chiral tetraarylmethanes has been achieved via the formal substitution of 4-(2-hydroxyphenyl)benzyl alcohols. With the aid of chiral phosphoric acid, 2,4'-biphenyl quinone methides were formed in situ from α-functionalized alcohols, followed by stereoselective 1,8-addition of 2-arylpyrroles to give the target tetraarylmethanes in 72-96% yields with 75-95% ee. Density functional theory calculations elucidate the reaction mechanism, both revealing the origin of enantioselectivity and identifying the rate-determining step. Significantly, this work establishes the 4-(2-hydroxyphenyl)phenyl unit as an effective auxiliary group that enables the corresponding α-functionalized alcohols to participate in the organocatalytic asymmetric construction of enantioenriched tetraarylmethanes.