Intermolecular Reductive Coupling of Esters with Benzophenones by Low-Valent Titanium: Synthesis of Diarylmethyl Ketones Revisited

The reductive coupling of aliphatic esters with benzophenones by Zn–TiCl₄ in THF gave two- and four-electron reduced products, diaryl­(hydroxy)­methyl ketones, and diarylmethyl ketones selectively by controlling the reaction conditions. In the reaction of aromatic esters with benzophenones, diarylmethyl ketones were obtained as the sole products. N-(Alkoxycarbonyl)-(S)-α-amino acid methyl esters gave optically active diphenylmethyl ketones by reduction with benzophenone. The obtained diphenylmethyl ketones were transformed to 4,5-cis-disubstituted oxazolidin-2-ones stereoselectively.