A facile asymmetric transfer hydrogenation of ortho-substituted aryl N-heteroaryl ketones and non-ortho-substituted N-oxide of aryl N-heteroaryl ketones using a readily available oxo-tethered ruthenium complex as a catalyst and sodium formate as a hydrogen source in an aqueous solution has been discovered. A variety of chiral aryl N-heteroaryl methanols were obtained with up to 99.9% ee.

A highly enantioselective transfer hydrogenation of non-ortho-substituted aryl N-heteroaryl ketones, using readily available chiral diamine-derived iridium complex (S,S)-1f as a catalyst and sodium formate as a hydrogen source in a mixture of HO/i-PrOH (v/v = 1:1) under ambient conditions, is described. The chiral aryl N-heteroaryl methanols were obtained with up to 98.2% ee by introducing an N-oxide as a removable ortho-substituent. In contrast, no more than 15.1% ee was observed in the absence of an N-oxide moiety. Furthermore, the practical utility of this protocol was also demonstrated by gram-scale asymmetric synthesis of bepotastine besilate in 51% total yield and 99.9% ee.