Process Research on the Asymmetric Hydrogenation of a Benzophenone for Developing the Manufacturing Process of the Squalene Synthase Inhibitor TAK-475

A practical synthetic method for the synthesis of the chiral benzhydrol 8, which is the key intermediate of the squalene synthase inhibitor TAK-475 (1), has been developed. The method, via asymmetric hydrogenation of the benzophenone 7, employed Noyori's ruthenium precatalyst of the type [RuCl2(diphosphine)(diamine)]. We focused on tuning of the chiral diphosphine, and have discovered a novel ligand, DADMP-BINAP (18c), for the catalyst that has allowed reduction of the operating pressure in the asymmetric hydrogenation. The precatalyst containing 18c performed effectively at low hydrogen pressure (<1 MPa) with sufficient enantioselectivity, and the result enabled us to successfully obtain enantiomerically pure 8 on a multikilogram scale.