Crystallization-induced asymmetric transformation: stereospecific synthesis of L-768,673

Article abstract of DOI:10.1016/S0040-4020(98)01098-9

A highly convergent, asymmetric synthesis of L-768,673, an I_ks Class III antiarrythmic drug candidate, is described. Synthesis of the racemic 1-trifluoroethyl-3-amino-5-phenyl benzodiazepinone <(+/-)-amine> was achieved by Ru-catalyzed hydrogenation of the corresponding oxime that was derived from commercially available 1-trifluoroethyl-5-phenyl benzodiazepine in 76 percent overall yield. An efficient one-pot resolution-racemization of (+/-)-amine provided the desired (+)-amine as its mandelate salt in 92 percent yield and 99.4 percent ee. Regioselective ortho-lithiation of 1,3-bis(trifluoromethyl)benzene with n-BuLi in the presence of a catalytic amount of 2,2',6,6'-tetramethylpiperidine afforded its aryl lithium. Subsequent transmetalation and alkylation with allyl bromide produced the corresponding olefin. Ru-catalyzed oxidative cleavage of the terminated double bond of the olefin provided the desired 2,4-bis(trifluoromethyl)phenylacetic acid in 35 percent overall yield. A modified Schotten-Baumman procedure was developed for coupling of (+)-amine and the acid to produce L-768,673 in 92 percent yield without racemization. - Keywords: Asymmetric synthesis; Benzodiazepines; Oximes; Resolution-racemization