Asymmetric reduction of prochiral cyclic imines to alkaloid derivatives by novel asymmetric reducing reagent in THF or under solid-state conditions

Asymmetric reductions of prochiral cyclic imines were studied using chiral nonracemic sodium acyloxy borohydride 2. The chiral nonracemic reducing agent 2 has been easily prepared by the reaction of NaBH(4) with N,N-phthaloyl amino acid 1 in THF. The reagent reduces the prochiral cyclic imines 3 and 5 to the alkaloid derivatives 4 and 6 in good enantioselectivity (65-75% ee). The reduction of prochiral cyclic imines with the reagent in the presence of ZnCl(2) or under solid-state conditions showed higher enantioselectivity (83-100% ee).