Organocatalysis with chiral formamides: Asymmetric allylation and reduction of imines

Abstract

Simple aldimine, derived from p-nitrobenzaldehyde and 2-aminophenol, reacts with allyltrichlorosilane in the presence of chiral N-formylproline activator 5 and an L-proline additive to afford the corresponding homoallylic amine in good yield (84%) and with moderate enantioselectivity (43% ee). The role of the second formamide moiety in the activator is crucial to bring about the enhancement in the reaction rate and enantioselectivity, as C-2-chiral bisformamide 1 promotes for the same allylation reaction in higher yield (94%) and enantioselectivity (83% ee). Chiral monoformamide 5 (10 mol-%), with the assistance of HMPA as an additive, also catalyses the asymmetric reduction of ketimine 13 in the presence of trichlorosilane in good yield and enantioselectivity (75%, 81% ee). ((C) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007).