A simple primary-tertiary diamine-Bronsted acid catalyst for asymmetric direct Aldol reactions of linear aliphatic ketones

Compared with the well-explored enamine catalysis with secondary amines, the development of efficient enamine-based primary amine catalysts has remained as an elusive goal until recently. We present herein that a simple chiral primary-tertiary diamine 1d in combination with TfOH acts as an efficient enamine-based primary amine catalyst. The 1d-TfOH catalytic system could effectively catalyze the asymmetric direct aldol reaction with broad substrate scope as well as high regio- and diastereoselectivity and enantioselectivity under ambient temperature. Significantly, the reactions accommodate the synthetically important but challenging substrates, such as linear aliphatic ketones, with high regioselectivity and unprecedented syn diastereoselectivity. These results are in sharp contrast with the secondary amine mediated similar reactions wherein anti diastereoselectivity was normally observed.