Reversal of enantioselectivity using tethered bisguanidine catalysts in the aza-Henry reaction

A series of chiral guanidines were synthesized and shown to efficiently catalyze the aza-Henry reaction. Modifications of the catalyst Structure revealed important selectivity trends as well as an intriguing reversal in stereoselectivity with bisguanidine variants. These compounds were applied to the aza-Henry reaction between N-Boc imines and nitroalkanes generating the beta-nitroamines in up to 77% ee and up to 20:1 diastereoselectivity. (C) 2009 Elsevier Ltd. All rights reserved.