Reduction of beta-enamino ketones 1 with NaBH(OAc)3 in glacial acetic acid gave beta-amino ketones 3 in 65% to 67% yield. These data and others observed in the reduction of beta-enamino ketones 1 to preferentially syn gamma-amino alcohols 2 with NaBH4/HOAc suggest that in this last reaction we have firstly the reduction of the beta-enamino ketones 1 to produce the beta-amino ketones 3, and then this compound is reduced to the gamma-amino alcohols 2. We can say from this results that the diastereosselectivity of the reduction of beta-enamino ketones 1 to mainly syn gamma-amino álcohols 2, can be analysed as a competition between a chair-like transition state and a boat-like transition state, obtained from the beta-amino ketones 3.
amino alcohols; enamino ketones; amino ketones; Mannich base
