Asymmetric Michael Addition of α-Hydroxyketones to Nitroolefins Catalyzed by Chiral Diamine
摘要:
[GRAPHIC]The regio-, stereo-, and enantioselective direct Michael addition of alpha-hydroxyketones to beta-aryinitroolef ins catalyzed by N-/Pr-2,2'-bipyrrolidine is described. The formation of an internal hydrogen bond between the OH group of alpha-hydoxyacetone and the tertiary nitrogen of the catalyst leads to the formation of a rigid cis enamine intermediate that explains the inversion of the expected diastereoselectivity and the very high ee's.
The direct Michaeladdition of aldehydes and ketones to nitroolefins, catalyzed by N-i-Pr-2,2′-bipyrrolidine, is described. The desired 1,4-adducts are obtained in excellent yields with enantioselectivities up to 95% ee and dr up to 95 : 5 of the syn aldehydeaddition product. An unexpected inversion of diastereoselectivity was observed for the addition of α-hydroxy ketones to β-arylnitroolefins with