Michael addition Brpnsted base catalysis

Other nucleophiles such as nitromethane can also be used for this reaction. Thus, by the catalysis of (fl)-LPB (LaK3tris((/ )-binaphthoxide) (20 mol %), in which La works as a Lewis acid and K-naphthoxide works as a Brpnsted base, nitromethane reacted with chalcone to give the Michael adduct in 85% yield and 93% ee (Scheme 8D.8) [22], Addition of BuOH (120 mol %) gave a beneficial effect on the reactivity as well as the enantioselectivity of this reaction. 

During the last years, organocatalytic asymmetric aza-Michael additions have been thoroughly investigated [62, 63] employing different types of organocatalysis (amine, Brpnsted base, Brpnsted acid, PTC, and enzymatic catalysis). 

Chen et al. [26] reported the use of a bifunctional thiourea catalyst 61 during the organocatalyzed thia-Michael addition of thiophenol to unsaturated imide 58c (Scheme 3.29). Michael adduct 60c was obtained in 60% ee and 97% yield by conducting the reaction in dichloromethane at -78°C. The authors speculated that while the tertiary amine of the bifunctional catalyst 61 would act as a proton shuttle according to a Brpnsted acid/base catalysis, the presence of the thiourea moiety might possibly cooperate in the stabilization of the more stable Z-enolate intermediate via hydrogen bond formation as illustrated in Scheme 3.31. 

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