Prochiral compounds Michael addition

The chiral, nonracemic oxazepine derivative (46 Scheme 18) was studied as donor in the Michael addition to prochiral a,p-unsaturated carbonyl compounds.134-133 The products were obtained with 44-55% ee after removal of the chiral auxiliary group. With 1-nitrocyclohexene as acceptor, somewhat better se-lectivities (62% ee) were observed.136... 

Michael addition of 1,3-dicarbonyl compounds to conjugated prochiral nitroalkenes catalysed by (acac)2Ni and (acac)2Co has been reported to give up to 30% ee when carried out in the presence of cinchonidine.100... 

The cation fragment nature exerts negligible impact on selectivity of the Michael reactions that involve enamine intermediates and commonly the stereochemical outcome remains high. Indeed, pyrrolidine derivatives (Figure 22.6) containing pyridinium 87a,b [98], isoquinolinium 88a,b [99], 1,2,3-triazolium 89a,b [100], benzimidazolium 90 [101], and linear 91 [102] or cyclic 92 [103] quaternary ammonium cations in combination with various anions proved efficient catalysts of asymmetric additions of carbonyl compounds to a-nitro alkenes. Desymmetriza-tion of prochiral 4-substituted cyclohexanones can be achieved by analogy [101]. The reaction efficacy was similar under neat conditions in the presence of acidic additives (catalysts 87, 89, 90, 91) or in the IL medium (commonly in [bmim]BF4) (catalysts 88a,b, 92). 

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