Nitro-olefins as Acceptors

However, more active and selective eatalysts are adamantyl-L-prolinamide 36, and camphor-lO-sulfonamide-based prolinamides 37, which contain additional stereocentres. Prolinamides derived from bile acids such as epiandrosterone 38, or cholic acid 39 ° exert good enantiocontrol, probably because the cholestanic structure that forms a functionalised chiral cavity with the appended prolinamide groups that were able to exert a good stereocontrol on the orientation of the substrate. 

Prolinamide derivative 40 and (5 )-l,10-bi-2-naphthol was found to be the most effeetive eombination for the addition of aldehydes to nitro-olefins affording the addition products with excellent yields and stereoselection (ee and de up to 99%). 

Various i-prolinamides, derived from chiral p-amino alcohols, are active hifunctional catalysts for nitro-Michael additions of ketones to p-nitrostyr-enes. In particular, catalyst 25e exhibits the highest catalytic performance working in polar aprotic solvents. 

Sugar-hased prolinamide 16m has also been employed as catalyst for the asymmetric Michael addition of cyclohexanones to p-nitroslyrenes. During optimisation of the reaction conditions, the authors found that the polarity of the solvent does not modify the yield or stereoselectivity, but the best ee was obtained under neat conditions at -20 °C. Ammonium ionic liquids 41a,b are also efficient organocatalysts for the asymmetric Michael addition of aldehydes to nitro-olefins giving the adducts with excellent yields and enantioselectivities and modest to high diastereoselectivities. 

Four peptidomimics 42 were synthesised by Gennari and tested as organocatalysts in the addition of several aldehydes to p-nitrostyrene and (J7)-2-(furan-2-yl) nitroethene with good to excellent diastereo- and enantioselectivities. 

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Importantly, prolinamide catalysts (Figure 6.3) work well in Michael addition reactions using nitro-olefins as acceptors. iV-Tritylprolinamide 33 and aminonaphthyridine-derived ProNap 34 served as organocatalysts in asymmetric Michael additions of aldehydes and cyclohexanone to nitro-alkenes. Proline-functionalised C3-symmetric 1,3,5-triallq lbenzene 35 was screened in the reaction of cyclohexanone to nitrostyrene to afford the Michael adducts in good yields and diastereoselectivity but low enantioselectivity. 

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