Nitro alkene Enantioselective conjugate addition

In 2009, Bernadi and Adamo designed 4-nitro-5-sttyrylisoxazole (66) as a novel Michael acceptor. The asymmetric conjugate addition of nitroalkanes to 66 in the presence of cinchonidine-derived PTC catalyst 8o afforded the addition adduct 67 with high enantioselectivity (97% enantiomeric excess). The 4-nitroisoxazole eore serves as an activator of the conjugated alkene and is readily derivatised to pharmaceutically valuable compounds, such as y-nitroesters and y-amino acids (Scheme 16.20). " ... 

Song and coworkers compared the squaramide 31 with the sulfonamide 28 and the related C9 thiourea derivative as catalyst for the conjugate addition of 1,3-dicarbonyls to [i-nitroalkenes in brine [89] and the conjugate addition of malonic acid half thioester to various nitro alkenes [90]. In the latter reaction (Scheme 6.41), 31 afforded the best results with respect to enantioselectivity that is, the ee was 93% for 31 but only 63% for thiourea and 23% for the sulfonamide analog. 

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