Enantioselective Cyclopropanation of 4-Nitroisoxazole Derivatives

The present study reports an asymmetric organocatalytic cascade reaction of 4-nitroisoxazole derivative with alpha,beta-unsaturated aldehydes catalysed by chiral secondary amine. Using this approach, 1,2,3-trisubstituted cyclopropane products were obtained in isolated yields up to 98% with moderate diastereoselectivities, and enantiopurity up to 99%ee. Moreover, this synthetic protocol can be used for further applications, as shown by a set of additional transformations of the corresponding cyclopropanes and by the formal synthesis of GABA ligands.