Stereospecific formal [3+2] dipolar cycloaddition of cyclopropanes with nitrosoarenes: an approach to isoxazolidines.

The MgBr2-catalyzed formal [3+2] cycloaddition of donor-acceptor activated cyclopropanes with nitrosoarenes offers a novel approach to various structurally diverse isoxazolidines. The reactions, which are experimentally easy to conduct, occur with complete stereospecificity and perfect control of regioselectivity. Product isoxazolidines can be readily transformed into α-amino lactones by reductive or decarboxylative N-O cleavage and subsequent lactonisation, and the N-aryl bond cleavage is also possible under oxidative conditions.