Stereoselective synthesis of 1-nitrobicyclo[3.1.0]hexanes and fused isoxazoline-N-oxides from primary nitro compounds.

ABSTRACT

The one-step preparation of 1-nitrobicyclo[3.1.0]hexane and bicycloisoxazoline-N-oxide was readily achieved from conjugate adducts of nitro alkenes and allylmalonates by treatment with Ag(2)O and iodine under basic conditions. We observed that when a primary alkyl group was present at the ß-position of the nitro group, bicyclo[3.1.0]hexane was preferentially formed, whereas if a secondary alkyl group occupied that position, isoxazoline-N-oxide was predominantly produced. High cis-selectivity was observed for the formation of cyclopentane units for both reactions. An iodomethyl adduct, considered an intermediate of the cyclization, was isolated, and its conversion to isoxazoline-N-oxide was successfully achieved. The isoxazoline-N-oxide underwent 1,3-dipolar cycloaddition with alkenes to yield tricycloheterocyclic compounds, which were readily converted to spirolactam in good yield by reductive cleavage of N-O bonds using Raney-Ni. On the other hand, 1,3-dipolar cycloaddition of the isoxazoline-N-oxide to terminal alkynes yielded tricyclic aziridines stereoselectively.