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Stereoselective Synthesis of 1-Nitrobicyclo[3.1.0]hexanes and Fused Isoxazoline-N-oxides from Primary Nitro Compounds

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posted on 02.03.2012, 00:00 by Akio Kamimura, Ryota Takeuchi, Kosuke Ikeda, Takaaki Moriyama, Michinori Sumimoto
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 Ag2O and iodine under basic conditions. We observed that when a primary alkyl group was present at the β-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.