Divergent synthesis of nitrocyclopropanes and isoxazoline N-oxides from nitro compounds and vinyl sulfonium salts

Abstract

New annulation reactions involving aliphatic nitro compounds and vinyl sulfonium salts are described. Selective methods are proposed to control the direction of the reaction by changing the solvent and the base. The use of DBU in EtOAc resulted in predominant cyclopropane ring closure, while Et₃N in CF₃CH₂OH selectively afforded isoxazoline N-oxides. A broad substrate scope was demonstrated, and a series of nitrocyclopropanes and isoxazoline N-oxides were synthesized in high yields. The developed methodology is effective, tolerant toward many functional groups, and easy to implement in practice. The observed selectivity was probed by DFT calculations, showing the importance of both the solvent and the base. The synthetic value of the resulting products was demonstrated by the selective reduction of the nitro group, selective C–C bond cleavage, as well as some other transformations.