Stepwise intramolecular cycloaddition of nitrile oxide equivalents derived from the Lewis acid-promoted reaction of 1-nitroalkadienes and allylic stannanes

Abstract

The Lewis acid-promoted reaction of 1-nitroalka-1,5-(or 1,6-)dienes with allylic stannanes has been studied. In the presence of TiCl₄, 1-nitrohexa-1,5-diene reacted smoothly with allyltrimethylstannane to give a diastereoisomeric mixture of 6-allyl-3a,4,5,6-tetrahydro-3H-cyclopent[c] isoxazoles, while the reaction using AlCl₃ as catalyst led to an allylated cyclohexanone oxime derivative in good yield. The similar reaction of 1-nitrohepta-1,6-diene, however, gave a bicyclic dihydroisoxazole irrespective of the Lewis acids employed. In the latter case, nitrite oxide equivalents derived from 1-nitroalka-1,6-dienes underwent a stepwise cycloaddition as shown by the lack of stereospecificity in the reactions of (1E,6Z)-1-nitro-7-phenylhepta-1,6-diene and (1E,6Z)-1-nitro-octa-1,6-diene.