X=Y-ZH SYSTEMS AS POTENTIAL 1,3-DIPOLES .33. GENERATION OF NITRONES FROM OXIMES - TANDEM MICHAEL ADDITION-1,3-DIPOLAR CYCLOADDITION REACTIONS - CLASS-2 PROCESSES IN WHICH THE DIPOLAROPHILE IS LOCATED WITHIN THE OXIME

C-3, -4, -5, and -6-Alkenyl oximes react with electronegative olefins at the nitrogen atom via a Michael addition or ene-type process to generate the corresponding C-alkenyl nitrones which undergo an intramolecular cycloaddition. The cycloaddition can occur by one of two modes leading to either bridged- or fused-isoxazolidines. The latter is preferred in most cases except that of the C-(3-alkenyl) nitrone which gives exclusively the bridged-ring product and the C-(4-alkenyl)nitrones derived from N-allylpyrrole-2-carboxyaldehyde oxime which gives both bridged- and fused-ring isoxazolidines.