Sacrificial azomethine ylide cycloaddition controlled chemoselective nitrile oxide cycloaddition to 1-methyl-3,5-bis[(E)-arylmethylidene]tetrahydro-4(1H)-pyridinones: formation of mono-spiro-isoxazolines

The 1,3-dipolar cycloaddition of an azomethine ylide to 1-methyl-3,5-bis[(E)-arylmethylidene]tetrahydro-4(1H)-pyridinones afforded novel spiro-pyrrolidines in good yields. Further cycloaddition of these spiro-pyrrolidines with nitrile oxide afforded mono-spiro-isoxazolines in moderate yields (45–56%), presumably via a di-spiro intermediate, which undergoes a spontaneous cycloreversion of the spiro-pyrrolidine unit. In contrast, the direct cycloaddition of nitrile oxide to 1-methyl-3,5-bis[(E)-arylmethylidene]tetrahydro-4(1H)-pyridinones gave the mono-spiro-isoxazoline as the minor product, while the bis-spiro-isoxazolines are formed predominantly.