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 spiropyrrolidine 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. (c) 2007 Elsevier Ltd. All rights reserved.