overlapping singlets, 6 ), 7.69 (m, 2 ), 8.04 (m, 2 ), 8.63 (s, 2 H); IR (KBr pellet) 1655,1610,1590 cm"1; chemical ionization mass spectrum, m/z 237 (M+ + 1).Conversion of 7b to 8. A stirred solution of 7b (6 mg) in methanol (10 mL) was heated to reflux for 20 h. 1H NMR analysis of the crude concentrated reaction mixture indicated quantitative conversion to 8. 7b was stable in refluxing benzene solution for 12 h.

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The 1,3-dipolar cycloaddition of N-methyl-and IV-phenyl-C-phenylnitrone with several alienes has been investigated. In the case of dimethylallene, a 1:1 mixture of products derived from dipolar cycloaddition across both -bonds was obtained. The formation of a benzazepinone derivative from this reaction was rationalized in terms of a subsequent rearrangement of a transient 5-methyleneisoxazolidine. In contrast to this result, cycloaddition using methoxyallene proceeded with high regioselectivity, giving rise to a 4-(methoxymethylene)-substituted isoxazolidine. The regioselectivity observed is not in agreement with FMO theory, and steric factors do not seem to play a role in the cycloaddition. The reaction of hydroxylamines with carboalkoxyand phenylsulfonyl-substituted alienes was also investigated. The reaction encountered is markedly dependent on the nature of the substituent group present at the 1-position of the aliene. Carboalkoxy-substituted alienes possessing a methyl group react to produce isoxazolin-5-ones. Simple carboalkoxy-substituted alienes, on the other hand, react with nitrones to give a 2:1 cycloadduct derived from a transient nitrone intermediate. The product distribution is probably related to a competition between tautomerization to a nitrone versus lactonization of the transient vinylhydroxylamine produced by addition of hydroxylamine to the aliene.

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