A study of the reactivity of a series of 4-diazopyrazolin-5-ones toward dipolar cycloaddition with electron-deficient olefinic and acetylenic dipolarophiles has been carried out. Reactions with dimethyl acetylenedicarboxylate afford pyrazolo [1, 5-d][1, 2, 4] triazin-7-ones which result from dipolar cycloaddition followed by a van Alphen-Huttel rearrangement of the initially produced spiro 3H-pyrazole adducts. Reaction with unsymmetrical acetylenic ...
