A convenient and efficient synthesis of spiro-fused pyrazolin-5-one N-oxides starting from readily available 1-carbamoyl-1-oximylcycloalkanes is developed. This general protocol features a novel and facile way for access to the five-membered azaheterocycles by formation of a new N-N single bond. The key cyclization step utilizes the formation of an N-oxonitrenium intermediate, mediated by the hypervalent iodine reagent PIFA, and its subsequent intramolecular trapping by the amide moiety under rather mild experimental conditions.

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The regiospecific β-lactam ring-opening/recyclization reaction of N-aryl-3-spirocyclic-β-lactams, made by the one-pot cyclization reaction of acetoacetanilides, has been achieved for the first time using a Lewis-Brønsted acids combined superacid catalyst system, thus providing an efficient entry to 3-spirocyclicquinolin-4(1H)-ones. A mechanism involving superacid-catalysis was proposed.