Novel Alternative for the NN Bond Formation through a PIFA-Mediated Oxidative Cyclization and Its Application to the Synthesis of Indazol-3-ones

The synthesis of a series of N,N-disubstituted indazolone derivatives starting from methyl anthranilates is presented. This general approach features a novel and easy way for access to the target N-heterocycles by formation of a new NN single bond. The key cyclization step embraces the formation of an N-acylnitrenium intermediate, mediated by the hypervalent iodine reagent PIFA, and its succeeding intramolecular trapping by the amine moiety under rather mild experimental conditions.