Synthesis of\nHydrazonyl Sultones via Phosphine-Mediated\nCyclodehydration of Vicinal Sulfo-acyl Hydrazides

We report a phosphine-mediated cyclodehydration\nprocedure\nfor the\nfacile synthesis of <i>N</i>-aryl/alkyl-substituted hydrazonyl\nsultones, a class of bioorthogonal reagents, from the readily prepared\nvicinal sulfo-acyl hydrazides in moderate to good yields. The aqueous\nstability and bioorthogonal reactivity of these hydrazonyl sultones\ntoward bicyclo[6.1.0]non-4-yn-9-ylmethanol were investigated, revealing\nkey structural requirements for hydrazonyl sultones to possess balanced\nstability and reactivity.