Synthesis of Hydrazonyl Sultones via Phosphine-Mediated Cyclodehydration of Vicinal Sulfo-acyl Hydrazides

We report a phosphine-mediated cyclodehydration procedure for the facile synthesis of <i>N</i>-aryl/alkyl-substituted hydrazonyl sultones, a class of bioorthogonal reagents, from the readily prepared vicinal sulfo-acyl hydrazides in moderate to good yields. The aqueous stability and bioorthogonal reactivity of these hydrazonyl sultones toward bicyclo[6.1.0]non-4-yn-9-ylmethanol were investigated, revealing key structural requirements for hydrazonyl sultones to possess balanced stability and reactivity.