An unusual phosphide addition reaction of 1,3-dimethyl-1,2,3-benzotriazolium iodide

Abstract

The reactivity of the stable N-heterocyclic nitrenium salt 1,3-dimethyl-1,2,3-benzotriazolium iodide (1) toward various nucleophilic reagents has been investigated. Strongly nucleophilic reagents such as potassium hydride (KH), potassium cyclopentadienide (KCp), potassium tert-butoxide (KOtBu), sodium methoxide (NaOMe), and sodium ethanethiolate (NaSEt) all reacted with 1 under demethylation and back-formation of 1-methyl-1,2,3-benzotriazole (2) in high isolated yield (ca. 80–90%). In marked contrast, an unusual phosphide addition reaction took place when 1 was treated with 1 equiv. of potassium diphenylphosphide (as the 1,4-dioxane adduct KPPh2(dioxane)2). In the course of this reaction the P atom replaces the central nitrogen of the triazole ring while being formally oxidized to an iminophosphorane derivative (3). Both compounds 2 and 3 have been structurally characterized through single-crystal X-ray diffraction.