Oxidation of a P-C Bond under Mild Conditions

The reactivity of phosphenium dication [(Ph₃P)₂C-P-NiPr₂]²⁺, 1²⁺, towards pyridine N-oxide (O-py) has been investigated. The resulting oxophosphonium dication [(Ph₃P)₂C(NiPr₂)P(O)(O-py)]²⁺, 2²⁺, was surprisingly stabilized by a less nucleophilic O-py ligand instead of pyridine (py). This compound was then identified as an analogue of the elusive Criegee intermediate as it underwent oxygen insertion into the P-C bond through a mechanism usually observed for Baeyer-Villiger oxidations. This oxygen insertion appears to be the first example of a Baeyer-Villiger oxidation involving O-py.