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.