Oxidation of a P−C Bond under Mild Conditions

The reactivity of phosphenium dication [(Ph 3 P) 2 C‐P‐N i Pr 2 ] 2+ , 1 2+ , towards pyridine N‐oxide (O‐py) has been investigated. The resulting oxophosphonium dication [(Ph 3 P) 2 C(N i Pr 2 )P(O)(O‐py)] 2+ , 2 2+ , 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.