A Versatile Protocol for the Quantitative and Smooth Conversion of Phosphane Oxides into Synthetically Useful Pyrazolylphosphonium Salts

A convenient protocol for the smooth conversion of the resistant PO bond in phosphane oxides into a reactive PN bond of synthetically useful pyrazolylphosphonium salts is described. A highly charged, oxophilic, phosphorus‐centered trication is employed and the reactions are conducted at room temperature with quantitative yields. The resulting pyrazolylphosphonium cations are valuable synthetic intermediates and are used for the synthesis of a variety of organophosphorus compounds. This represents a new approach towards the transformation of the rather inert phosphoryl group under very mild reaction and workup conditions and aims towards alternatives to existing reduction methods for phosphane oxide functionalization. Going uphill: A protocol for the smooth conversion of the resistant PO bond in phosphane oxides into a reactive PN bond of synthetically useful pyrazolylphosphonium salts by a highly‐charged, oxophilic phosphorus‐centered trication is described. The reactions are conducted at room temperature with quantitative yields. We aim towards alternatives to existing reduction methods for phosphane oxide functionalization.