One-pot multiphosphinylation & -phosphonylation of pyridine and related heterocycles towards the synthesis of piperidinylphosphonates and -phosphine oxides

Herein a new protocol for the multiphosphinylation and-phosphonylation of pyridine and related heterocycles is described to give access to piperidinyl phosphine oxides and - phosphonates. The former are accessible through a straightforward, neat, one-pot reaction which yielded the desired phosphinylated heterocycles moderate to excellent yields (42-99%). These compounds contain a high phosphorus to carbon ratio and were evaluated using TGA and calorimetric measurements for potential flame-retardant applications. The respective phosphonates could be obtained using a second protocol, which employed pyridinium salts, triakly phosphites, formic acid and silica to promote the reaction. These piperidinyl phosphonates were isolated moderate to good yields (38-81%) and provide also an interesting starting point for potential enzyme inhibitors.