Synthesis of 1,2,3-Triphospholenes, 1,2-Diphosphetes, and Unsymmetric Phospholes by Rhodium-catalyzed Cleavage of P−P Bonds and Addition to Alkynes

The rhodium-catalyzed addition reaction of cyclo-(PPh)₅ to alkynes in refluxing THF efficiently provide 1,2,3-triphospholenes, in which the –PPh–PPh–PPh– group is transferred from cyclo-(PPh)₅ by the cleavage of P−P bonds. In refluxing chlorobenzene, the reactions are accompanied by the formation of 1,2-diphosphetes. When the triphospholenes containing P−P bonds are reacted with reactive alkynes under rhodium-catalyzed conditions, unsymmetric phospholes are obtained. The rhodium-catalyzed reactions can be used to synthesize various phosphorus-containing heterocycles with different numbers of phosphorus atoms.