Reduction of Triphenylphosphine Oxide to Triphenylphosphine by Phosphonic Acid.

A novel method for the iodine-mediated reduction of phosphine oxides (sulfides) to phosphines using phosphonic acid under solvent-free conditions is described. By using a combination of H 3 PO 3 and I 2 , both tertiary monophosphine oxides and bis-phosphine oxides were reduced under this system, readily producing monodentate and bidentate phosphines, respectively, in good yields. Notably, chiral ( R )-(+)-2,2'-bis(diphenylphosphino)-1,1'-binaphthyl dioxide could be also tolerated without racemization. This new approach is inexpensive and features simple conditions and a wide substrate scope.