Highly Chemoselective Reduction of Phosphine Oxides through Electrophilic Activation of the P=O Bond with Anhydride

A highly chemoselective reduction of phosphine oxides was demonstrated under transition-metal-free and alkaline reaction conditions. During the reaction, P=O bond was firstly electrophilically activated by an anhydride and subsequently reduced by the versatile and cheap NaH, which was strengthened by 15-crown-5. By this strategy, a variety of phosphine oxides including those bearing functional groups such as methyl, methoxyl, phenyl, fluorine, chlorine, bromine, iodine, trifluoromethyl, nitrile, ester, alkenyl, alkynyl and heterocycles were transformed readily into the corresponding phosphines in good to high yields. This work represents an efficient method for reducing phosphine oxides forming phosphines.