Selective reduction of allenyl(diphenyl)phosphine oxides to allyl(diphenyl)phosphine oxides

The reduction of allenyl(diphenyl)phosphine oxides with HSiCl3 or LiAlH4 selectively afforded the corresponding allyl(diphenyl)phosphine oxides. 3-Methylbut-2-en-1-yl(diphenyl)phosphine oxide reacted with AlCl3 to give a mixture of 4,4-dimethyl-1-phenyl-1,2,3,4-tetrahydro-λ5-phosphinoline 1-oxide and 4,4-dimethyl-1-phenyl-1,4-dihydro-λ5-phosphinoline 1-oxide.