1-(Diphenylphosphoryl)alka-1,2-dienes, bearing aryl substituents at the allene system, under the action of Brønsted (TfOH, H₂SO₄) or Lewis (AlCl₃) acids gave rise to 3-hydroxyalk-2-en-1-yl-diphenylphosphine oxides (diphenylphosphoryl allyl alcohols) in yields of 57–98%. In some cases, the formation of (diphenylphosphoryl)indenes and phosphaheterobicyclic structures was observed.