The reaction of 1-alkyl-3-phenylpropynones with aromatic aldehydes: an update

1-Alkyl-3-phenylprop-2-yn-1-ones smoothly react with aromatic aldehydes in the presence of triphenylphosphine (acetonitrile, room temperature, 24 h) to regio- and stereo- selectively afford (Z)-2-benzylideneoxacyclopentan-3-ones in yields up to 93%. The proposed mechanism for the transformation involves 1,3-H proton shift from the alkyl group at the intermediate β-phosphoniovinylide species.