Asymmetric desymmetrization of the diallyl acetals of alkynal (1) by an enantioselective Pauson–Khand-type reactioncatalyst was studied. The corresponding 5-oxabicyclo[3.3.0]octenones (2) were obtained as a mixture of diastereomers (2a and 2b), which were hydrolyzed to afford a single enantiomer (3), in high yields (up to 88%) as well as excellent enantioselectivities (up to 97%).