Rh(I)-Catalyzed Intramolecular Allenic Pauson−Khand Reaction:  Construction of a Bicyclo[5.3.0]dec-1,7-dien-9-one Skeleton

1-Phenylsulfonylallenes possessing a hexynyl appendage in refluxing toluene in the presence of catalytic amount of rhodium(I) catalyst under a carbon monoxide atmosphere underwent regioselective formal [2 + 2 + 1]-cycloaddition to produce the corresponding bicyclo[5.3.0]dec-1,7-dien-9-one derivatives in acceptable yields.