Rhodium(I)-Catalyzed Intramolecular Pauson−Khand-Type [2 + 2 + 1] Cycloaddition of Allenenes

The novel [RhCl(CO)₂]₂-catalyzed [2 + 2 + 1] cycloaddition of allenenes leading to the bicyclo[4.3.0]non-1(9)-en-8-one as well as the bicyclo[5.3.0]dec-1(10)-en-9-one skeletons has been developed. This method also provides a new procedure for the construction of the bicyclo[4.3.0]non-1(9)-en-8-one skeleton having an alkyl appendage at the ring juncture, which was hardly attained in a satisfactory yield by the Pauson−Khand reaction of the corresponding enynes.