Rhodium(I)-Catalyzed Cyclization of Allenynes with a Carbonyl Group through Unusual Insertion of a C=O Bond into a Rhodacycle Intermediate

Rhodium(I)-catalyzed cyclization of allenynes with a tethered carbonyl group was investigated. An unusual insertion of a CO bond into the C(sp(2))-rhodium bond of a rhodacycle intermediate occurs via a highly strained transition state. Direct reductive elimination from the obtained rhodacyle intermediate proceeds to give a tricyclic product containing an 8-oxabicyclo[3.2.1]octane skeleton, while -hydride elimination from the same intermediate gives products that contain fused five- and seven-membered rings in high yields.