Rhodium-catalyzed cascade reaction of 1,6-enynes involving addition, cyclization, and β-oxygen elimination

The reaction of arylboronic acids with 1,6-enynes that contain an allylic ether moiety is catalyzed by a rhodium(I) complex to produce cyclopentanes with a tetrasubstituted exo olefin and a pendant vinyl group. The reaction is initiated by the regioselective addition of an arylrhodium(I) species to the carbon-carbon triple bond of the 1,6-enyne. The resulting alkenylrhodium(I) compound subsequently undergoes intramolecular carborhodation of the allylic double bond in a 5-exo-trig mode. β Elimination of the methoxy group affords the cyclization product and the catalytically active methoxorhodium(I) species. The use of alkyl Grignard reagents instead of arylboronic acids as organometallic nucleophiles was also examined.