Intramolecular Pauson-Khand reactions of alpha,beta-unsaturated esters and related electron-deficient olefins.

The intramolecular Pauson-Khand (PK) reaction of a variety of electron-poor enynes having an ester, cyano, or phosphonate group at the olefin terminus is described. Depending on the reaction conditions and substitution at the enyne, their dicobalthexacarbonyl complexes led preferentially to the exocyclic 1,3-diene or to the PK cyclopentenone product. In general, the 1,3-diene was obtained as the major product under N-oxide-promoted conditions, while the PK product was selectively formed in refluxing acetonitrile.