A Pauson−Khand type conversion of enynes to bicyclic cyclopentenones employing the commercially available precatalyst titanocene dicarbonyl is described. This methodology shows excellent functional group tolerance for a group 4 metallocene-catalyzed process. The scope and limitations of this cyclization with respect to 1,6-, 1,7- and 1,8-enynes with a variety of terminal alkyne substituents, chiral enynes, and enynes containing substituted olefins are described in detail. A mechanism involving carbonylation of an intermediate titanacyclopentene has been proposed.
“Scope of the Intramolecular Titanocene-Catalyzed Pauson−Khand Type Reaction”, J. Am. Chem. Soc., 1999, 121(25), 5881-5898.