DEVELOPMENT OF A METHOD FOR THE REDUCTIVE CYCLIZATION OF ENONES BY A TITANIUM CATALYST

An effective protocol in which bis(trimethylphosphine)titanocene is us ed to catalyze the reductive cyclization of enones to cyclopentanols v ia a metallacyclic intermediate has been developed. The key step in th e process is the cleavage of the titanium-oxygen bond in the metallacy cle by a silane to regenerate the catalyst. Mechanistic aspects of the reaction are discussed and the diastereoselectivity of the transforma tion is studied using both achiral and chiral substrates. The scope an d limitations of the procedure are described. An in situ protocol for the generation of the air- and moisture-sensitive catalyst has also be en developed. This work demonstrates, for the first time, the viabilit y of using an early transition metal complex to catalyze the reductive cyclization of an alkene with a heteroatom-containing functional grou p.