Nm. Kablaoui et Sl. Buchwald, DEVELOPMENT OF A METHOD FOR THE REDUCTIVE CYCLIZATION OF ENONES BY A TITANIUM CATALYST, Journal of the American Chemical Society, 118(13), 1996, pp. 3182-3191
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.