title: Reversed Stereochemical Control in the Presence of CeCl(3) and TiCl(4) in the Lewis Acid Mediated Reduction of alpha-Alkyl-beta-keto Esters by Metal Hydrides. A General Methodology for the Diastereoselective Synthesis of syn- and anti-alpha-Alkyl-beta-hydroxy Esters.
abstract: The Lewis acid-mediated reduction of alpha-alkyl-beta-keto esters has been shown to proceed by different stereochemical control depending on the nature of the metal atom. Strongly chelating TiCl(4) led to the syn isomer in high diastereomeric excess in noncoordinating solvents (CH(2)Cl(2)) at -78 degrees C with BH(3).py as reducing agent, while nonchelating CeCl(3) gave a high excess of the anti isomer in coordinating solvents (THF) at the same temperature with lithium triethylborohydride (LiEt(3)BH) as reducing agent. The methodology has been successfully utilized for obtaining important syn- and anti-alpha-alkyl-beta-hydroxy esters with high diastereoselectivity.
authors.affiliation: Dipartimento di Chimica, Università della Calabria, I-87030 Arcavacata di Rende, Cosenza, Italy.
authors.forename: Enrico
authors.initials: E
authors.lastname: Marcantoni
authors.forename: Sara
authors.initials: S
authors.lastname: Alessandrini
authors.forename: Marco
authors.initials: M
authors.lastname: Malavolta
authors.forename: Giuseppe
authors.initials: G
authors.lastname: Bartoli
authors.forename: Maria Cristina
authors.initials: MC
authors.lastname: Bellucci
authors.forename: Letizia
authors.initials: L
authors.lastname: Sambri
authors.forename: Renato
authors.initials: R
authors.lastname: Dalpozzo