title: Asymmetric aldol reactions using (S,S)-(+)-pseudoephedrine-based amides: stereoselective synthesis of alpha-methyl-beta-hydroxy acids, esters, ketones, and 1,3-Syn and 1,3-anti diols
abstract: A very efficient method for performing stereoselective aldol reactions is reported. The reaction of (S, S)-(+)-pseudoephedrine-derived propionamide enolates with several aldehydes yielded exclusively one of the four possible diastereomers in good yields, although transmetalation of the firstly generated lithium enolate with a zirconium(II) salt, prior to the addition of the aldehyde, is necessary in order to achieve high syn selectivity. The so-formed syn-alpha-methyl-beta-hydroxy amides were transformed into other valuable chiral nonracemic synthons such as alpha-methyl-beta-hydroxyacids, esters, and ketones. Finally, a stereocontrolled reduction procedure starting from the so-obtained alpha-methyl-beta-hydroxy ketones has been developed allowing the synthesis of either 1,3-syn- or 1,3-anti-alpha-methyl-1,3-diols in almost enantiopure form by choosing the appropriate reaction conditions.
authors.affiliation: Departamento de Quimica Organica, Facultad de Ciencias, Universidad del Pais Vasco, P.O. Box 644, 48080 Bilbao, Spain.
authors.initials: JL
authors.lastname: Vicario
authors.initials: D
authors.lastname: Badia
authors.initials: E
authors.lastname: Dominguez
authors.initials: M
authors.lastname: Rodriguez
authors.initials: L
authors.lastname: Carrillo