title: Enamino Ester Reduction: A Short Enantioselective Route to Pyrrolizidine and Indolizidine Alkaloids. Synthesis of (+)-Laburnine, (+)-Tashiromine, and (-)-Isoretronecanol.
abstract: Various chiral pyrrolidine tetrasubstituted beta-enamino esters were reduced catalytically or chemically with good to moderate diastereoselectivity owing to a chiral induction originated from (S)-alpha-methylbenzylamine. With endocyclic double bond compounds, the best result was obtained using PtO(2) as hydrogenation catalyst and led to a major syn addition product (e.d. 90%). In the case of exocyclic double bond compounds, hydrogenation over Pd/C gave rise to the higher diastereoselectivity and mainly afforded the unexpected anti addition product (e.d. 84%). The scope of these reductions has been extended to the synthesis of three pyrrolizidine or indolizidine alkaloids: (+)-tashiromine, (+)-laburnine, and (-)-isoretronecanol. Syntheses of these natural products, starting from chiral beta-enamino diesters, were achieved in a short and convenient manner, leading to enantiopure compounds in good overall yields.
authors.affiliation: Laboratoire de Chimie des Hétérocycles, UMR 7611, Université P. et M. Curie (Boîte 43), 4 Place Jussieu, 75252 Paris Cedex 05, France.
authors.forename: Olivier
authors.initials: O
authors.lastname: David
authors.forename: Jérôme
authors.initials: J
authors.lastname: Blot
authors.forename: Christian
authors.initials: C
authors.lastname: Bellec
authors.forename: Marie-Claude
authors.initials: MC
authors.lastname: Fargeau-Bellassoued
authors.forename: Gjergj
authors.initials: G
authors.lastname: Haviari
authors.forename: Jean-Pierre
authors.initials: JP
authors.lastname: Célérier
authors.forename: Gérard
authors.initials: G
authors.lastname: Lhommet
authors.forename: Jean-Claude
authors.initials: JC
authors.lastname: Gramain
authors.forename: Daniel
authors.initials: D
authors.lastname: Gardette