Enamino Ester Reduction: A Short Enantioselective Route to Pyrrolizidine and Indolizidine Alkaloids. Synthesis of (+)-Laburnine, (+)-Tashiromine, and (-)-Isoretronecanol.
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.
David
Olivier
O
Laboratoire de Chimie des Hétérocycles, UMR 7611, Université P. et M. Curie (Boîte 43), 4 Place Jussieu, 75252 Paris Cedex 05, France.
Blot
Jérôme
J
Bellec
Christian
C
Fargeau-Bellassoued
Marie-Claude
MC
Haviari
Gjergj
G
Célérier
Jean-Pierre
JP
Lhommet
Gérard
G
Gramain
Jean-Claude
JC
Gardette
Daniel
D