New asymmetric approach to natural pyrrolizidines: synthesis of (+)-amphorogynine A, (+)-amphorogynine D, and (+)-retronecine.
Three natural pyrrolizidines, (+)-amphorogynines A and D and (+)-retronecine, have been prepared from a common lactam intermediate. This central compound, in turn, was synthesized in diastereomerically enriched form through a highly selective [2 + 2]-cycloaddition of dichloroketene with a chiral enol ether, followed by Beckmann ring expansion and reduction. Subsequent stereocenters were then cleanly introduced through internal induction.
Roche
Caroline
C
Université Joseph Fourier de Grenoble, Chimie Recherche (LEDSS), 38041 Grenoble Cedex, France.
Kadlecíková
Katarína
K
Veyron
Amaël
A
Delair
Philippe
P
Philouze
Christian
C
Greene
Andrew E
AE
Flot
David
D
Burghammer
Manfred
M
D015394:Molecular Structure; D011763:Pyrrolizidine Alkaloids / Q000138:chemical synthesis* / Q000737:chemistry
D011763:Pyrrolizidine Alkaloids; C476522:amphorogynine A; C511254:amphorogynine D; C014795:retronecine