One-pot reductive coupling of N-acylcarbamates with activated alkenes: application to the asymmetric synthesis of pyrrolo[1,2-a]azepin-5-one ring system and (−)-xenovenine
cyclic N-acylcarbamates can be used as stable substrates, and a range of activated alkenes serve as effective radical receptors. The reductive coupling of l-N-acylcarbamates 12/13 gave 2,5-disubstitutedpyrrolidine derivatives in high trans-diastereoselectivities. The reductive coupling with penta-2,4-dienoate proceeded exclusively in a 1,6-addition fashion, producing a single non-conjugated E-isomer
A two-directional approach to pyrrolizidines: total syntheses and biological evaluation of alkaloid cis-223B and (±)-xenovenine
作者:Alexandre Barthelme、David Richards、Ian R. Mellor、Robert A. Stockman
DOI:10.1039/c3cc46800c
日期:——
Totalsyntheses of alkaloid cis-223B and xenovenine are reported in 3 and 4 steps respectively using a two-directional synthesis/triple reductive amination strategy, and their neurotoxic properties assessed.
Highly Stereoselectivetrans Addition of π-Type Nucleophiles to a BicyclicN-Acyliminium Ion – Application to the Synthesis of Indolizidine and Pyrrolizidine Alkaloids
usefulness of this stereoselective access to trans-2,5-disubstituted pyrrolidines was illustrated by formal syntheses of 3,5-disubstituted indolizidine toxins, starting from 5-allyltetrahydropyrrolo[1,2-c]oxazol-3-one 2a. Moreover, an enantiodivergent synthesis of the pyrrolizidine alkaloids (+) and (–)-xenovenine was achieved starting from the same chiral building block 2a.
Synthesis of dihydropyrroles by the intramolecular addition of alkylideneaminyl radicals generated from O-2,4-dinitrophenyloximes of γ,δ-unsaturated ketones
Alkylideneaminyl radicals are generated from O-2,4-dinitrophenyloximes of γ,δ-unsaturated ketones by treatment with NaH and 3,4-methylenedioxyphenol. The resulting radical species successively add to the olefinic moiety intramolecularly to afford dihydropyrroles in the presence of a radical trapping agent. This method is applied for the stereoselective synthesis of xenovenine, a bicyclic 3,5-dialkylpyrrolizidine
Diastereo- and enantioselective syntheses of (−)-coniine, (−)-solenopsin A, (−)-solenopsis fugaz venom and (−)-xenovenine via deoxygenative decarboxylation of 2-carbonylsultam-substituted n-hydroxy-piperidines and -pyrrolidines
作者:Wolfgang Oppolzer、Christian G. Bochet、Eric Merifield
DOI:10.1016/0040-4039(94)88213-4
日期:1994.9
Heating cyclic 2-carbonylsultam-substituted N-hydroxylamines 4 with NaH yields sultam auxiliary 8 and imines 10, which are trapped in situ either by i-Bu2AlH or organocerium reagents to give enantiomerically pure 2-mono- or trans-2,6(2,5)-disubstituted piperidines (pyrrolidines) 11 or 12.