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All total 9 Articles be found
All total 9 Articles be foundAn efficient route to the pyrrolizidine ring system via an N-acyl anion cyclisation process
Murray, Anthony,Proctor, George R.,Murray, P. John
, p. 3757 - 3766 (1996)
An enantioselective route to the pyrrolizidine ring system has been developed which uses an N-acyl anion cyclisation reaction as the key step. This methodology has provided the natural pyrrolizidines (-)-(1R, 8S)-1-hydroxy-pyrrolizidine 7, (-)-pyrrolizidin-1-ene-3-one 9 and (±)-trachelanthamidine 14. Extension of the process to an N-propionyl substrate provides ready access to a series of 2-methyl pyrrolizidines.
Enantioselective catalytic desymmetrization of maleimides by temporary removal of an internal mirror plane and stereoablative over-reduction: Synthesis of (R)-pyrrolam A
Marsh, Barrie J.,Adams, Harry,Barker, Mike D.,Kutama, Ibrahim U.,Jones, Simon
supporting information, p. 3780 - 3783 (2014/08/05)
A highly enantioselective (>95% ee) strategy to affect the desymmetrization of a maleimide has been performed by temporary attachment to an anthracene template followed by asymmetric reduction with an oxazaborolidine catalyst. A stereoablative over-reduction process was partially responsible for the high levels of enantioselectivity. Exemplification of the strategy by stereoselective functionalization and retro-Diels-Alder reaction provided the natural product pyrrolam A.
Enantioselective synthesis of condensed and transannular ring skeletons containing pyrrolidine moiety
Mo, Fanyang,Li, Fei,Qiu, Di,Wang, Jianbo
experimental part, p. 1274 - 1279 (2010/03/30)
A new approach toward condensed and transannular ring structures containing pyrrolidine unit has been developed, based on diastereoselective nucleophilic addition of lithium enolate of α-diazoacetoacetate to chiral N-sulfinyl imine and ring-closing metathesis.
Synthesis of (-)-(R)-pyrrolam A and studies on its stability: A caveat on computational methods
Watson, Rhett T.,Gore, Vinayak K.,Chandupatla, Kishan R.,Dieter, R. Karl,Snyder, James P.
, p. 6105 - 6114 (2007/10/03)
The asymmetric synthesis of (-)-(R)-pyrrolam A was achieved in three operations from N-Boc pyrrolidine via α-(N-carbamoyl)alkylcuprate vinylation reaction followed by N-Boc deprotection and cyclization. One-pot deprotection-cyclization procedures led to mixtures of pyrrolam A and its double bond isomers. These isomerization events could be circumvented by use of a two-step procedure. To guide aspects of the experiments, a series of computational energy evaluations and chemical shift predictions were performed with molecular mechanics, semiempirical, ab initio, and density functional methods. The relative stabilities of the double bond isomers, as estimated by experiment, challenged a number of computational methods, and only the MP2 model with its moderate degree of electron correlation came close to matching the experimental data. The MP2 method was further applied to an unusual aspect of the double bond migration between pyrrolam A and its isomer 9. The reaction (1 to 9) on neat samples is irreversible without racemization, and the alumina-mediated equilibration is accompanied by complete loss of enantiomeric excess. The source of the irreversibility was traced to asymmetric charge distribution in the intermediate dienolate anion. The analysis ultimately led to a semiquantitative sketch of the pyrrolam energy surface.
