- Biomimetic approach to Galbulimina type I alkaloids
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On treatment with trifluoroacetic acid the tetraene precursor 23 underwent Boc deprotection, condensation and an iminium ion accelerated intramolecular Diels-Alder cycloaddition resulting in an iminium species 12, which was further converted into himbacin
- Tchabanenko, Kirill,Chesworth, Richard,Parker, Jeremy S.,Anand, Neel K.,Russell, Andrew T.,Adlington, Robert M.,Baldwin, Jack E.
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- An improved resolution of 2-methyl piperidine and its use in the synthesis of homochiral trans-2,6-dialkyl piperidines
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An efficient procedure for the resolution of 2-methylpiperidine is described. The enantiomers were used for a short and effective synthesis of the C2 symmetric piperidine, (+)-lupetidine and (+)-epidihydropinidine.
- Adamo, Mauro F. A.,Aggarwal, Varinder K.,Sage, Matthew A.
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- Biomimetic total synthesis of (+)-himbacine
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(Chemical Equation Presented) On treatment with trifluoroacetic acid butenolide 14 undergoes N-Boc deprotection and condensation followed by an iminium ion activated intramolecular Diels-Alder cycloaddition to give the (+)-himbacine precursor 11 on reduct
- Tchabanenko, Kirill,Adlington, Robert M.,Cowley, Andrew R.,Baldwin, Jack E.
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- Asymmetric deprotonation of N -boc piperidine: React IR monitoring and mechanistic aspects
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The high yielding asymmetric deprotonation trapping of N-Boc piperidine is successfully realized using s-BuLi and a (+)-sparteine surrogate. Monitoring of the lithiation by in situ React IR allowed the direct observation of a prelithiation complex.
- Stead, Darren,Carbone, Giorgio,O'Brien, Peter,Campos, Kevin R.,Coldham, Iain,Sanderson, Adam
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supporting information; experimental part
p. 7260 - 7261
(2010/07/13)
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- Asymmetrie substitutions of 2-lithiated N-boc-piperidine and N-boc-azepine by dynamic resolution
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Proton abstraction of N-tertbutoxycarbonyl-piperidine (N-Boc-piperidine) with sBuLi and TMEDA provides a racemic organolithium that can be resolved using a chiral ligand. The enantiomeric organolithiums can interconvert so that a dynamic resolution occurs. Two mechanisms for promoting enantioselectivity in the products are possible. Slow addition of an electrophile such as trimethylsilyl chloride allows dynamic resolution under kinetic control (DKR). This process occurs with high enantioselectivity and is successful by catalysis with substoichiometric chiral ligand (catalytic dynamic kinetic resolution). Alternatively, the two enantiomers of this organolithium can be resolved under thermodynamic control with good enantioselectivity (dynamic thermodynamic resolution, DTR). The best ligands found are based on chiral diamino-alkoxides. Using DTR, a variety of electrophiles can be used to provide an asymmetric synthesis of enantiomerically enriched 2-substituted piperidines, including (after Boc deprotection) the alkaloid (+)-ss-conhydrine. The chemistry was extended, albeit with lower yields, to the corresponding 2-substituted sevenmembered azepine ring derivatives.
- Coldham, Iain,Raimbault, Sophie,Whittaker, David T. E.,Chovatia, Praful T.,Leonori, Daniele,Patel, Jignesh J.,Sheikh, Nadeem S.
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experimental part
p. 4082 - 4090
(2010/07/10)
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- Synthesis of enantiomerically pure fire ant venom alkaloids: Solenopsins and isosolenopsins A, B and C
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(Chemical Equation Presented) Concise and efficient methods for the synthesis of enantiomers of fire ant venom alkaloids solenopsin and isosolenopsin A, B, and C are described. These syntheses are based on diastereoselective electrophilic substitution of enatiomerically-pure α-lithiated 2-alkylpiperidine.
- Bandara Herath,Dhammika Nanayakkara
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p. 129 - 136
(2008/09/20)
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- Dynamic kinetic and kinetic resolution of N-Boc-2-lithiopiperidine
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Asymmetric substitution of 2-lithiopiperidines can be achieved by dynamic resolution; the organolithium is formed as a racemic mixture by proton abstraction (or tin-lithium exchange) and is resolved in the presence of a chiral ligand. The Royal Society of
- Coldham, Iain,Patel, Jignesh J.,Raimbault, Sophie,Whittaker, David T. E.
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p. 4534 - 4536
(2008/09/16)
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- A new asymmetric synthesis of (S)-(+)-pipecoline and (S)-(+)- and (R)-(-)-coniine by reductive photocyclization of dienamides
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(S)-(+)-Pipecoline and both enantiomers of coniine were synthesized, in good yields, by a reductive photocyclization of chiral dienamides. Enantioselectivities of up to 75% were obtained. (C) 2000 Published by Elsevier Science Ltd.
- Bois,Gardette,Gramain
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p. 8769 - 8772
(2007/10/03)
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- Total synthesis of (+)-himbacine and (+)-himbeline
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Himbacine (1), a complex piperidine alkaloid isolated from the bark of Australian magnolias, is a promising lead in Alzheimer's disease research due to its potent muscarinic receptor antagonist property. We have described here a highly efficient synthetic strategy that resulted in the total synthesis of himbacine (1) in about 10% overall yield and isohimbacine (1a), an unnatural isomer of himbacine, in 18% overall yield. The total synthesis of himbacine was initially approached using an intramolecular Diels-Alder reaction as the key step to generate intermediate 5 followed by a [3 + 2] cycloaddition with nitrone 4 to produce the isoxazolidine derivative 3. Methylation followed by catalytic reduction of 3 gave 12'-hydroxyhimbacine (20), which, upon dehydration, gave isohimbacine (1a) as the sole product. In an alternative approach, an all-encompassing intramolecular Diels-Alder reaction of an appropriately substituted tetraene derivative 31, which bears the entire latent carbon framework and functional group substitution of himbacine, gave the desired advanced tricyclic intermediate 33, which was readily converted to (+)-himbeline (2) and (+)-himbacine (1).
- Chackalamannil, Samuel,Davies, Robert J.,Wang, Yuguang,Asberom, Theodros,Doller, Dario,Wong, Jesse,Leone, Daria,McPhail, Andrew T.
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p. 1932 - 1940
(2007/10/03)
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- A practical preparation of (R)- and (S)-N-Boc-2-methylpiperidines
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The resolution of (±)-2-methylpiperidine using D- and L-tartaric acid followed by direct conversion of the intermediate tartrate salts to (R) and (S)-N-Boc-2-methylpiperidine is described. Also described is an NMR protocol for assessing the optical purity of the intermediate tartrate salts as well as the free bases. The resolved enantiomers showed an ee of >98% based on NMR integration.
- Doller, Dario,Davies, Robert,Chackalamannil, Samuel
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p. 1275 - 1278
(2007/10/03)
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