- Diastereo- And Enantioselective Synthesis of Quaternary α-Amino Acid Precursors by Copper-Catalyzed Propargylation
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A diastereo- and enantioselective propargylic substitution reaction between propargylic carbonates and α-substituted nitroacetates catalyzed by a Cu-pybox complex is described. This method allows the preparation of a series of non-proteinogenic quaternary α-amino acid precursors featuring two contiguous stereogenic centers and a terminal alkyne moiety in high yields with good to excellent diastereo- and enantioselectivities in most cases. The propargylated adducts were elaborated into a diverse set of quaternary α-amino acid derivatives.
- Zhu, Qiongqiong,Meng, Beibei,Gu, Congzheng,Xu, Ye,Chen, Jie,Lei, Chuanhu,Wu, Xiaoyu
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supporting information
p. 9985 - 9989
(2019/12/24)
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- One-pot oxidative bromination – Esterification of aldehydes to 2-bromoesters using cerium (IV) ammonium nitrate and lithium bromide
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A two-step, one-pot reaction of aldehydes with the CAN/LiBr oxidation system under solvent-free conditions followed by the addition of methanol affords methyl α-bromocarboxylates. The oxidation of aldehydes with methanol using this system gives only methyl esters. A facile method, which does not require special equipment, was developed for the synthesis of 2-bromoesters from aliphatic aldehydes with carbon chain lengths of 5–10 atoms.
- Nikishin, Gennady I.,Kapustina, Nadezhda I.,Sokova, Lyubov L.,Bityukov, Oleg V.,Terent'ev, Alexander O.
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supporting information
p. 352 - 354
(2017/01/03)
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- GC separation of enantiomers of alkyl esters of 2-bromo substituted carboxylic acids enantiomers on 6-tbdms-2,3-di-alkyl- β- And γ-cyclodextrin stationary phases
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The gas chromatographic separation of enantiomers of 2-Br carboxylic acid derivatives was studied on four different 6-TBDMS-2,3-di-O-alkyl- β- and -γ-CD stationary phases. The differences in thermodynamic data {ΔH and -ΔS} for the 15 structurally related
- Spanik, Ivan,Kaceriakova, Darina,Krupcik, Jan,Armstrong, Daniel Wayne
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p. 279 - 285
(2014/06/09)
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- Site-selective aliphatic C-H bromination using N -bromoamides and visible light
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Transformations that selectively functionalize aliphatic C-H bonds hold significant promise to streamline complex molecule synthesis. Despite the potential for site-selective C-H functionalization, few intermolecular processes of preparative value exist. Herein, we report an approach to unactivated, aliphatic C-H bromination using readily available N-bromoamide reagents and visible light. These halogenations proceed in useful chemical yields, with substrate as the limiting reagent. The site selectivities of these radical-mediated C-H functionalizations are comparable (or superior) to the most selective intermolecular C-H functionalizations known. With the broad utility of alkyl bromides as synthetic intermediates, this convenient approach will find general use in chemical synthesis.
- Schmidt, Valerie A.,Quinn, Ryan K.,Brusoe, Andrew T.,Alexanian, Erik J.
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supporting information
p. 14389 - 14392
(2014/12/10)
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- Enoate reductase-mediated preparation of methyl (S)-2-bromobutanoate, a useful key intermediate for the synthesis of chiral active pharmaceutical ingredients
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Enoate reductases belonging to the Old Yellow Enzyme (OYE) family were employed to develop a biocatalysed approach to methyl (S)-2-bromobutanoate, a key intermediate for the introduction of a particular stereogenic unit into the molecular skeleton of a certain class of chiral drugs. Methyl (Z)-2-bromocrotonate afforded, respectively, (S)-2-bromobutanoic acid (ee = 97%) and methyl (S)-2-bromobutanoate (ee = 97%) by baker's yeast fermentation and by OYE1-3 biotransformations. The bioreductions of other methyl 2-haloalkenoates were also considered. It was observed that the (Z)- and (E)-diastereoisomers of α-bromo unsaturated esters afforded the same enantiomer of the corresponding reduced product.
- Brenna, Elisabetta,Gatti, Francesco G.,Manfredi, Alessia,Monti, Daniela,Parmeggiani, Fabio
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p. 262 - 268
(2012/06/18)
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- New free-radical halogenations of alkanes, catalysed by N-hydroxyphthalimide. Polar and enthalpic effects on the chemo- and regioselectivity
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Reactions of alkanes with different halogenating systems are compared in order to explore the reactivity of phthalimido-N-oxyl radical in hydrogen abstraction; the importance of polar effects is emphasised.
- Minisci, Francesco,Porta, Ombretta,Recupero, Francesco,Gambarotti, Cristian,Paganelli, Roberto,Pedulli, Gian Franco,Fontana, Francesca
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p. 1607 - 1609
(2007/10/03)
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- Electrooxidation of malonate and acetylacetate derivatives in the presence of halide ions
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β-Dicarbonyl compounds, such as dimethyl malonate derivatives and methyl acetoacetate derivatives, were electrooxidized in methanol in the presence of halogen ions to afford the corresponding dimethyl α-halomalonates and methyl α-halocarboxylates. Electrooxidation of bis(β-dimethoxycarbonyl) derivatives similarly afforded cyclic compounds and dihalides.
- Okimoto, Mitsuhiro,Takahashi, Yukio
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p. 2215 - 2219
(2007/10/03)
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- Enantioselective synthesis of α-bromo acid derivatives and bromohydrins from tartrate derived bromoacetals
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Bromination of the acetals 4 derived from aryl alkyl ketones, ArCOR, and (2R,3R)-tartaric acid results in bromoacetals 5 with 78-90% de. Hydrolysis of those compounds with Ar = 4-methoxyphenyl or 3-bromo-4-methoxyphenyl results, after recrystallisation, in α-bromoketones 8 with 66-98% ee which are shown to undergo the Baeyer-Villiger oxidation to α-bromoesters 9 with minimal racemisation, α-Bromoketone 8d is shown to undergo carbonyl reduction to threo-bromohydrin 15 with retention of stereochemistry.
- Boyes, Scott A.,Hewson, Alan T.
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p. 2759 - 2765
(2007/10/03)
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- Deacetylation of α-bromo-α-substituted-acetoacetates
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A new and efficient method for the deacetylation of α-bromo-α- substituted-acetoacetates to obtain α-bromoesters has been achieved by treatment with LiClO4/Et3N in ether at room temperature.
- Hu, Youhong,Bai, Donglu
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p. 2375 - 2376
(2007/10/03)
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- Thermally reticulated materials for non-linear optical applications
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This invention concerns new molecules with active, non-linear optical properties and which can be thermally reticulated (more precisely, these molecules include terminal functions which can be reticulated, attached to either side of the groups active in non-linear optics, which can be oriented under an electrical field). When reticulated and oriented under an electrical field, these materials are particularly stable and can be employed for industrial applications, using non-linear optics (electrooptical modulators, frequency doublers, etc.).
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