- Scalable methodology for the catalytic, asymmetric α-bromination of acid chlorides
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The optimization of a practical, catalytic, asymmetric process for the α-bromination of acid chlorides to produce synthetically versatile, optically active α-bromoesters is reported. A range of products is produced in high enantioselectivity and moderate to good chemical yields with retention of both upon scale-up. The reactions herein are catalyzed by cinchona alkaloid derivatives, with the best performance achieved by the use of a proline cinchona alkaloid conjugate designed in a de novo fashion.
- Dogo-Isonagie, Cajetan,Bekele, Tefsit,France, Stefan,Wolfer, Jamison,Weatherwax, Anthony,Taggi, Andrew E.,Lectka, Thomas
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- Reactive Ketenes through a Carbonate/Amine Shuttle Deprotonation Strategy: Catalytic, Enantioselective α-Bromination of Acid Chlorides
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We have developed an efficient methodology for the generation of ketenes by employing a catalytic shuttle base and potassium carbonate as a stoichiometric base. We have applied this technology to the catalytic, asymmetric α-bromination of acid chlorides.
- Hafez, Ahmed M.,Taggi, Andrew E.,Wack, Harald,Esterbrook, Julie,Lectka, Thomas
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- A mechanistic study on the catalytic, asymmetric α-bromination of acid chlorides
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The mechanism of the catalytic, asymmetric α-bromination of acid chlorides is probed through a series of crossover experiments, ion-pairing tests, and kinetic resolution studies to shed light on the factors that contribute to, and limit the production of, optically-active α-bromo esters. In order to understand better the observed sense of induction, as well as the high degree of enantiomeric excess exhibited by these products, extensive molecular modeling is employed on the relevant transition states. Finally, the usefulness of the α-bromo ester products is demonstrated by their simple derivatization into chiral epoxides. Wiley-VCH Verlag GmbH & Co. KGaA, 2007.
- Dogo-Isonagie, Cajetan,Bekele, Tefsit,France, Stefan,Wolfer, Jamison,Weatherwax, Anthony,Taggi, Andrew E.,Paull, Daniel H.,Dudding, Travis,Lectka, Thomas
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- Synthesis of bromoalkenes and alkylidene dibromides by reactions of carbonyl compounds with 2,4,4,6-tetrabromo-2,5-cyclohexadienone in the presence of triphenylphosphine
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Reactions of aliphatic and aromatic aldehydes with the 2,4,4,6-tetrabromo-2,5-cyclohexadienone-triphenylphosphine complex result in formation of the corresponding geminal dibromides. Ketones react with the same complex to give vinyl bromides.
- Matveeva,Feshin,Zefirov
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- Peptide-Catalyzed Fragment Couplings that Form Axially Chiral Non-C2-Symmetric Biaryls
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We have demonstrated that small, modular, tetrameric peptides featuring the Lewis-basic residue β-dimethylaminoalanine (Dmaa) are capable of atroposelectively coupling naphthols and ester-bearing quinones to yield non-C2-symmetric BINOL-type scaffolds with good yields and enantioselectivity. The study culminates in the asymmetric synthesis of backbone-substituted scaffolds similar to 3,3′-disubstituted BINOLs, such as (R)-TRIP, with good (94:6 e.r.) to excellent (>99.9:0.1 e.r.) enantioselectivity after recrystallization, and a diastereoselective net arylation of the minimally modified nonsteroidal anti-inflammatory drug (NSAID) naproxen.
- Coombs, Gavin,Sak, Marcus H.,Miller, Scott J.
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supporting information
p. 2875 - 2880
(2020/01/24)
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- Electronic, infrared, mass spectrometry and thermal studies on the reaction of 2-amino-6-methylpyridine with π-acceptors
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The spectrophotometric characteristics of the solid charge-transfer molecular complexes (CT) formed in the reaction of the electron donor 2-amino-6-methylpyridine (2A6MPy) with the π-acceptors tetracyanoethylene (TCNE), 2,3-dichloro-5,6-dicyano-1,4-benzoq
- Madrahimov, Sherzod,Mostafa, Adel,Yempally, Veeranna,Fadlallah, Joelle,AlQaradawi, Siham Y.
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- Studies directed toward total synthesis of rhodocomatulins: A regioselective synthesis of brominated hydroxyanthraquinones by anionic annulations
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In this work, brominated hydroxyanthraquinones, which are the core structural motif of naturally occurring bromorhodocomatulins, were successfully synthesized using Hauser annulation reaction as the key step. When brominated Michael acceptors (brominated p-quinone monoketals) and cyanophthalides or bromocyanophthalides (Hauser donors) were reacted under the annulation conditions, brominated anthraquinones were obtained with 81–87% yields for four examples. On acidic quenching, products were obtained as solid which were separated by filtration and purified by recrystallization in acetone. No chromatography was required.
- Sk, Md Raja,Chakraborty, Soumen,Mal, Dipakranjan
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p. 309 - 317
(2018/02/09)
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- An efficient regioselective bromination protocol of activated coumarins using 2,4,4,6-tetrabromo-2,5-cyclohexadienone
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2,4,4,6-Tetrabromo-2,5-cyclohexadienone mediated bromination of a wide assortment of activated coumarins in acetonitrile has been accomplished with high regioselectivity and good to excellent yields. The selectivity and efficiency of bromination were found to be markedly dependent on electronic factors, particularly degree of electron withdrawal from electron-releasing 7-oxygenated substituents to the C-3 position of the α-pyrone moiety by vinylogous resonance and the presence of nucleophilic additives such as water and tetra-n-butylammonium bromide in the reaction medium. The sole by-product of the reaction was converted back to the reagent by oxidation with KBr-KBrO 3, which was recycled three times without significant loss of efficiency.
- Ganguly, Nemai C.,Nayek, Subhasis,Chandra, Sumanta
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supporting information
p. 1155 - 1159
(2013/11/06)
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- 1-Benzyl-4-aza-1-azoniabicyclo[2.2.2]octane tribromide as a regenerable and useful reagent for bromination of phenols under mild conditions
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1-Benzyl-4-aza-1-azoniabicyclo[2.2.2]octane tribromide has been examined over several phenolic compounds under mild conditions. The reaction gives brominated phenols in good to excellent yields. Straightforward work-up of the reaction yields pure products in several cases.
- Hajipour, Abdol R.,Pourmousavi, Seied A.,Ruoho, Arnold E.
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p. 796 - 800
(2007/10/03)
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- Triphenylphosphine-2,4,4,6-tetrabromo-2,5-cyclohexadienone complex as a reagent for preparation of carboxylic acid bromides
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Triphenylphosphine-2,4,4,6-tetrabromo-2,5-cyclohexadienone complex was successfully used as a new reagent for the synthesis of carboxylic acid bromides which were isolated as individual substances or were identified by conversion into the corresponding anilides. The reaction is chemoselective, and it can be applied to polyfunctional compounds, e.g., hydroxy acids.
- Matveeva,Podrugina,Sandakova,Zefirov
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p. 1469 - 1472
(2007/10/03)
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- PROCESS FOR PREPARING 2,4,46-TETRABROMO-2,5-CYCLOYHEXADIENONE
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A highly pure 2,4,4,6-tetrabromo-2,5-cyclohexadienone has been prepared in a single pot, eco-friendly procedure in yields of 91-94% from phenol. In this method, a mixture of alkali/alkaline earth metal bromide and alkali/alkaline earth metal bromate was employed as brominating agent in place of corrosive liquid bromine. The reaction between phenol and the brominating reagent was initiated by the action of a mineral acid or moderately strong organic acid. The crude product was further characterized by standard analytical and spectroscopic methods.
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- PROCESS FOR PREPARING 2,4,4,6-TETRABROMO-2,5-CYCLOHEXADIENONE
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A highly pure 2,4,4,6-tetrabromo-2,5-cyclohexadienone has been prepared in a single pot, eco-friendly procedure in yields of 91-94 % from phenol. In this method, a mixture of alkali/alkaline earth metal bromide and alkali/alkaline earth metal bromate was employed as brominating agent in place of corrosive liquid bromine. The reaction between phenol and the brominating reagent was initiated by the action of a mineral acid or moderately strong organic acid. The crude product was further characterized by standard analytical and spectroscopic methods.
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- Determination of phenol and resorcinol using 1,3-dibromo-5,5-dimethylhydantoin (DBH) analogous to the Koppeschaar reaction: Analytical methods of pharmacopoeias with DBH in respect to environmental and economical concern, part 6
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PH. EUR. 1997 determines phenol and resorcinol according to the Koppeschaar reaction using hepatotoxic and environmentally hazardous chloroform. Chlorinated hydrocarbons are not required when applying 1,3-dibromo-5,5-dimethylhydantoin (DBH). The reaction time for phenol can be reduced from 45 to 5 min. Blind values according to PH. EUR. 1997 result a systematic error of about - 1.8%.
- Hilp
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p. 777 - 779
(2007/10/03)
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