Selective Bromination of α-Chloro and α-Bromo Carboxylic Acid Derivatives

Shaw, J.P.; Tan, Eng Wui

doi:10.1021/jo960311l

Cited by 12 publications

(4 citation statements)

References 22 publications

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“…The reaction proceeds via an ionic mechanism. Shaw et al 783 selectively brominated α-chloro and α-bromo carboxylic acid derivatives. Bromination of the α-halo acid derivatives was carried out with NBS in refluxing CCl 4 , with irradiation from a 160 W mercury gas discharge lamp (Scheme 230).…”

Section: Aromatic Bromination Using Nbsmentioning

confidence: 99%

Use of Bromine and Bromo-Organic Compounds in Organic Synthesis

2016

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Bromination is one of the most important transformations in organic synthesis and can be carried out using bromine and many other bromo compounds. Use of molecular bromine in organic synthesis is well-known. However, due to the hazardous nature of bromine, enormous growth has been witnessed in the past several decades for the development of solid bromine carriers. This review outlines the use of bromine and different bromo-organic compounds in organic synthesis. The applications of bromine, a total of 107 bromo-organic compounds, 11 other brominating agents, and a few natural bromine sources were incorporated. The scope of these reagents for various organic transformations such as bromination, cohalogenation, oxidation, cyclization, ring-opening reactions, substitution, rearrangement, hydrolysis, catalysis, etc. has been described briefly to highlight important aspects of the bromo-organic compounds in organic synthesis.

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Section: Aromatic Bromination Using Nbsmentioning

confidence: 99%

Use of Bromine and Bromo-Organic Compounds in Organic Synthesis

2016

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“…Additionally, stereoselective bromination leads to enantiopure a,b-dihalogenated compounds. [36,37] Chiral a-halo esters have found application in the synthesis of biologically active compounds [38,39] and herbicides [40] as well as in natural-product synthesis, [41] whereas stereocontrolled nucleophilic substitution on enantiopure ahalo esters gives access to optically active N-, O-, and S-containing compounds. [42][43][44][45][46][47] Herein, we propose the concept of "supported substrate activation" as a tool to probe the reactivity of a,b-unsaturated carboxylic esters with ene-reductases and to test the influence of additional substituents on the C=C bond activation.…”

Section: Introductionmentioning

confidence: 99%

“…33 Asymmetric hydrogenation of alkenes is restricted to fluoro derivatives34, 35 due to reductive dehalogenation in the presence of reducing metal agents. Additionally, stereoselective bromination leads to enantiopure α,β‐dihalogenated compounds 36. 37 Chiral α‐halo esters have found application in the synthesis of biologically active compounds38, 39 and herbicides40 as well as in natural‐product synthesis,41 whereas stereocontrolled nucleophilic substitution on enantiopure α‐halo esters gives access to optically active N‐, O‐, and S‐containing compounds 42–47…”

Section: Introductionmentioning

confidence: 99%

A Substrate‐Driven Approach to Determine Reactivities of α,β‐Unsaturated Carboxylic Esters Towards Asymmetric Bioreduction

Tasnádi

Winkler

Clay

et al. 2012

Chemistry A European J

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The degree of C=C bond activation in the asymmetric bioreduction of α,β-unsaturated carboxylic esters by ene-reductases was studied, and general recommendations to render these "borderline-substrates" more reactive towards enzymatic reduction are proposed. The concept of "supported substrate activation" was developed. In general, an additional α-halogenated substituent proved to be beneficial for enzymatic activity, whereas β-alkyl or β-aryl substituents were detrimental for the reactivity of nonhalogenated substrates, and α-cyano groups showed little effect. The alcohol moiety of the ester functionality was found to have a strong influence on the reaction rate. Overall, activities were determined by both steric and electronic effects.

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“…Here, we report strong evidence of an enantioselective 1,2-chlorine atom migration governed by polar substituent effects. In previous work, we described experimental and theoretical studies on the stereoselective N -bromosuccinimide (NBS) radical bromination of α-chlorohydrocinnamic acid derivatives (for example, Figure ). The stereoselectivity was observed to be dependent upon the nature of the acid derivative and was partly attributed to the conformer distribution of the radical intermediate.…”

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confidence: 99%

A Polar Effects Controlled Enantioselective 1,2-Chlorine Atom Migration via a Chlorine-Bridged Radical Intermediate

2002

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An enantioselective 1,2-chlorine atom migration was observed in the tributyltin hydride reduction of various dihalogenated dihydrocinnamic acid derivatives. It is proposed that the reduction involves the formation of a chlorine-bridged radical intermediate, followed by hydrogen atom transfer to either the beta- or the alpha-carbon. The product distribution is affected by electron-withdrawing groups in that hydrogen atom transfer to the proximate carbon is favored. Presumably, this is due to the transition state of the hydrogen delivery step being electron rich, due to the relatively electropositive tin radical. These results demonstrate a 1,2-chlorine atom migration reaction governed by polar effects.

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Selective Bromination of α-Chloro and α-Bromo Carboxylic Acid Derivatives

Cited by 12 publications

References 22 publications

Use of Bromine and Bromo-Organic Compounds in Organic Synthesis

Use of Bromine and Bromo-Organic Compounds in Organic Synthesis

A Substrate‐Driven Approach to Determine Reactivities of α,β‐Unsaturated Carboxylic Esters Towards Asymmetric Bioreduction

A Polar Effects Controlled Enantioselective 1,2-Chlorine Atom Migration via a Chlorine-Bridged Radical Intermediate

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