Stereochemical and base species dichotomies in olefin-forming E2 eliminations

Bartsch, Richard A.; Závada, Jiřı́

doi:10.1021/cr60328a001

Cited by 109 publications

(49 citation statements)

References 56 publications

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“…The HCl pair involved in the reaction is forced to adopt the 1,2-biaxial position in the enzyme active site. The requirement for the presence of a 1,2-biaxial HCl pair in the substrate molecules, the geometry of the active site as well as the kinetic measurements, indicate an E 2 -like dehydrochlorination mechanism (27). We propose that His-73 acts as the base and attacks the hydrogen atom on C3, resulting in breaking of the C3-H bond based on the analogous role of catalytic histidine in the scytalone dehydratase (13).…”

Section: Corresponds To the Enantiomorphic Pair 13(r)4(s)5 (S)6(rmentioning

confidence: 89%

Reaction Mechanism and Stereochemistry of γ-Hexachlorocyclohexane Dehydrochlorinase LinA

Trantı́rek

Hynková

Nagata

et al. 2001

Journal of Biological Chemistry

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␥-Hexachlorocyclohexane dehydrochlorinase (LinA) catalyzes the initial steps in the biotransformation of the important insecticide ␥-hexachlorocyclohexane (␥-HCH) by the soil bacterium Sphingomonas paucimobilis UT26. Stereochemical analysis of the reaction products formed during conversion of ␥-HCH by LinA was investigated by GC-MS, NMR, CD, and molecular modeling. The NMR spectra of 1,3,4,5,6-pentachlorocyclohexene (PCCH) produced from ␥-HCH using either enzymatic dehydrochlorination or alkaline dehydrochlorination were compared and found to be identical. Both enantiomers present in the racemate of synthetic ␥-PCCH were converted by LinA, each at a different rate.

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Section: Corresponds To the Enantiomorphic Pair 13(r)4(s)5 (S)6(rmentioning

confidence: 89%

Reaction Mechanism and Stereochemistry of γ-Hexachlorocyclohexane Dehydrochlorinase LinA

Trantı́rek

Hynková

Nagata

et al. 2001

Journal of Biological Chemistry

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“…1,4,8,26 Similarly, the complementary syn eliminations have also been studied. 1,4,26 The results of these studies reveal that the anti-elimination is more facile and proceeds through the transition state with less carbanionic character and smaller extents of C α −H bond cleavage than the corresponding syn-elimination reactions. In contrast, little was known about the differences between the syn-and anti-eliminations forming carbon-nitrogen triple bonds.…”

Section: Base-promoted Nitrile-forming Eliminations From (E)-and (Z)-mentioning

confidence: 99%

“…[1][2][3][4][5][6][7] The results of the structure-reactivity relationships studies have led to a qualitative understanding of the relationship between the reactant structure and the transition state structure. One of the most important achievements from these studies is the development of the More-O'Ferrall-Jencks energy diagram, which has become a useful tool for the interpretation of not only elimination reactions, but also substitution reactions and the reactions of carbonyl compounds, and found its way in advanced organic chemistry textbooks.…”

Section: Introductionmentioning

confidence: 99%

Base-promoted elimination reactions of (E)- and (Z)-arylaldehyde O-benzoyloximes. Effects of stereochemistry, β-aryl group and base-solvent on the nitrile-forming transition states

Pyun¹,

Cho²

2010

Arkivoc

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This account is dedicated to Professor Richardrate of anti-elimination was 36,000-fold faster than that of syn-elimination. The change of the β-aryl group from Ph to thienyl to furyl shifted the E2 transition state slightly towards product-like. When (E)-2,4-dinitrobenzaldehyde O-benzoyloxime was employed as the reactant and R 1 R 2 NH/R 1 R 2 NH 2 + in 70mol% MeCN(aq) was used as the base-solvent, the (E1cb) irr was observed.

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“…It is seen that both the rate constant k, and the magnitude of (k"/kD), initially increase from their values at "low" base concentration, when tertbutoxide concentration is increased, and level off at "high" base concentration. A possible rationalization of these results is that an increase in tert-butoxide concentration leads to a decrease in the amount of associated base species (which favours syn-elimination) and an increase in the concentration of multiple ions such as negatively charged ion triplets, (RO-),Mt, which may be considered as a free base (38). The bulky triple ion would presumably favour anti-elimination, for steric reasons, and a normal isotope effect and an increased rate of reaction would be observed because the triple ion is a stronger base than the associated species.…”

Section: T-buohmentioning

confidence: 99%

Secondary α-deuterium kinetic isotope effects for the E2 reaction of the 2-phenylethyl halides with tert-butoxide ion in tert-butyl alcohol

Smith¹,

Rangappa²,

Westaway³

1985

Can. J. Chem.

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PETER JAMES SMITH, KANCHUGARAKOPPAL S. RANGAPPA, and KENNETH CHARLES WESTAWAY. Can. J. Chem. 63, 100 (1985).Secondary a-deuterium kinetic isotope effects have been determined for the elimination reactions of 2-phenylethyl halides with tert-butoxide in tert-butyl alcohol at 40°C in the presence and absence of the crown ether 18C6. The second-order rate constant k, and the normal (kt'/kD), effect remained constant when the tert-butoxide concentration was varied for reaction of the iodo and bromo compounds. However, both the magnitude of k, and the secondary a-deuterium isotope effect were significantly dependent on [t-BuO-] when chlorine and fluorine are the leaving groups. It is noteworthy that (kH/k"),, is inverse for the reaction of both the chloro and fluoro compounds at "low" base concentrations and normal at "high" base concentrations. These results are discussed in terms of both syn-and anti-elimination pathways promoted by various associated and dissociated base species. It is suggested that the (kH/k"),, effect may be useful as a criterion for determining the stereochemistry of E2 elimination reactions.PETER JAMES SMITH, KANCHUGARAKOPPAL S. RANGAPPA et KENNETH CHARLES WESTAWAY. Can. J . Chem. 63, 100 (1985). Operant 3 40°C et en prtsence ou en I'absence de I'tther couronne 18C6, on a dttermink les effets isotopiques cinttiques secondaires des deuterium en a sur les reactions d'klimination des halogtnures de phenyl-2 Cthyles par la tert-butylate dans I'alcool tert-butylique. Dans les cas des compos6s iodCs ou bromCs, la constante de vitesse du deuxikme ordre (kZ) ainsi que I'effet normal (kH/k"),, demeurent constants lorsqu'on fait varier la concentration du tert-butylate. Toutefois, lorsque les groupes nucltofuges sont soit Ie fluor ou le chlore, ['amplitude de k2 ainsi que I'effet isotopique secondaire des deuterium en a varient d'une f a~o n importante avec la concentration de I'ion tert-butylate. I1 est notable que, pour les rkactions des composts fluorCs ou chlorCs 3 de "basses" concentrations de base, la valeur (kl'/k"),, est inverse; toutefois, h des concentrations "ClevCes" de base, cette valeur est normale. On discute de ces resultats en fonction de voies d'eliminations syn et anti qui sont PavorisCes par diverses cspkces basiques associCcs et dissocites. On suggkre que I'effet (kk'/k"),, pourrait etre un critkrc utile pour dCterminer la sttrtochimie des rCactions dlCliminations E2.[Traduit par le journal]The elimination reaction of the 2-arylethyl derivatives with different leaving groups Y, ArCH,CH,Y, has been extensively studied (1 -6) under a variety of solvent/base conditions. It has been established that the majority of the reactions proceed by way of the E2 mechanism following the anti pathway (5,7). Experimental studies (8)(9)(10)(11)(12)(13)(14) have demonstrated that the structures of the respective E2 transition states vary significantly in accord with theoretical re dictions (15)(16)(17)(18)(19)(20).The reaction of the 2-arylethyl quaternary ammonium ions with base has been-shown to h...

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Stereochemical and base species dichotomies in olefin-forming E2 eliminations

Cited by 109 publications

References 56 publications

Reaction Mechanism and Stereochemistry of γ-Hexachlorocyclohexane Dehydrochlorinase LinA

Reaction Mechanism and Stereochemistry of γ-Hexachlorocyclohexane Dehydrochlorinase LinA

Base-promoted elimination reactions of (E)- and (Z)-arylaldehyde O-benzoyloximes. Effects of stereochemistry, β-aryl group and base-solvent on the nitrile-forming transition states

Secondary α-deuterium kinetic isotope effects for the E2 reaction of the 2-phenylethyl halides with tert-butoxide ion in tert-butyl alcohol

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