Mechanisms of Elimination Reactions. XXI. The Alkaline Dehydrochlorination of meso- and dl-Stilbene Dichlorides<sup>1</sup>

Cristol, Stanley J.; Bly, Robert S.

doi:10.1021/ja01486a032

Cited by 20 publications

(7 citation statements)

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“…[70] This has obvious implications for both reaction stereoselectivity and -specificity,w ith weakly bridged haliranium ions typically resulting in non-stereospecific dihalogenations to give anti/syn dihalide mixtures. [23] In the dichlorinations of some conjugated alkene substrates,f or example,i mperfect anti-diastereoselectivity or even predominant syn-addition can occur, [71] as in the reaction of (E)-stilbene 28 with molecular Cl 2 (Scheme 32). [71d] However,the interpretation of such results as being the sole consequence of b-chloro carbocations should be made with caution, as the precise reaction conditions and concentrations have not always been specified, and the work of Poutsma has shown that certain .…”

Section: Type Id Ihalogenationmentioning

confidence: 99%

Catalytic, Stereoselective Dihalogenation of Alkenes: Challenges and Opportunities

2015

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Although recent years have witnessed significant advances in the development of catalytic, enantioselective halofunctionalizations of alkenes, the related dihalogenation of olefins to afford enantioenriched vicinal dihalide products remains comparatively underdeveloped. However, the growing number of complex natural products bearing halogen atoms at stereogenic centers has underscored this critical gap in the synthetic chemist's arsenal. This Review highlights the selectivity challenges inherent in the design of enantioselective dihalogenation processes, and formulates a mechanism-based classification of alkene dihalogenations, including those that may circumvent the "classical" haliranium (or alkene-dihalogen π-complex) intermediates. A variety of metal and main group halide reagents that have been used for the dichlorination or dibromination of alkenes are discussed, and the proposed mechanisms of these transformations are critically evaluated. AbstractCatalysis of alkene dihalogenation , under different activation modes, with control over both the absolute and relative stereochemical course of dihalogen addition, is one of the most vexing problems in stereoselective synthesis. Dihalogenations that circumvent the "classical" haliranium (or alkene-dihalogen π complex) intermediates provide new and exciting opportunities for catalysis, potentially having broader implications for the design of stereoselective alkene difunctionalizations.

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Section: Type Id Ihalogenationmentioning

confidence: 99%

Catalytic, Stereoselective Dihalogenation of Alkenes: Challenges and Opportunities

2015

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“…Dies wirkt sich offensichtlich auf die Stereoselektivität und ‐spezifität der Reaktion aus, wobei schwach verbrückte Haliraniumionen üblicherweise Dihalogenierungen ohne Stereospezifität zur Folge haben und zu anti / syn ‐Gemischen der Dihalogenide führen 23. Beispielsweise kann die Dichlorierung einiger konjugierter Alkensubstrate mit reduzierter anti ‐Diastereoselektivität ablaufen, oder es kann sogar die syn ‐Addition bevorzugt sein,71 wie in der Reaktion von ( E )‐Stilben 28 mit molekularem Cl 2 (Schema ) 71d. Allerdings sollte man vorsichtig sein, solche Ergebnisse dahingehend zu interpretieren, dass sie einzig die Folge der Bildung von β‐Chlorcarbokationen sind, da die exakten Reaktionsbedingungen und Konzentrationen nicht immer genau angegeben wurden.…”

Section: Mechanistische Klassifizierung Der Dihalogenierung Von Alunclassified

Katalytische stereoselektive Dihalogenierung von Alkenen: Herausforderungen und Chancen

2015

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Während in den letzten Jahren signifikante Fortschritte bei der Entwicklung katalytischer, enantioselektiver Halogenfunktionalisierungen von Alkenen erzielt wurden, ist die verwandte Dihalogenierung von Olefinen zur Bildung enantiomerenangereicherter vicinaler dihalogenierter Produkte vergleichsweise unterentwickelt. Allerdings verweist die steigende Anzahl komplexer Naturstoffe mit Halogenatomen an stereogenen Zentren deutlich auf diese Lücke im Arsenal der Synthesechemie. Dieser Aufsatz behandelt die Herausforderungen bei der gezielten Entwicklung enantioselektiver Dihalogenierungsprozesse und formuliert eine mechanismusbasierte Klassifizierung der Dihalogenierung von Alkenen, einschließlich solcher, welche die “klassischen” Haliranium‐Intermediate (oder Alkendihalogen‐π‐Komplexe) umgehen können. Die Anwendung zahlreicher Metall‐ und Hauptgruppenhalogenide als Reagentien zur Dichlorierung oder Dibromierung von Alkenen wird diskutiert, und die vorgeschlagenen Mechanismen dieser Transformationen werden kritisch beurteilt.

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“…Although it was recognized by Ingold as early as 1927 (1) that bimolecular p-elimination reactions need not be fully synchronous processes, it has only been in recent years that the concept of a continuous spectrum of E2 reactions differing in the relative extent of C,-X and Cp-H bond rupture in the transition state has been invoked to account for observed phenomena (2)(3)(4)(5)(6)(7)(8)(9)(10)(11)(12)(13). The various factors, structural and environmental, which can be expected to influence the nature of the tf-ansition state have been discussed very recently by Bunnett (14), who, along with others (15,16), has critically examined the limited number of tests now available for assessing the position of any particular elimination in the spectrum of E2 mechanisms.…”

Section: Introductionmentioning

confidence: 99%

Isotope Effect Studies on Elimination Reactions: Iii. Nitrogen Isotope Effects in the E2 Reaction of Ethyltrimethyl-Ammonium and 2-Phenylethyltrimethylammonium Ions

Ayrey¹,

Bourns²,

Vyas³

1963

Can. J. Chem.

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Nitrogen isotope effects have been determined for the E 2 reaction of two quaternary ammonium salts with ethoxide ion in ethanol. Ethyltrimethylammonium iodide gave k14/k1j values of 1.017 a t 60" and 1.015 a t 95', while 2-phenylethyltrimethylarnmonium bromide gave 1.012 a t 40' and 1.009 a t 60'. These results and the p-deuterium isotope effects reported by others have been interpreted in terms of the relative extent of C,-Kt and Cp-H bond weakening in the transition states of the two reactions.

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Mechanisms of Elimination Reactions. XXI. The Alkaline Dehydrochlorination of meso- and dl-Stilbene Dichlorides¹

Cited by 20 publications

References 1 publication

Catalytic, Stereoselective Dihalogenation of Alkenes: Challenges and Opportunities

Catalytic, Stereoselective Dihalogenation of Alkenes: Challenges and Opportunities

Katalytische stereoselektive Dihalogenierung von Alkenen: Herausforderungen und Chancen

Isotope Effect Studies on Elimination Reactions: Iii. Nitrogen Isotope Effects in the E2 Reaction of Ethyltrimethyl-Ammonium and 2-Phenylethyltrimethylammonium Ions

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Mechanisms of Elimination Reactions. XXI. The Alkaline Dehydrochlorination of meso- and dl-Stilbene Dichlorides1

Cited by 20 publications

References 1 publication

Catalytic, Stereoselective Dihalogenation of Alkenes: Challenges and Opportunities

Catalytic, Stereoselective Dihalogenation of Alkenes: Challenges and Opportunities

Katalytische stereoselektive Dihalogenierung von Alkenen: Herausforderungen und Chancen

Isotope Effect Studies on Elimination Reactions: Iii. Nitrogen Isotope Effects in the E2 Reaction of Ethyltrimethyl-Ammonium and 2-Phenylethyltrimethylammonium Ions

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Mechanisms of Elimination Reactions. XXI. The Alkaline Dehydrochlorination of meso- and dl-Stilbene Dichlorides¹