Synthesis and cycloaddition reactions of acetylenic iminium compounds

Baum, Jonathan S.; Viehe, H. G.

doi:10.1021/jo00864a001

Cited by 57 publications

(28 citation statements)

References 9 publications

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“…In Table , a comparison is made for Diels‐Alder reactions of cyclopentadiene and anthracene with terminal acetylenic iminium or amidium salts and other common electron‐deficient acetylenic and olefinic dienophiles , . It can be seen that the acetylenic iminium salts are extremely reactive dienophiles, even more reactive than corresponding amidium salts.…”

Section: Resultsmentioning

confidence: 99%

“…The isolation and characterization of acetylenic iminium salts I featuring a terminal C,C‐triple bond has not been reported so far. The closest analogy is represented by the terminal acetylenic amidium salts II ‐BF 4 , reported by Baum and Viehe , and an N , N , N′ , N′ ‐tetramethyl‐propiolamidinium tetraphenylborate III , reported by our group . While iminium ions II clearly exhibited an enhanced reactivity as dienophiles and dipolarophiles compared to propiolaldehyde, the amidinium ion salt gave merely a somewhat better performance in the [3+2] cycloaddition with C ‐phenyl‐ N ‐methyl nitrone or benzyl azide, and it underwent the Diels‐Alder reaction with common dienophiles only under forcing conditions (with cyclopentadiene) or not at all.…”

Section: Introductionmentioning

confidence: 99%

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Terminal Acetylenic Iminium Salts – Synthesis and Reactivity

et al. 2018

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Various types of terminal acetylenic iminium triflates (propyne iminium salts) featuring a ketiminium or an aldiminium group have been prepared for the first time by protiodesilylation of the corresponding trimethylsilyl‐substituted acetylenic iminium salts using triflic acid and catalytic silver(I) triflate. The high reactivity of the terminal C,C‐triple bond is documented herein by the facile Michael addition of nucleophiles and the exceptionally high dienophilic reactivity in Diels‐Alder reactions.

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Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Terminal Acetylenic Iminium Salts – Synthesis and Reactivity

et al. 2018

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“…[27] Ein weiteres meisterhaftes Beispiel ist die Verwendung von (S)-Phenylalanin zur enantioselektiven Cyclodehydrierung eines Trions in der Synthese von Estron durch Danishefsky und Cain. [28] Das Potenzial von Iminiumion-Intermediaten für die enantioselektive Synthese zeigt sich in den wegweisenden Arbeiten von Baum und Viehe [29] sowie Jung et al [30] Genauso kann die a-Funktionalisierung von a,bungesättigten Aldehyden unter Verwendung eines chiralen Amins durch Yamada et al [31] als Vorreiter der Dienaminaktivierung gesehen werden, [32] und die Perfluoralkylierung von Kitazume und Ishikawa [33] scheint ein entfernter Verwandter der modernen Photoredoxchemie zu sein. [34] Ein vollständigeres Resümee der Geschichte und Entstehung der Organokatalyse kann an anderer Stelle gefunden werden.…”

Section: Historischer üBerblick üBer Die Organokatalyseunclassified

Dekonstruktion kovalenter Organokatalyse

Holland

Gilmour

2015

Angewandte Chemie

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Die moderne Organokatalyse hat sich zu einem essenziellen Bestandteil der gegenwärtigen organischen Synthese entwickelt. Einer der markantesten Aspekte organokatalytischer Prozesse ist die biomimetische Weise, in welcher der Katalysator das Substrat bindet, wobei oftmals kovalent gebundene Intermediate in einer Art gebildet werden, die an enzymatische Katalyse erinnert. In der Tat geht der Prozess der Intermolekularisierung oft mit Konformationsänderungen des Katalysatorgerüsts einher, was die Analogie zu biologischen Systemen weiter verstärkt. Die Isolierung und Untersuchung dieser Katalyse‐Intermediate vereinfachen die rasche Erstellung von Konformations‐ und Reaktivitätsprofilen, welche die Entwicklung organokatalytischer Reaktionen erleichtern und/oder Reaktionsresultate erklären können. Die Dekonstruktion von kovalent gebundenen Organokatalyse‐Intermediaten als Designstrategie gewinnt an Bedeutung, motiviert durch die Fortschritte aus der Untersuchung von Reaktionsintermediaten in der mechanistischen metallorganischen und Enzymkatalyse.

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“…In our original communication on the alcoholysis of amides (5), we postulated that acidic hydrolysis of the acyclic orthoester 24 was the leading pathway to yield the observed esters (Scheme 5). Conversely, there are numerous reported examples of hydrolysis of O-alkyliminium ethers such as 23 under acidic (25)(26)(27)(28)(29)(30)(31) or basic conditions (32)(33)(34)(35)(36)(37)(38)(39). In an effort to identify which of these two intermediates was formed, we decided to monitor the alcoholysis of 1-pyridylimidoyl triflate 6 with ethanol-d 6 by 1 H NMR (Fig.…”

Section: General Mechanisms For the Amide Activation Process And Convmentioning

confidence: 99%

Spectroscopic studies of the electrophilic activation of amides with triflic anhydride and pyridine

Charette¹,

Grenon²

2001

Can. J. Chem.

147

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The reaction of amides with trifluoromethanesulfonic (triflic) anhydride in the presence of pyridine was thoroughly investigated by NMR spectroscopic techniques. Different pyridinium intermediates were generated from secondary amides, tertiary amides with enolizable protons, and tertiary amides lacking enolizable protons. It was found that the actual triflating reagent is N-(trifluoromethylsulfonyl)pyridinium triflate 11 which is formed by the initial reaction of triflic anhydride with pyridine. The alcoholysis of these intermediates yields O-alkyliminium ethers which can then be easily hydrolyzed under mild acidic conditions to the corresponding esters.Résumé : La réaction entre un amide et l'anhydride trifluorométhanesulfonique (triflique) en présence de pyridine a été examinée minutieusement à l'aide de nombreuses techniques de spectroscopie RMN. Des intermédiaires pyridiniums différents ont été générés à partir d'amides secondaires, d'amides tertiaires avec des protons énolisables et d'amides tertiaires ne possédant pas de protons énolisables. Nous avons aussi démontré que le triflate de N-(trifluorométhylsulfonyl)pyridinium 11, formé lors de la réaction initiale entre l'anhydride triflique et la pyridine, est le véritable agent de triflation. L'alcoolyse de ces intermédiaires donne des éthers O-alkyliminiums qui peuvent être facilement hydrolysés dans des conditions légèrement acides aux esters correspondants. Charette and Grenon 1695Scheme 1. Functional group interconversion involving amides as starting materials.Scheme 2. Postulated intermediates formed in the reaction of amides with triflic anhydride.

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Synthesis and cycloaddition reactions of acetylenic iminium compounds

Cited by 57 publications

References 9 publications

Terminal Acetylenic Iminium Salts – Synthesis and Reactivity

Terminal Acetylenic Iminium Salts – Synthesis and Reactivity

Dekonstruktion kovalenter Organokatalyse

Spectroscopic studies of the electrophilic activation of amides with triflic anhydride and pyridine

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