Organocatalytic Asymmetric Conjugate Addition of Aldehydes to Nitroolefins: Identification of Catalytic Intermediates and the Stereoselectivity‐Determining Step by ESI‐MS

Bächle, Florian; Duschmalé, Jörg; Ebner, Christian; Pfaltz, Andreas; Wennemers, Helma

doi:10.1002/ange.201305338

Cited by 31 publications

(6 citation statements)

References 78 publications

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“…The Michael addition reaction of cyclohexanone to trans-β-nitrostyrene catalyzed by (1S,4S)-2-tosyl-2,5-diazabicyclo[2.2.1]heptane (2) and (R)-mandelic acid was monitored using high resolution mass spectrometry (MS-TOF), following the methodology previously reported by Wennemers et al [43] From this experiment, it was possible to obtain evidence of the involvement of enamine intermediate I, as well as iminium intermediate II prior to the formation of product III. These observations suggest that the reaction mechanism illustrated in Scheme 2 may be plausible.…”

Section: Resultsmentioning

confidence: 99%

Use of (R)-Mandelic Acid as Chiral Co-Catalyst in the Michael Addition Reaction Organocatalyzed by (1S,4S)-2-Tosyl-2,5-diazabicyclo[2.2.1]heptane under Solvent-Free Conditions

Avila‐Ortiz

López-Ortíz

Vega‐Peñaloza

et al. 2015

Asymmetric Catalysis

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This article describes a study on the Michael addition reaction of cyclohexanone to nitroolefins catalyzed by the chiral secondary amine (1S,4S)-2-tosyl-2,5-diazabicyclo[2.2.1]heptane. Reactions were carried out under solvent-free conditions to make them more environmentally friendly. Initially, the observed diastereoand enantioselectivities were moderate to good, but were significantly improved by lowering the reaction temperature. Furthermore, a variety of chiral acids were also tested as co-catalysts in both of their enantiomeric forms, which revealed that (R)-mandelic acid affords excellent results in terms of yield and stereoselectivity. Monitoring the reaction by MS-TOF allowed for the detection of key reaction intermediates, and a reasonable reaction mechanism in which both catalysts are involved is proposed.

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Section: Resultsmentioning

confidence: 99%

Use of (R)-Mandelic Acid as Chiral Co-Catalyst in the Michael Addition Reaction Organocatalyzed by (1S,4S)-2-Tosyl-2,5-diazabicyclo[2.2.1]heptane under Solvent-Free Conditions

Avila‐Ortiz

López-Ortíz

Vega‐Peñaloza

et al. 2015

Asymmetric Catalysis

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“…Mechanistic studies revealed that the conjugate addition reactions proceed via the formation of an enamine between the peptidic catalyst and the aldehydes and showed that the subsequent C-C bond formation with the nitroolefin is the stereoselectivity-determining and rate-limiting step in the catalytic cycle [31][32][33]. This insight allowed for further optimizing the reaction conditions and reducing the catalyst loading to as little as 0.1%, which is the lowest catalyst loading achieved in enamine catalysis to date [31].…”

Section: Peptide Catalysts With High Chemoselectivity and Reactivitymentioning

confidence: 91%

Asymmetric catalysis with short-chain peptides

Lewandowski

Wennemers

2014

Current Opinion in Chemical Biology

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“…Recently, much efforts has been made to identify novel peptide sequences to promote asymmetric transformations by using combinatorial screenings 7i,8. More precisely, Wennemers has identified the tripeptides H‐Pro‐Pro‐Asp‐NH 2 and H‐Pro‐Pro‐Glu‐NH 2 , respectively, as being efficient for enantioselective aldol reaction and Michael addition by means of an elegant split and mix combinatorial chemistry 7n–r,t…”

Section: Methodsmentioning

confidence: 99%

Prüfverfahren zur Bestimmung des Säurewiderstands von Betonen

König

Dehn

2015

Beton und Stahlbetonbau

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Im Rahmen einer Studie konnte ein Prüfverfahren zur Bewertung des Säurewiderstands von Betonen konzeptioniert werden, welches die säurespezifischen Reaktionsmechanismen sowie die Wechselwirkung zwischen einer sauren Flüssigkeit und einem alkalischen Beton berücksichtigt. Die Reproduzierbarkeit der durch das Prüfverfahren gewonnenen Ergebnisse konnte mittels umfangreicher experimenteller Untersuchungen für verschiedene Betone nachgewiesen werden. Nachfolgender Beitrag fasst die wesentlichsten Erkenntnisse zusammen und gibt zudem einen Vorschlag für ein mit dem Prüfverfahren zusammenhängendes Nachweiskonzept zur Bewertung des Säurewiderstands von Betonen. Test method to determine the acid resistance of concretes In the frame of a study, a test method for the evaluation of the acid resistance of concretes was developed which takes particularly the acid specific reaction mechanisms as well as the interaction between acidic liquid and alkaline concrete into account. The evidence of reproducibility of the results gained with the test method has been shown by means of extensive experimental investigations on different types of concrete. The following contribution summarizes the most significant findings and suggests a verification concept for the evaluation of the acid resistance of concretes related to the proposed test method.

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Organocatalytic Asymmetric Conjugate Addition of Aldehydes to Nitroolefins: Identification of Catalytic Intermediates and the Stereoselectivity‐Determining Step by ESI‐MS

Cited by 31 publications

References 78 publications

Use of (R)-Mandelic Acid as Chiral Co-Catalyst in the Michael Addition Reaction Organocatalyzed by (1S,4S)-2-Tosyl-2,5-diazabicyclo[2.2.1]heptane under Solvent-Free Conditions

Use of (R)-Mandelic Acid as Chiral Co-Catalyst in the Michael Addition Reaction Organocatalyzed by (1S,4S)-2-Tosyl-2,5-diazabicyclo[2.2.1]heptane under Solvent-Free Conditions

Asymmetric catalysis with short-chain peptides

Prüfverfahren zur Bestimmung des Säurewiderstands von Betonen

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