Highly enantioselective photodeconjugation of .alpha.,.beta.-unsaturated esters. Origin of the chiral discrimination

Piva, Olivier; Mortezaei, Reza; Hénin, Françoise; Мuzart, Jacques; Pete, Jean‐Pierre

doi:10.1021/ja00181a032

Cited by 91 publications

(23 citation statements)

References 3 publications

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“…Im gezeigten Beispiel mit Substrat 55 muss zuvor eine photochemische E/Z-Isomerisierung erfolgen, bevor das markierte Wasserstoffatom abstrahiert werden kann. [72] Als beste Protonenquelle stellte sich das gezeigte Norephedrin-Derivat 56 heraus, mit dem die Protonierung zu Produkt 57 enantioselektiv erfolgte. Die Reaktion ist katalytisch, weil im Protonierungsschritt gleichzeitig das DienolProton entfernt wird.…”

Section: Aminoalkoholeunclassified

Enantioselektive Katalyse photochemischer Reaktionen

et al. 2015

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Die Natur des angeregten Zustands macht die Entwicklung chiraler Katalysatoren für enantioselektive photochemische Reaktionen zu einer enormen Herausforderung. Die Absorption eines 400‐nm‐Photons entspricht einer Energieaufnahme von etwa 300 kJ mol−1. Es bedarf innovativer Konzepte, um in einem derart großen Abstand vom Grundzustand Reaktionspfade zu eröffnen, die gezielt zu einem Enantiomer einer chiralen Verbindung führen. Hier werden die beiden wesentlichen Vorgehensweisen für homogen katalysierte, enantioselektive Prozesse diskutiert. Im ersten Teil werden chirale Photokatalysatoren besprochen, die in den photochemischen Schlüsselschritt eingreifen und in diesem Schritt eine asymmetrische Induktion bewirken. Im zweiten Teil werden Reaktionen vorgestellt, in denen die photochemische Anregung durch einen achiralen Katalysator erfolgt und die asymmetrische Induktion durch einen zweiten chiralen Katalysator gewährleistet wird (duale Katalyse).

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Section: Aminoalkoholeunclassified

Enantioselektive Katalyse photochemischer Reaktionen

et al. 2015

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“…The photochemical in-situ-generation of dienols and their subsequent enantioselective organocatalytic tautomerization reactions in the presence of chiral b-amino alcohols was reported by Pete and co-workers [11][12][13][14][15][16][17][18]. For these photodeconjugation reactions, a,b-unsaturated esters and lactones serve as starting materials.…”

Section: Enantioselective Tautomerization Of Enols Generated In Situmentioning

confidence: 99%

“…For these photodeconjugation reactions, a,b-unsaturated esters and lactones serve as starting materials. Prerequisites for efficient reaction are rigorous exclusion of moisture, use of an apolar solvent, and a low reaction temperature of approximately À55 C [16][17][18]. The initial photochemical formation of the transient dienol 19, which involves intramolecular g-hydrogen bond abstraction of the allylic hydrogen and subsequent tautomerization in the presence of 10-15 mol% chiral bamino alcohol organocatalyst, gives the desired chiral carboxylates of type 20 bearing a stereogenic center in a-position, with enantioselectivity up to 91% ee [17].…”

Section: Enantioselective Tautomerization Of Enols Generated In Situmentioning

confidence: 99%

“…The course of the reaction in the presence of a b-amino alcohol as organocatalyst is shown in Scheme 9.5. In the presence of moisture and protic or basic solvents racemates are formed, because water and these types of solvent seem to compete with the chiral organocatalyst during the proton transfer step [16]. An example is shown in Scheme 9.5.…”

Section: Enantioselective Tautomerization Of Enols Generated In Situmentioning

confidence: 99%

“…A variety of chiral b-amino alcohols bearing, e.g., secondary or tertiary amine groups, have been tested as organocatalysts [16,17]. In particular, b-amino alcohols derived from (þ)-camphor, e.g.…”

Section: Enantioselective Tautomerization Of Enols Generated In Situmentioning

confidence: 99%

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Protonation of Enolates and Tautomerization of Enols

Berkessel

Gröger

2005

Asymmetric Organocatalysis

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Enantioselective protonation reactions are an important tool for synthesis of carbonyl compounds with a stereogenic carbon center in the a-position [1-4]. These compounds are useful building blocks as intermediates for, e.g., pharmaceuticals and fragrance compounds. For the latter, the industrial relevance of these reactions has already been demonstrated [3]. Most protonations are still based on the use of stoichiometric amounts of chiral auxiliary, although catalytic versions are gaining increasing importance. Metal enolates as indicated in Scheme 9.1, Eq. (a) or metal-free analogs as indicated in Scheme 9.1, Eq. (b) have been used as achiral precursors. When metal enolates are used a transition state is formed consisting of the chiral organic molecule and the metal. Thus, although this reaction starts with an organic molecule as ''catalyst'' it can be regarded as a transition metal complex-catalyzed synthesis in which the metal, surrounded by the chiral organic molecule as chiral ligand, plays an important role in the asymmetric induction process. Because this type of process seems to be more a metal complex-catalyzed reaction than a ''pure'' organocatalytic reaction, and taking into account that the subject of enantioselective protonation has already been reviewed extensively

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Reductive Aminations of Carbonyl Compounds with Borohydride and Borane Reducing Agents

2002

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Reductive amination is an important tool for synthetic organic chemists in the construction of carbon‐nitrogen bonds. This reaction, also termed reductive alkylation, involves condensation of an aldehyde or ketone with an amine in the presence of a reducing agent. A wide variety of substrates can be used including aliphatic and aromatic aldehydes and ketones, and even benzophenones. A range of amines from ammonia to aromatic amines, including those with electron‐withdrawing substituents, can be employed. For particularly sluggish reactions, such as those involving weakly electrophilic carbonyl groups, poorly nucleophilic amines, or sterically congested reactive centers, additives such as molecular sieves or Lewis acids are often useful. This chapter focuses on those conditions in which the carbonyl component, amine, and reducing reagent react in the same vessel. This review is restricted to reductive aminations using borohydride and borane reducing agents. This chapter concentrates on reductive amination chemistry mediated by borohydride and other boron‐containing reducing agents from 1971, the year when sodium cyanoborohydride was introduced, through the middle of 1999. In addition to reductive aminations of aldehyde and ketone substrates, reactions of related structures including acetals, aminals, ketals, carboxylic acids, nitriles, and dicarbonyls that form a nitrogen‐containing ring are reviewed. Intramolecular processes in which the substrate contains both the carbonyl and amine moieties are described. The intramolecular variant is a useful method for preparing cyclic amines. All of the various boron‐containing hydride sources in reductive aminations, including labeled metal hydrides, are reviewed. Instances of reductive aminations that failed are described. Applications of this method to a solid support in parallel synthesis in combinatorial chemistry as well as reductive aminations that proceed in tandem with a second reaction such as reductive lactamizations are discussed.

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Highly enantioselective photodeconjugation of .alpha.,.beta.-unsaturated esters. Origin of the chiral discrimination

Cited by 91 publications

References 3 publications

Enantioselektive Katalyse photochemischer Reaktionen

Enantioselektive Katalyse photochemischer Reaktionen

Protonation of Enolates and Tautomerization of Enols

Reductive Aminations of Carbonyl Compounds with Borohydride and Borane Reducing Agents

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