Enantioselective catalysis 98. Preparation of 9-amino(9-deoxy)cinchona alkaloids

Brunner, Henri; Bügler, Jürgen; Nuber, Bernhard

doi:10.1016/0957-4166(95)00215-b

Cited by 127 publications

(90 citation statements)

References 11 publications

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“…Dabei trifft man auf viele bekannte Gerüste, die sich bereits in nicht-photochemischen Arbeiten als privilegierte Strukturen herausgestellt haben, etwa die Pyrrolidine 61, [75] 64, [76] und 65, [77] die Imidazolidinone 62 [78] und 63, [79] sowie auf Chinin-Derivate wie 66 [80] (Abbildung 11). [82] Die intermediär erhaltenen a-Hydroperoxyaldehyde wurden sofort reduziert, und die entsprechenden Diole 67 wurden mit guter Enantioselektivität erhalten, wobei in der erwähnten Studie a-Methylprolin (61) als Katalysator verwendet wurde.…”

Section: Amineunclassified

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: Amineunclassified

Enantioselektive Katalyse photochemischer Reaktionen

et al. 2015

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“…The free amine 14 was prepared according to a slightly modified method of Brunner. 7,18 The methylated catalyst 12 was prepared by first forming the corresponding ethyl carbamate 15 from 14. The carbamate was subjected to LiAlH 4 reduction to attain the amine 16, which was subsequently condensed with 3,5-bis(trifluoromethyl)phenyl isothiocyanate.…”

Section: Takemotomentioning

confidence: 99%

Asymmetric organocatalytic Michael addition of Meldrum’s acid to nitroalkenes: probing the mechanism of bifunctional thiourea organocatalysts

Kataja¹,

Koskinen²

2010

Arkivoc

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“…On the other hand, a,b-unsaturated ketones 1 are sterically more demanding and electronically less active toward iminium formation with chiral amines. The activation of enones for asymmetric aza-Michael reactions by chiral secondary amines has not yet been reported.[9] Recently, 9-amino cinchona alkaloid 4, [10] in combination with various acids, has been shown to provide an effective catalyst system for the activation of enones 1 for various asymmetric conjugate addition reactions.[11] Presumably, compared to secondary amines, the sterically less-hindered primary amine in 4 reacts more readily with the ketone functionality in 1 to initiate the iminium catalysis. Thus, we reasoned that, while the primary amine activated the enone in the presence of acid by iminium catalysis, the quinuclidine motif of cinchona alkaloid 4, in either the free base (Scheme 1, mode a) or the protonated form (mode b), could bind to nitrogen nucleophiles, such as alkoxyamines, through hydrogen-bonding interactions, thereby activating the nitrogen nucleophile for nucleophilic …”

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confidence: 99%

Asymmetric Aza‐Michael Reactions of α,β‐Unsaturated Ketones with Bifunctional Organic Catalysts

Deng

2008

Angewandte Chemie

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Chiral amine motifs are present in numerous biologically active and therapeutically important molecules. Consequently chiral amines constitute one of the most important classes of chiral building blocks in organic synthesis. Accordingly, significant efforts have been devoted to the development of catalytic enantioselective transformations of inexpensive achiral precursors into optically active chiral amines. Alongside enantioselective additions to achiral imines, catalytic asymmetric conjugate additions with nitrogen nucleophiles (aza-Michael reactions) provide another fundamentally important approach toward optically active chiral amines. [1] Although much progress has been made recently in the development of asymmetric aza-Michael reactions with both chiral metallic [2][3][4] and organic catalysts, [5][6][7] highly enantioselective catalytic aza-Michael additions to simple a,b-unsaturated ketones remain rare. To our knowledge, only three such reactions have been reported, and all are catalyzed by chiral metal complexes.[3] Inanaga and co-workers reported a chiral scandium complex as a highly effective Lewis acid catalyst for an asymmetric aza-Michael reactions of o-alkoxyhydroxylamines to acyclic enones.[3a] Applying bifunctional catalysis with a chiral lithium-yttrium heterobimetallic complex, Shibasaki and co-workers established a highly efficient azaMichael reaction with a broader scope, affording high enantioselectivity for a wide range of a,b-unsaturated ketones 1, (see Scheme 1) bearing either an aryl or alkyl b-substituent (R 1 ). [3b,c] However, the ketone substituent (R 2 ) is limited to aromatic rings for both of the aforementioned reactions. More recently, Jacobsen and co-workers reported the conjugate addition of hydrazoic acid to enones catalyzed by a salen-aluminum complex.[3d] Notably, this reaction afforded good to excellent enantioselectivity for a,b-unsaturated ketone 1, bearing various alkyl substituents as R 1 and R 2 . Herein, we report the first highly enantioselective azaMichael reaction with a,b-unsaturated ketones catalyzed by a chiral organic catalyst. Significantly, this new catalytic asymmetric aza-Michael reaction afforded consistently excellent enantioselectivity for a wide variety of alkyl vinyl ketones bearing either an alkyl or aryl group as R 1 , thereby providing a synthetically valuable substrate scope that is complementary to those of existing chiral metal-based methods.MacMillan and co-workers [6a] first reported the use of chiral secondary amines, in this case chiral imidazolidinones, to activate a,b-unsaturated aldehydes for highly enantioselective aza-Michael reactions with N-siloxycarbamate using iminium catalysis.[8] Presumably, the steric bulk of the chiral secondary amines renders them highly chemoselective for nucleophilic attack at the aldehyde group, while minimizing catalyst decomposition through conjugate additions to enals. On the other hand, a,b-unsaturated ketones 1 are sterically more demanding and electronically less active toward iminium formation with c...

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Enantioselective catalysis 98. Preparation of 9-amino(9-deoxy)cinchona alkaloids

Cited by 127 publications

References 11 publications

Enantioselektive Katalyse photochemischer Reaktionen

Enantioselektive Katalyse photochemischer Reaktionen

Asymmetric organocatalytic Michael addition of Meldrum’s acid to nitroalkenes: probing the mechanism of bifunctional thiourea organocatalysts

Asymmetric Aza‐Michael Reactions of α,β‐Unsaturated Ketones with Bifunctional Organic Catalysts

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