Chemo‐ and Enantioselective Brønsted Acid‐Catalyzed Reduction of α‐Imino Esters with Catecholborane

Enders, Dieter; Rembiak, Andreas; Stöckel, Bianca A.

doi:10.1002/adsc.201300352

Cited by 34 publications

(8 citation statements)

References 96 publications

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“…α-Imino acid derivatives are highly popular and versatile compounds that are employed as starting materials in a variety of transformations . In particular, α-keto imine esters and amides are largely used in asymmetric synthesis of natural and non-natural α-amino acids, Friedel–Crafts and Mannich-type reactions, organometallic and Michael additions, and cycloaddition/cyclization reactions . Most commonly, they are prepared from α-keto acid derivatives followed by imination (Scheme a) .…”

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confidence: 99%

Direct α-Imination of N-Acyl Pyrazoles with Nitrosoarenes

et al. 2019

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Unprecedented α-imino N-acyl pyrazoles were efficiently and selectively prepared through the 1,5,7-triazabicyclo[4.4.0]dec-5-ene (TBD)-catalyzed reaction of nitrosoarenes with N-acyl pyrazoles via an N-nitroso aldol reaction/dehydration sequence. The α-imino acyl pyrazoles were demonstrated to be new versatile intermediates for practical one-pot syntheses of α-imino amides, dipeptide precursors, esters, and β-amino alcohols. The synthetic method competes with known protocols in terms of ready availability of the reagents and catalyst, mild and catalytic reaction conditions, gram-scale applicability, and scope of the α-imino acid derivatives achievable.

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confidence: 99%

Direct α-Imination of N-Acyl Pyrazoles with Nitrosoarenes

et al. 2019

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“…[13] A report by Enders and co-workers describes the use of achiral Brønsted acid for imine reduction employing catecholborane as the terminal reductant (Scheme 1), with aryl a-imino ester substrates giving optimal enantioinduction. [14] Hydridic diazaphospholenes are an emerging class of reductive catalysts.F ollowing the original demonstration from Gudat and co-workers of diazaphospholene hydridicity in stoichiometric transformations, [15] Kinjo and co-workers demonstrated catalytic carbonyl and diazene reductions. [16] Our group recently demonstrated the application of neopentoxy diazaphospholene precatalysts for imine reduction with low catalyst loadings at ambient temperatures (2 mol %).…”

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Asymmetric Imine Hydroboration Catalyzed by Chiral Diazaphospholenes

et al. 2017

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The first use of diazaphospholenes as chiral catalysts has been demonstrated with enantioselective imine hydroboration. A chiral diazaphospholene prepared in a simple three-step synthesis from commercial materials has been shown to achieve the highest enantioselectivity for the hydroboration of alkyl imines with pinacolborane reported to date. Enantiomer ratios of up to 88:12 were obtained with low (2 mol %) catalyst loadings. Twenty examples of asymmetric reduction employing this main-group catalysis protocol, including the synthesis of the pharmaceuticals ent-rasagiline and fendiline, are shown.

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“…Enders has recently described the reduction of ketoimines and α-imino esters with catecholborane via Brønsted acid catalysis. 30 Under optimized conditions, various electron-rich as well as electron-deficient aromatic α-imino esters with different substitution patterns were reduced in very good enantioselectivity and high chemical yield.…”

Section: Catalysis Science and Technology Perspectivementioning

confidence: 99%

Organocatalytic strategies for enantioselective metal-free reductions

Rossi

Benaglia

Massolo

et al. 2014

Catal. Sci. Technol.

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One of the most important chemical transformations is the reduction of multiple bonds, carbon-carbon as well as carbon-heteroatom double bonds, since it leads very often to the generation of new stereocenters in the molecule. The replacement of metal-based catalysts with equally efficient metal-free counterparts is very appealing in view of possible future applications of non toxic, low cost, and environmentally friendly promoters on an industrial scale. This perspective will focus specially, but not exclusively, on the enantioselective reduction of the carbon nitrogen double bond; despite the historical need for and continued interest in chiral amines, their synthesis remains challenging. Three metal-free catalytic methodologies available for the reduction of carbon-nitrogen double bond will be discussed: i) binaphthol-derived phosphoric acids catalyzed reductions, with dihydropyridine-based compound as the reducing agent; ii) trichlorosilane mediated reductions, in the presence of catalytic amounts of chiral Lewis bases; iii) metal-free hydrogenation of imines through FLP (Frustrated Lewis Pair) methodology, that involves the use of a combination of a strong Lewis acid with a variety of sterically encumbered Lewis bases, for examples phosphines or tertiary amines, to activate hydrogen at ambient conditions. Special attention will be devoted to the most recent applications of the last five years.

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Chemo‐ and Enantioselective Brønsted Acid‐Catalyzed Reduction of α‐Imino Esters with Catecholborane

Cited by 34 publications

References 96 publications

Direct α-Imination of N-Acyl Pyrazoles with Nitrosoarenes

Direct α-Imination of N-Acyl Pyrazoles with Nitrosoarenes

Asymmetric Imine Hydroboration Catalyzed by Chiral Diazaphospholenes

Organocatalytic strategies for enantioselective metal-free reductions

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