Borane-catalyzed metal-free hydrogenation of 2,7-disubstituted 1,8-naphthyridines

Wang, Wei; Feng, Xiujuan; Du, Haifeng

doi:10.1039/c6ob01172a

Cited by 27 publications

(9 citation statements)

References 57 publications

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“…With the diene 4j-derived chiral borane, the corresponding asymmetric hydrogenations were realized and afforded the desired products 16 in 90−96% yields with 14−74% ee's (Scheme 13). 30,31 All these reactions occurred exclusively on the alkyl-substituted rings.…”

Section: Hydrogenation Of N-heteroarenesmentioning

confidence: 99%

Frustrated Lewis Pairs Catalyzed Asymmetric Metal-Free Hydrogenations and Hydrosilylations

2017

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The use of frustrated Lewis pairs is an extremely important approach to metal-free hydrogenations. In contrast to the rapid growth of catalytic reactions, asymmetric hydrogenations are far less developed due to a severe shortage of readily available chiral frustrated Lewis pair catalysts with high catalytic activities and selectivities. Unlike the stable Lewis base component of frustrated Lewis pairs, the moisture-sensitive boron Lewis acid component is difficult to prepare. The development of convenient methods for the quick construction of chiral boron Lewis acids is therefore of great interest. In this Account, we summarize our recent studies on frustrated Lewis pair-catalyzed, asymmetric metal-free hydrogenations and hydrosilylations. To address the shortage of highly active and selective catalysts, we developed a novel strategy for the in situ preparation of chiral boron Lewis acids by the hydroboration of chiral dienes or diynes with Piers' borane without further purification, which allows chiral dienes or diynes to act like ligands. This strategy ensures the construction of a useful toolbox of catalysts for asymmetric metal-free hydrogenations and hydrosilylations is rapid and operationally simple. Another strategy is using combinations of readily available Lewis acids and bases containing hydridic and acidic hydrogen atoms, respectively, as a novel type of frustrated Lewis pairs. Such systems provide a great opportunity for using simple chiral Lewis bases as the origins of asymmetric induction. With chiral diene-derived boron Lewis acids as catalysts, a broad range of unsaturated compounds, such as imines, silyl enol ethers, 2,3-disubstituted quinoxalines, and polysubstituted quinolines, are all viable substrates for asymmetric metal-free hydrogenations and give the corresponding products in good yields with high enantioselectivities and/or stereoselectivities. These chiral catalysts are very effective for bulky substrates, and the substrate scope for these metal-free asymmetric hydrogenations has been dramatically expanded. Chiral alkenylboranes were designed to enhance the rigidity of the framework and modify the Lewis acidity through the resulting double bonds. Frustrated Lewis pairs of chiral alkenylboranes and phosphines are a class of highly effective catalysts for asymmetric Piers-type hydrosilylations of 1,2-dicarbonyl compounds, and they give the desired products in high yields and enantioselectivities. Moreover, asymmetric transfer hydrogenations of imines and quinoxalines with ammonia borane as the hydrogen source have been achieved with frustrated Lewis pair of Piers' borane and (R)-tert-butylsulfinamide as the catalyst. Mechanistic studies have suggested that the hydrogen transfer occurs via an 8-membered ring transition state, and regeneration of the reactive frustrated Lewis pair with ammonia borane occurs through a concerted 6-membered ring transition state.

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Section: Hydrogenation Of N-heteroarenesmentioning

confidence: 99%

Frustrated Lewis Pairs Catalyzed Asymmetric Metal-Free Hydrogenations and Hydrosilylations

2017

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“…It was proposed that a deprotonation of 7-methyl-1,2,3,4-tetrahydro-1,8-naphthyridine (11) with two equivalents of sec-BuLi would afford phosphonate 12 upon quenching with diethyl chlorophosphate via formation of the dianion. This could then be used in a subsequent Horner-Wadsworth-Emmons reaction to construct the carbon skeleton of amine 6.…”

Section: Resultsmentioning

confidence: 99%

“…Both reactions employ harsh conditions with limited functional group tolerance and limited regiochemical control, which presents considerable purification issues during large-scale synthesis [ 8 – 10 ]. More recently, catalytic methodologies for the asymmetric hydrogenation of 1,8-naphythyridines have been reported [ 11 – 12 ].…”

Section: Introductionmentioning

confidence: 99%

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Facile synthesis of 7-alkyl-1,2,3,4-tetrahydro-1,8-naphthyridines as arginine mimetics using a Horner–Wadsworth–Emmons-based approach

Lippa

Murphy

Barrett

2020

Beilstein J. Org. Chem.

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Integrin inhibitors based on the tripeptide sequence Arg–Gly–Asp (RGD) are potential therapeutics for the treatment of idiopathic pulmonary fibrosis (IPF). Herein, we describe an expeditious three-step synthetic sequence of Horner–Wadsworth–Emmons olefination, diimide reduction, and global deprotection to synthesise cores for these compounds in high yields (63–83% over 3 steps) with no need for chromatography. Key to this transformation is the phosphoramidate protecting group, which is stable to metalation steps.

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“…Recently, Du and coworkers described a metal‐free hydrogenation of 2,7‐disubstituted 1,8‐naphthyridines 24 using a pentafluorostyrene derived borane catalyst to produce 1,2,3,4‐tetrahydro‐1,8‐naphthyridines 25 in 83%—98% yields. With the use of chiral diene 15d instead of pentafluorostyrene, the asymmetric hydrogenation has been achieved with up to 74% ee (Scheme ) …”

Section: Chiral Boranes Synthesized Via In Situ Hydroborationmentioning

confidence: 99%

Asymmetric Catalysis with Chiral Frustrated Lewis Pairs

Meng

Feng

2020

Chin. J. Chem.

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The chemistry of frustrated Lewis pairs (FLPs) provides the most important approach for the metal-free hydrogenation and hydrosilylations. Great progress has been achieved in this area for the past decade. Some promising results have also been obtained. This perspective article mainly focuses on the recent advances for the synthesis of chiral Lewis acidic boranes in category of three protocols, 1) hydroboration of chiral internal alkenes with Piers' borane HB(C6F5)2; 2) in situ hydroboration of chiral alkenes or alkynes without any purification; 3) and substitution reaction of (C6F5)nBCl3-n with chiral organometallic reagents, as well as their applications in the metal-free asymmetric hydrogenations and hydrosilylations.

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Borane-catalyzed metal-free hydrogenation of 2,7-disubstituted 1,8-naphthyridines

Cited by 27 publications

References 57 publications

Frustrated Lewis Pairs Catalyzed Asymmetric Metal-Free Hydrogenations and Hydrosilylations

Frustrated Lewis Pairs Catalyzed Asymmetric Metal-Free Hydrogenations and Hydrosilylations

Facile synthesis of 7-alkyl-1,2,3,4-tetrahydro-1,8-naphthyridines as arginine mimetics using a Horner–Wadsworth–Emmons-based approach

Asymmetric Catalysis with Chiral Frustrated Lewis Pairs

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