Chiral terpene auxiliaries IV: new monoterpene PHOX ligands and their application in the catalytic asymmetric transfer hydrogenation of ketones

Kmieciak, Anna; Krzemiński, M.

doi:10.1016/j.tetasy.2017.02.003

Cited by 6 publications

(5 citation statements)

References 38 publications

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“…More specifically, the use of transition metal-based NHC complexes as catalysts in transfer hydrogenation (TH) reactions was pioneered by Nolan’s group . Currently, TH has become the most widely applied and convenient route of transition metal-based hydrogenation reactions . The process is well established, inexpensive, and environmentally friendly as compared to alternative methods of direct hydrogenation using high pressure molecular H 2 gas …”

Section: Introductionmentioning

confidence: 99%

Transfer Hydrogenation of Ketones Catalyzed by Symmetric Imino-N-heterocyclic Carbene Co(III) Complexes

Abubakar

Bala

2020

ACS Omega

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The synthesis of new moisture-sensitive imine-functionalized N-heterocyclic carbene (NHC) precursor salts [1-(2-[(hydroxyl-benzylidene)-amino]-ethyl)-3-R-3H-imidazole-1-ium bromide; R = methyl (1a), ethyl (1b), and benzyl (1c)] is reported. Subsequent deprotonation of 1a–c and coordination of the in situ generated NHC ligands to CoBr2 led to the isolation of air-stable six-coordinate Co(III) complexes 2a–c, respectively. All the salts and complexes were fully characterized. Single-crystal X-ray analysis of 2a and 2c showed octahedral Co centers hexacoordinated to two NHC carbons, two imine nitrogen atoms, and two phenolate oxygens in the form [C^N^O(Co3+)C^N^O]. The complexes were used in the catalytic transfer hydrogenation (CTH) of a range of ketones in 2-propanol as the solvent and hydrogen donor. Based on a low catalyst concentration of 0.4 mol %, significant conversions in the range of 70–99% were recorded at high turnover frequencies up to 1635 h–1. A mechanism to account for the steps involved in the CTH of cyclohexanone by complex 2a is proposed and supported by data from cyclic voltammetry, low-resolution mass spectrometry, UV, and IR spectroscopic techniques.

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Section: Introductionmentioning

confidence: 99%

Transfer Hydrogenation of Ketones Catalyzed by Symmetric Imino-N-heterocyclic Carbene Co(III) Complexes

Abubakar

Bala

2020

ACS Omega

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“…In 2017, we published the synthesis and application of pinene derived PHOX ligands in ruthenium catalyzed asymmetric transfer hydrogenation of ketones (Table 1) [36]. We reduced ketones using 0.05 mol % of the catalyst with ligand 8.…”

Section: Introductionmentioning

confidence: 99%

“…When we applied ligand 9, we obtained alcohols with lower yields and enantiomeric excesses. Most likely this is due to the trans position of the oxazoline ring in ligand 9 relative to the gem-dimethyl bridge in the pinane system [36].…”

Section: Introductionmentioning

confidence: 99%

Synthesis of 2-Amino-apopinan-3-ol and Applications of Its Derivatives in Asymmetric Reduction of Ketones

Kmieciak

Krzemiński

2019

The 23rd International Electronic Conference on Synthetic Organic Chemistry

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Monoterpenes are optically active compounds which occur in nature. This fact makes them interesting precursors for the synthesis of optically active ligands, which can be applied in various asymmetric reactions. In this work, we present the synthesis of optically pure 2-aminoapopinan-3-ol from (−)-α-pinene. The obtained amino alcohol was used as a precursor of oxazaborolidine, which was used as catalyst in the asymmetric reduction of aryl-alkyl ketones with borane. In the second part, we transformed 2-amino-apopinan-3-ol into PHOX ligand in a threestep reaction. The complex of ruthenium precursor with PHOX ligand was used as a catalyst in the asymmetric transfer hydrogenation of aryl-alkyl ketones. Alcohols with enantiomeric excesses of up to 97% were isolated using both reduction methods.

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“…Recently, we have shown the synthesis and applications of chiral PHOX ligands that were obtained from readily available natural (1 S )-β-pinene and (1 S )-α-pinene [18]. We applied these ligands for the formation of the ruthenium complexes, which were successfully used as catalysts in asymmetric transfer hydrogenation of prochiral ketones.…”

Section: Introductionmentioning

confidence: 99%

Chiral terpene auxiliaries V: Synthesis of new chiral γ-hydroxyphosphine oxides derived from α-pinene

Kmieciak¹,

Krzemiński²

2019

Beilstein J. Org. Chem.

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New chiral regioisomeric γ-hydroxyphosphine ligands were synthesized from α-pinene. The key transformation was the thermal [2,3]-sigmatropic rearrangement of allyldiphenylphosphinites, obtained from (1R,2R,4S,5R)-3-methyleneneoisoverbanol and (1R,2R,3R,5R)-4-methyleneneoisopinocampheol, to allylphosphine oxides. Hydroxy groups were introduced stereoselectively through a hydroboration–oxidation reaction proceeding from the less hindered site providing a trans relationship between the hydroxy and the phosphine substituents.

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Chiral terpene auxiliaries IV: new monoterpene PHOX ligands and their application in the catalytic asymmetric transfer hydrogenation of ketones

Cited by 6 publications

References 38 publications

Transfer Hydrogenation of Ketones Catalyzed by Symmetric Imino-N-heterocyclic Carbene Co(III) Complexes

Transfer Hydrogenation of Ketones Catalyzed by Symmetric Imino-N-heterocyclic Carbene Co(III) Complexes

Synthesis of 2-Amino-apopinan-3-ol and Applications of Its Derivatives in Asymmetric Reduction of Ketones

Chiral terpene auxiliaries V: Synthesis of new chiral γ-hydroxyphosphine oxides derived from α-pinene

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