Pd-catalyzed asymmetric hydrogenation of fluorinated aromatic pyrazol-5-ols via capture of active tautomers

Chen, Zhang‐Pei; Chen, Mu‐Wang; Shi, Lei; Yu, Chang‐Bin; Zhou, Yong‐Gui

doi:10.1039/c5sc00835b

Cited by 44 publications

(22 citation statements)

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“…Very recently, Zhou et al reported the asymmetric hydrogenation of fluorinated pyrazol‐5‐ols by capturing one of the tautomers with the aid of a strong Brønsted acid as activator. Two catalytic systems were developed for 4‐unsubstituted of 4‐substituted pyrazol‐5‐ols, based on the use of ligand L12 or L13 and TFA or L ‐CSA as activators, respectively (Scheme , g) 47. The hydrogenation of 17 examples was reported, with overall enantioselectivity in the corresponding substituted hydrogenated compounds ranging from 82 to 96 % ee .…”

Section: Strategy Iii: Hydrogenation After Breaking the Aromaticitymentioning

confidence: 99%

Substrate Activation in the Catalytic Asymmetric Hydrogenation ofN‐Heteroarenes

2015

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Different methods for transforming N-heteroarenes into more reactive derivatives for catalytic asymmetric hydrogenation are highlighted. The first strategy consists of facilitating hydrogenation by the formation of positively charged derivatives of the heteroarene. Catalyst deactivation processes arising upon binding of the substrate to the metal center can thus be prevented and, additionally, hydrogenation of positively charged heteroarenes may also be more favored than that of their neutral analogues. The second strategy is based onScheme 4. Chelation assistance during asymmetric hydrogenation of six-membered heteroarenes.(eight examples), although in some cases small quantities of partially hydrogenated compounds were detected. Enantioselectivities were generally high (up to 90 %).www.eurjoc.org

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Section: Strategy Iii: Hydrogenation After Breaking the Aromaticitymentioning

confidence: 99%

Substrate Activation in the Catalytic Asymmetric Hydrogenation ofN‐Heteroarenes

2015

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“…[14,15] Therefore, the selective transformationo fisoxazoles to isoxazolines or isoxazolidinesi saformidable task in organic chemistry. [16] The asymmetric hydrogenationo fi soxazoles is au seful method to prepare optically active isoxazolines or isoxazolidines.T hese compoundsa re often used as intermediates in the syntheses of usefulc ompounds. [17,18] The isoxazoline or isoxazolidine framework is found in some biologically active molecules.…”

Section: Introductionmentioning

confidence: 99%

Asymmetric Hydrogenation of Isoxazolium Triflates with a Chiral Iridium Catalyst

Ikeda

Kuwano

2016

Chemistry A European J

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The iridium catalyst [IrCl(cod)]2 -phosphine-I2 (cod=1,5-cyclooctadiene) selectively reduced isoxazolium triflates to isoxazolines or isoxazolidines in the presence of H2 . The iridium-catalyzed hydrogenation proceeded in high-to-good enantioselectivity when an optically active phosphine-oxazoline ligand was used. The 3-substituted 5-arylisoxazolium salts were transformed into 4-isoxazolines with up to 95:5 enantiomeric ratio (e.r.). Chiral cis-isoxazolidines were obtained in up to 89:11 e.r., with no formation of their trans isomers, when the substrates had a primary alkyl substituent at the 5-position. The mechanistic studies indicate that the hydridoiridium(III) species prefers to deliver its hydride to the C5 atom of the isoxazole ring. The hydride attack leads to the formation of the chiral isoxazolidine via a 3-isoxazoline intermediate. Meanwhile, in the selective formation of 4-isoxazolines, hydride attack at the C5 atom may be obstructed by steric hindrance from the 5-aryl substituent.

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“…Previous research have demonstrated that Brønsted acids often play as promoter to facilitate the hydrogenation through activating substrate [13] and accelerating imine-enamine [9f] or hydroxy-oxo tautomerization. [14] In addition, much progresses have been successfully achieved in palladiumcatalyzed asymmetric hydrogenation, which feature ar obust hydrogenation catalyst with high toleration to the strong Brønsted acid, oxygen and moisture. [15][16][17] Thus,i nitially,w e choose readily available 4-phenylpyrimidin-2-ol (1a)a s model substrate,P d(OCOCF 3 ) 2 /(S)-Synphos (L1)c omplex as hydrogenation catalyst and trifluoroacetic acid (TFA) as additive.The hydrogenation was run in toluene at 60 8 8Cunder 1000 psi of hydrogen.…”

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confidence: 99%

Facile Synthesis of Chiral Cyclic Ureas through Hydrogenation of 2‐Hydroxypyrimidine/Pyrimidin‐2(1H)‐one Tautomers

et al. 2018

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A facile access to optically active cyclic ureas was developed through palladium-catalyzed asymmetric hydrogenation of pyrimidines containing tautomeric hydroxy group with up to 99 % ee. Mechanistic studies indicated that reaction pathway proceed through hydrogenation of C=N of the oxo tautomer pyrimidin-2(1H)-one, acid-catalyzed isomerization of enamine-imine, and hydrogenation of imine pathway. In addition, the chiral cyclic ureas are readily converted into useful chiral 1,3-diamine and thiourea derivatives without loss of optical purity.

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Pd-catalyzed asymmetric hydrogenation of fluorinated aromatic pyrazol-5-ols via capture of active tautomers

Abstract: Here we explore a novel strategy for asymmetric hydrogenation of aromatic pyrazol-5-ols via capture of the active tautomers.

Cited by 44 publications

References 87 publications

Substrate Activation in the Catalytic Asymmetric Hydrogenation ofN‐Heteroarenes

Substrate Activation in the Catalytic Asymmetric Hydrogenation ofN‐Heteroarenes

Asymmetric Hydrogenation of Isoxazolium Triflates with a Chiral Iridium Catalyst

Facile Synthesis of Chiral Cyclic Ureas through Hydrogenation of 2‐Hydroxypyrimidine/Pyrimidin‐2(1H)‐one Tautomers

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