NHC-Catalyzed 1,2-Selective Hydroboration of Quinolines

Jeong, Jinseong; Heo, Joon; Kim, Dong-Wook; Chang, Sukbok

doi:10.1021/acscatal.0c00884

Cited by 24 publications

(21 citation statements)

References 52 publications

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“…Chang has subsequently shown that an N-heterocyclic carbene (NHC) will catalyze the 1,2-hydroboration of quinolines with HBpin. 76 A similar mechanism to the 1,4-hydroboration of N-heteroarenes was proposed, based on the observation of a borohydride by 11…”

Section: Scheme 6 Nucleophile-promoted Carbonyl Hydroborationmentioning

confidence: 90%

“…BH 3 accelerated the rate of reaction by activating the arene with the key step in the reaction being hydride transfer from the borohydride species to the BH 3 -activated arene. Chang has subsequently shown that an N-heterocyclic carbene (NHC) will catalyze the 1,2-hydroboration of quinolines with HBpin . A similar mechanism to the 1,4-hydroboration of N-heteroarenes was proposed on the basis of the observation of a borohydride by 11 B NMR spectroscopy from the reaction between the NHC and HBpin.…”

Section: Nucleophile-promoted Decomposition Of 132-dioxaborolanesmentioning

confidence: 99%

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The Hidden Role of Boranes and Borohydrides in Hydroboration Catalysis

et al. 2020

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The continued development of hydroboration catalysts typifies the importance of this transformation as a testbed for catalytic activity and as a fundamental reaction for organic synthesis. Catalytic hydroboration studies routinely investigated the decomposition of HBcat but in the case of HBpin, decomposition is not commonly investigated due to its perceived stability.Organoboranes catalyze the hydroboration of alkenes and alkynes; these species can be formed

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Section: Scheme 6 Nucleophile-promoted Carbonyl Hydroborationmentioning

confidence: 90%

Section: Nucleophile-promoted Decomposition Of 132-dioxaborolanesmentioning

confidence: 99%

The Hidden Role of Boranes and Borohydrides in Hydroboration Catalysis

et al. 2020

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“…In the last decade, transition-metal-catalyzed regioselective hydroboration of N -heteroarenes is reported (Scheme ). − However, hydroboration reaction on pyridine and quinoline substrates provided a mixture of 1,2- and 1,4-addition products . On the other hand, selective hydrosilylation of N -heteroaromatics also developed recently.…”

Section: Introductionmentioning

confidence: 99%

Ruthenium(II)-Catalyzed Regioselective 1,2-Hydrosilylation of N-Heteroarenes and Tetrel Bonding Mechanism

et al. 2021

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An efficient regioselective dearomatization of N-heteroarenes using a ruthenium precatalyst [Ru-(p-cymene)(PCy 3 )Cl 2 ] 1 is achieved. Reactions were performed under mild and neat conditions. A wide variety of N-heteroarenes undergo the addition of silanes in the presence of precatalyst 1, leading to exclusive N-silyl-1,2-dihydroheteroarene products. This catalytic method displays a broad substrate scope; quinolines, isoquinolines, benzimidazoles, quinoxalines, pyrazines, pyrimidines, and pyridines undergo highly selective 1,2-dearomatization. Both electron-donating and electronwithdrawing substituents on N-heteroaromatics are well tolerated in this protocol. Mechanistic studies indicate the presence of [Ru-(p-cymene) (PCy 3 )HCl] 4 in the reaction mixture, which may be the resting state of the catalyst. The complete catalytic cycle as revealed from density functional theory (DFT) studies show that the product formation is governed by N → Si tetrel bonding. Initially, PCy 3 dissociates from 1, and further reaction of [(p-cymene)RuCl 2 ] 20 with silane generates the catalytically active intermediate [(p-cymene)RuHCl] 7. Heteroarene coordinates with 7, and subsequent dearomative 1,3-hydride transfer to the C2 position of the heteroaryl ligand generates an amide-ligated intermediate in which the reaction of silane occurs through a tetrel bonding and provides a selective pathway for 1,2-addition. DFT studies also revealed that ruthenium-catalyzed 1,4-hydroboration of pyridines is a facile process with a free energy barrier of 3.2 kcal/mol, whereas a pathway for the 1,2-hydroboration product is not observed due to the steric effects exerted by methyl groups on pinacolborane (HBpin) and p-cymene. Notably, enabled by the amine−amide inter-conversion of the coordinated heteroarene ligand, the +2 oxidation state of ruthenium intermediates remains unchanged throughout the catalytic cycle.

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“…The metal-free catalytic hydroboration of N -heteroarenes was also investigated (Scheme ). When quinoline, substituted quinolines, isoquinoline, and acridine were employed, the corresponding products, 1,2-addition products and/or 1,4-addition products, 4a–f were obtained in 73–98% yields.…”

Section: Resultsmentioning

confidence: 99%