Hydroboration

Zaidlewicz, M.

doi:10.1002/0471238961.0825041826010904.a01

Cited by 5 publications

(4 citation statements)

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“…Because organoboron compounds are versatile synthetic intermediates for constructing carbon–carbon and carbon–heteroatom bonds, hydroboration has been investigated extensively since its discovery . Many boron reagents have been designed to modulate the chemo-, regio-, and stereoselectivity of the reaction, including those that create stereogenic centers at which the carbon–boron bond is formed. , …”

Section: Introductionmentioning

confidence: 99%

Mechanistic Studies of Copper-Catalyzed Asymmetric Hydroboration of Alkenes

Hartwig

2017

J. Am. Chem. Soc.

141

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Mechanistic studies of the copper-catalyzed asymmetric hydroboration of vinylarenes and internal alkenes are reported. Catalytic systems with both DTBM-SEGPHOS and SEGPHOS as the ligands have been investigated. With DTBM-SEGPHOS as the ligand, the resting state of the catalyst, which is also a catalytic intermediate, for hydroboration of 4-fluorostyrene is a phenethylcopper(I) complex ligated by the bisphosphine. This complex was fully characterized by NMR spectroscopy and X-ray crystallography. The turnover-limiting step in the catalytic cycle for the reaction of vinylarenes is the borylation of this phenethylcopper complex with pinacolborane (HBpin) to form the boronate ester product and a copper hydride. Experiments showed that the borylation occurs with retention of configuration at the benzylic position. β-Hydrogen elimination and insertion of the alkene to reform this phenethylcopper complex is reversible in the absence of HBpin but is irreversible during the catalytic process because reaction with HBpin is faster than β-hydrogen elimination of the phenethylcopper complex. Studies on the hydroboration of a representative internal alkene, trans-3-hexenyl 2,4,6-trichlorobenzoate, which undergoes enantio- and regioselective addition of HBpin catalyzed by DTBM-SEGPHOS, KOtBu, and CuCl, also was conducted, and these studies revealed that a DTBM-SEGPHOS-ligated copper(I) dihydridoborate complex is the resting state of the catalyst in this case. The turnover-limiting step in the catalytic cycle for hydroboration of the internal alkene is insertion of the alkene into a copper(I) hydride formed by reversible dissociation of HBpin from the copper dihydridoborate species. With SEGPHOS as the ligand, a dimeric copper hydride was observed as the dominant species during the hydroboration of 4-fluorostyrene, and this complex is not catalytically competent. DFT calculations provide a view into the origins of regio- and enantioselectivity of the catalytic process and indicate that the charge on the copper-bound carbon and delocalization of charge onto the aryl ring control the rate of the alkene insertion and the regioselectivity of the catalytic reactions of vinylarenes.

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Section: Introductionmentioning

confidence: 99%

Mechanistic Studies of Copper-Catalyzed Asymmetric Hydroboration of Alkenes

Hartwig

2017

J. Am. Chem. Soc.

141

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“…Catalytic hydroelementations are fundamental transformations with high scientific and commercial relevance that pioneer numerous carbon–carbon and carbon–heteroatom bond forming reactions and are thus extensively employed in the production of cermet, natural products, agrochemicals, polyesters, dyes, pharmaceuticals, etc . Among various hydroelementation reactions, hydroboration, the addition of a B–H moiety across various unsaturated functionalities such as nitriles, alkenes, alkynes, carbonyls, etc., has drawn the growing interest of researchers worldwide. , Amidst the common unsaturated moieties, the CN bond in organonitrile compounds is exceptionally robust because of the high bond dissociation energy (750.0 kJ/mol), which makes its functionalization very challenging . Traditionally, nitrile is reduced utilizing pyrophoric reagents such as LiAlH 4 or NaBH 4 , but these protocols remained less attractive due to poor yields, product selectivity, and generation of large quantities of inorganic waste .…”

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confidence: 99%

Silver-Catalyzed Hydroboration of C–X (X = C, O, N) Multiple Bonds

2021

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AgSbF6 was developed as an effective catalyst for the hydroboration of various unsaturated functionalities (nitriles, alkenes, and aldehydes). This atom-economic chemoselective protocol works effectively under low catalyst loading, base- and solvent-free moderate conditions. Importantly, this process shows excellent functional group tolerance and compatibility with structurally and electronically diverse substrates (>50 examples). Mechanistic investigations revealed that the reaction proceeds via a radical pathway. Further, the obtained N,N-diborylamines were showcased to be useful precursors for amide synthesis.

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“…A number of reviews have been published on catalytic hydroborations, however they are now dated, or only cover a subset of catalytic hydroborations. 41–62 This field of chemistry has had a resurgence in recent years and we hope to represent some of the major advances in this area.…”

Section: Introductionmentioning

confidence: 99%