Further Studies on Ni/Zr-mediated One-pot Ketone Synthesis: Use of a Mixture of NiI- and NiII-catalysts Greatly Improves the Molar Ratio of Coupling Partners

Umehara, Atsushi; Kishi, Yoshito

doi:10.1246/cl.190405

Cited by 12 publications

(23 citation statements)

References 24 publications

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“…To this end, we set out to investigate a catalytic protocol for the ring opening of epoxides using zirconocene with photocatalysts, although zirconocene(III) has been scarcely utilized in organic synthesis. [46][47][48][49][50][51][52][53][54][55][56][57] Since the reduction of zirconocene typically requires a high reducing power (E 1/2 (Cp 2 ZrCl 2 ) = À1.85 V versus SCE), 58 we commenced with strongly reducing photocatalyst Ir(4-MeOppy) 3 (P1, E 1/2 Ir(IV)/Ir(III)* = À1.95 V versus SCE in MeCN). 59 Visible-light irradiation of 1A in the presence of zirconocene dichloride, P1, and 1,4-cyclohexadiene (CHD) in PhCF 3 furnished a promising amount of the more substituted alcohol 2A.…”

Section: Reductive Ring Opening Of Epoxidesmentioning

confidence: 99%

Catalytic reductive ring opening of epoxides enabled by zirconocene and photoredox catalysis

Aida

Hirao

Funabashi

et al. 2022

Chem

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Section: Reductive Ring Opening Of Epoxidesmentioning

confidence: 99%

Catalytic reductive ring opening of epoxides enabled by zirconocene and photoredox catalysis

Aida

Hirao

Funabashi

et al. 2022

Chem

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“…An open question with two-ligand nickel systems is the origin of the synergistic effect, as exemplified in Scheme C: how do two poor catalysts combine to result in high yields of the cross-product? Based upon our own studies and literature data, , we propose two connected catalytic cycles for product formation (Scheme ). The first cycle is catalyzed by ( L1 )Ni and is poorly selective for the product over bialkyl when the aryl bromide is deactivated for oxidative addition compared to the alkyl bromide.…”

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confidence: 99%

Zinc-free, Scalable Reductive Cross-Electrophile Coupling Driven by Electrochemistry in an Undivided Cell

et al. 2022

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Nickel-catalyzed reductive cross-electrophile coupling reactions are becoming increasingly important in organic synthesis, but application at scale is limited by three interconnected challenges: a reliance on amide solvents (complicated workup, regulated), the generation of stoichiometric Zn salts (complicated isolation, waste disposal issue), and mixing/activation challenges of zinc powder. We show here an electrochemical approach that addresses these three issues: the reaction works in acetonitrile with diisopropylethylamine as the terminal reductant in a simple undivided cell [graphite(+)/nickel foam(−)]. The reaction utilizes a combination of two ligands, 4,4′-di-tert-butyl-2,2′-bipyridine and 4,4′,4″-tri-tert-butyl-2,2′:6′,2″-terpyridine. Studies show that, alone, the bipyridine nickel catalyst predominantly forms the protodehalogenated aryl and aryl dimer, whereas the terpyridine nickel catalyst predominantly forms the bialkyl and product. By combining these two unselective catalysts, a tunable, general system results because excess radicals formed by the terpyridine catalyst can be converted to the product by the bipyridine catalyst. As the aryl bromide becomes more electron-rich, the optimal ratio shifts to have more of the bipyridine nickel catalyst. Finally, examination of a variety of flow-cell configurations establishes that batch recirculation can achieve higher productivity (mmol product/time/electrode area) than single-pass flow, that high flow rates are essential for maximizing current, and that two flow cells in parallel can nearly halve the reaction time. The resulting reaction is demonstrated on gram scale and should be scalable to kilogram scale.

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“…The completion of the synthesis is outlined in Scheme . Recently developed Ni(I)/Ni(II)-mediated one-pot ketone synthesis was adopted to couple the right half ( 30 ) with the left half ( 6 ) with a 1.0:1.2 molar ratio of coupling partners, to afford ketone 31 in 76% yield …”

Section: Resultsmentioning

confidence: 99%

Total Synthesis of Halistatins 1 and 2

Kumar

Kishi

2020

J. Am. Chem. Soc.

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The first total synthesis of halistatins 1 and 2 has been completed using Cr-mediated coupling reactions for the C11/C12, C17/C18, and C19/C20 bond formation. For the C11/C12 bond formation, a stoichiometric Ni/Cr-mediated reaction is used to couple an α-quaternary aldehyde with a vinyl iodide. The solubilized Cr-reagent, prepared from CrCl2 and a sulfonamide ligand, allows one to perform the coupling with ∼1 equiv of Cr-reagent. Catalytic, asymmetric Co/Cr-mediated iodoallylation is adopted to incorporate the requisite C17–C19 functionality in a stereoselective manner. Asymmetric Ni/Cr-mediated coupling is used to form the C19/C20 bond effectively. Through this study, it has been found that the stereoselectivity of [5,5]-spiroketalization dramatically depends on solvents; p-toluenesulfonic acid (PTSA) in 1:1 methanol–water gave a >20:1 stereoselectivity favoring the natural series. This condition is also effective to isomerize C38-epi-halichondrins into C38 natural halichondrins.

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Further Studies on Ni/Zr-mediated One-pot Ketone Synthesis: Use of a Mixture of NiI- and NiII-catalysts Greatly Improves the Molar Ratio of Coupling Partners

Cited by 12 publications

References 24 publications

Catalytic reductive ring opening of epoxides enabled by zirconocene and photoredox catalysis

Catalytic reductive ring opening of epoxides enabled by zirconocene and photoredox catalysis

Zinc-free, Scalable Reductive Cross-Electrophile Coupling Driven by Electrochemistry in an Undivided Cell

Total Synthesis of Halistatins 1 and 2

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