C(sp³)–H Bond Acylation with N-Acyl Imides under Photoredox/ Nickel Dual Catalysis

Abstract

A novel Ni/photoredox-catalyzed acylation of aliphatic substrates, including simple alkanes and dialkyl ethers, has been developed. The method combines C–N bond activation of amides with a radical relay mechanism involving hydrogen-atom transfer. The protocol is operationally simple, employs bench-stable N-acyl imides as acyl-transfer reagents, and permits facile access to alkyl ketones under very mild conditions.

Key words

nickel catalysis - photocatalysis - acylation - radical relay - C–N bond activation - ketones

Publication History

Received: 31 July 2020

Accepted after revision: 31 August 2020

Article published online:
08 October 2020

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• 16 See the Supporting Information for more details.
• 17 Cyclohexyl(phenyl)methanone (3a); Typical Procedure A In an argon-filled glovebox, a 10 mL Schlenk tube equipped with a magnetic stirrer bar was charged with Ir{[dF(CF₃)ppy]₂(dtbbpy)}PF₆ (0.003 mmol, 3.2 mg), [Ni(dtbbpy)(H₂O)₄]Cl₂ (0.024 mmol, 11.2 mg), K₃PO₄ (1.2 mmol, 254 mg), Na₂WO₄·2 H₂O (0.6 mmol, 200 mg), LiCl (0.6 mmol, 25 mg), N-benzoylsuccinimide (0.6 mmol, 122 mg), cyclohexane (3.0 mmol, 325 μL), and anhyd benzene (6 mL). The sealed vessel was taken out of the glovebox, and the stirred mixture was irradiated by a 40 W blue LED Kessil lamp (455 nm) for 24 hours at RT. To remove solid residues, the mixture was filtered through a short pad of Celite with CH₂Cl₂ as the eluent. The volatiles were removed under vacuum and the crude residue was purified by column chromatography [silica gel, cyclohexane–EtOAc (10:1)] to give a colorless oil; yield: 60 mg (53%). The ¹H NMR and ¹³C NMR spectra were consistent with values reported in the literature.^8b
• 18 Phenyl(tetrahydrofuran-2-yl)methanone (3i); Typical Procedure B On the bench top, an 8 mL scintillation vial equipped with a magnetic stirrer bar was charged with Ir{[dF(CF₃)ppy]₂(dtbbpy)}PF₆ (0.008 mmol, 9 mg), [Ni(dtbbpy)(H₂O)₄]Cl₂ (0.04 mmol, 18.7 mg), K₃PO₄ (0.6 mmol, 127 mg), LiCl (0.4 mmol, 17 mg), N-benzoylsuccinimide (0.4 mmol, 81.3 mg), and anhyd THF (3.2 mL, 0.125 M). The vial was sparged with argon then sealed, and the stirred mixture was irradiated by a 30 W blue LED lamp (450 nm; EvoluChem PhotoRedOx Box device) for 24 h at RT. To remove solid residues, the mixture was filtered through a short pad of Celite with CH₂Cl₂ as eluent. The volatiles were removed under vacuum and the crude residue was purified by column chromatography [silica gel cyclohexane–EtOAc (10:1)] to give a colorless oil; yield: 37.5 mg (53%). The ¹H NMR and ¹³C NMR spectra were consistent with the values reported in the literature.^12b
• 19 CCDC 2018793 contains the supplementary crystallographic data for complex III. The data can be obtained free of charge from The Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/getstructures.
• 20 A single precedent has been reported for the formation of an acyl nickel(II) complex by amide C−N bond activation in which, after a ligand exchange between the transient amidate complex and a chloride ion, a Ni(II) chloride complex was isolated and structurally characterized; see: Hu J, Zhao Y, Liu J, Zhang Y, Shi Z. Angew. Chem. Int. Ed. 2016; 55: 8718
• 21 The formation of alkyl ketones deriving from a decarbonylative process with ethyl chloroformate has been recently reported; see: Shi R, Hu X. Angew. Chem. Int. Ed. 2019; 58: 7454
• 22 For the coupling of N-benzoylsuccinimide (1a) with cyclohexane, 4a could also be formed by direct attack of the cyclohexyl radical on benzene. See the Supporting Information for more details.
• 23 Mohadjer Beromi M, Brudvig GW, Hazari N, Lant HM. C, Mercado BQ. Angew. Chem. Int. Ed. 2019; 58: 6094
• 24 During the final stage of the preparation of this manuscript, a similar protocol for the acylation of C(sp3)–H bonds with N-acylsuccinimides was published, see: Lee GS, Won J, Choi S, Baik M.-H, Hong SH. Angew. Chem. Int. Ed. 2020; 59: 16933