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Synlett
DOI: 10.1055/a-2495-3429
DOI: 10.1055/a-2495-3429
letter
Visible-Light-Mediated Benzylic Oxidation Using Bromo(diphenyl) methane
We are grateful for financial support from the Research Grants Council of the Hong Kong Special Administration Region (Projects CUHK 14305621 and 14302221), The Chinese University of Hong Kong direct grants (Project 4053565, 4053505), Croucher Foundation Senior Research Fellowship (SRF22403), and the Innovation and Technology Commission to the State Key Laboratory of Synthetic Chemistry (GHP/004/16GD).
Abstract
Benzylic C(sp3)–H oxidation is a useful process that can give aryl carbonyl compounds as valuable building blocks. Here, we report a study on the use of bromo(diphenyl)methane as a Br source for a phototriggered benzylic oxidation. The reaction conditions are mild and compatible with a variety of substrates. Mechanistic studies suggest that the reaction might involve a peroxyl radical intermediate formed by a reaction between a benzylic C radical and molecular oxygen.
Key words
bromine - chemoselectivity - free radicals - ketones - photooxidation - bromodiphenylmethaneSupporting Information
- Supporting information for this article is available online at https://doi.org/10.1055/a-2495-3429.
- Supporting Information
Publikationsverlauf
Eingereicht: 02. Oktober 2024
Angenommen nach Revision: 03. Dezember 2024
Accepted Manuscript online:
03. Dezember 2024
Artikel online veröffentlicht:
16. Dezember 2024
© 2024. Thieme. All rights reserved
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- 13 Benzylic Oxidations with Bromo(diphenyl)methane; General Procedure Bromo(diphenyl)methane (0.08 mmol, 0.8 equiv) was added to a solution of the appropriate benzylic substrate 1 (0.1 mmol, 1 equiv) in anhyd MeOH (1 mL) in a round-bottomed flask equipped with an oxygen balloon. The mixture was irradiated by a 30 W blue LED at 35 °C until the starting material was consumed, then concentrated under reduced pressure. The residue was purified by flash column chromatography [silica gel, hexane–EtOAc (9:1)]. Methyl Benzoate (2a) Colorless oil; yield: 92%. 1H NMR (500 MHz, CDCl3): δ = 8.05–8.03 (m, 2 H, ArH), 7.57–7.54 (m, 1 H, ArH), 7.45–7.42 (m, 2 H, ArH), 3.92 (s, 3 H, CH3). 13C NMR (500 MHz, CDCl3): δ = 167.2, 132.9, 130.2, 129.6, 128.5, 128.4, 52.1. HRMS (APCI): m/z [M + H]+ calcd for C8H9O2: 137.0597; found: 137.0600. Xanthone (2j) White solid; yield: 91%. 1H NMR (400 MHz, CDCl3): δ = 8.38–8.32 (dd, J = 8.0 Hz, 2 H, Ar H), 7.76–7.70 (m, 2 H, Ar H), 7.53–7.48 (m, 2 H, Ar H), 7.41–7.36 (m, 2 H, Ar H). 13C NMR (500 MHz, CDCl3): δ = 177.4, 156.4, 135.0, 126.9, 124.1, 118.1. HRMS (APCI): m/z [M + H]+ calcd for C13H9O2: 197.0597; found: 197.0599.
For selected examples, see:
For selected examples, see: