Photoinduced Nitroarenes as Versatile Anaerobic Oxidants for Accessing Carbonyl and Imine Derivatives
Joshua K. Mitchell, Waseem A. Hussain, Ajay H. Bansode, Ryan M. O'Connor, Dan E. Wise, Michael H. Choe and Marvin Parasram*
*Department of Chemistry, New York University, New York, New York 10003, United States,
Email: parasram
nyu.edu
J. K. Mitchell, W. A. Hussain, A. H. Bansode, R. M. O'Connor, D. E. Wise, M. H. Choe, M. Parasram, Org. Lett., 2023, 25, 6517-6521.
DOI: 10.1021/acs.orglett.3c02292
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Abstract
Photoexcited nitroarenes promote anaerobic oxidations of alcohols and amines via double hydrogen atom transfer steps to provide ketones and imines. With aldehydes and imines as substrates and a different nitroarene, successive HAT and oxygen atom transfer events yield carboxylic acids and amides. The methods are amenable to a continuous-photoflow setup with reduced reaction times.
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proposed mechanism
Oxidation for benzylic/activated alcohols to ketones:
Except when otherwise stated, in an oven-dried 0.5-dram vial equipped with a stir bar was added 3,5-bis(trifluoromethyl)nitrobenzene (130 mg, 0.50 mmol, 1.0 equiv.), benzylic alcohol (0.50 mmol, 1.0 equiv.), lithium acetate (0.13 mmol, 0.25 equiv.) and 5:1 MeCN/tBuOH (2.3 mL, 0.30 M) under N2 gas. The reaction vessel was left to stir at 1000 rpm and irradiated under 390 nm Kessil lamps with a cooling fan, for 24-96 h. Completion of the reaction was determined by GCMS analysis. After the reaction was complete, the solvent was removed under a stream of nitrogen. The crude product was purified by column chromatography (0 - 5% EtOAc/Hexane) to afford the ketone products.
Oxidation for unactivated alcohols to ketones:
Except when otherwise stated, in a glove box an oven dried 1.5-dram vial equipped with a stir bar was charged 3,5-bis(trifluoromethyl)nitrobenzene (1 - 3 equiv.), alcohol (1.0 mmol, 1 equiv.), and where applicable, lithium acetate (0.40 mmol, 0.25 equiv.). Anhydrous, degassed 5:1 MeCN/tBuOH (1.0 mL, 0.36 M) was added. The reaction vessel was sealed and left to stir at 900 rpm, and the reaction was irradiated under 390 nm Kessil lamps with a cooling fan, for 24-96 h. Completion of the reaction was determined by GCMS analysis. The seal vessel was opened and K2HPO4 (2.5 mmol, 5.0 equiv.), urea (2.5 mmol, 5.0 equiv.) and formaldehyde (2.5 mmol, 5.0 equiv.) were added in the flask and left to stir for another 5-10 h or until the appearance of white solid. The contents of vial were diluted with EtOAc (20 mL) and washed with deionized H2O (100 mL) and extracted using EtOAc (3 × 30 mL). Combined organic phases were dried with NaHSO4 and concentrated in vacuo. The crude product was then purified by column chromatography (2.5 - 5% Acetone/ Hexane) to afford the ketone products.
Key Words
oxidation of alcohols, photochemistry
ID: J54-Y2023
