Photoinduced Hydrocarboxylation via Thiol-Catalyzed Delivery of Formate Across Activated Alkenes
Sara N. Alektiar and Zachary K. Wickens*
*Department of Chemistry, University of Wisconsin-Madison, Madison, Wisconsin 53706, United States, Email: wickenswisc.edu
S. N. Alektiar, Z. K. Wickens, J. Am. Chem. Soc., 2021, 143, 13022-13028.
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A photochemical process for the preparation of carboxylic acids from formate salts and alkenes proceeds in high yields across diverse functionalized alkene substrates with excellent regioselectivity. This operationally simple and redox-neutral hydrocarboxylation can be readily scaled in batch at low photocatalyst loading (0.01% photocatalyst).
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Proposed Thiol-Catalyzed Radical Chain Mechanism
General Procedure A ľ Standard Conditions
Potassium formate (92.5 mg, 1.1 equiv, 1.10 mmol) and 4DPAIPN (0.8 mg, 0.001 equiv, 1.00 Ámol) were added to a 20 mL scintillation vial (oven-dried, cooled in desiccator). Alkene* (1 equiv, 1.00 mmol), methyl thiosalicylate (2.8 ÁL, 0.02 equiv, 20.00 Ámol), and 15 mL of DMSO were added to the vial and capped with a teflon cap. With fan cooling, irradiate with a 467 nm Kessil lamp for 2 h.
*If alkene has an inhibitor present, filter off the inhibitor by passing through ~1 in basic alumina immediately prior to use.
For product isolation: Reaction mixture was transferred to a 500 mL sep funnel with 2x2 mL EtOAc, 2x2 mL 10% HCl 20% brine aq solution, 2x2 mL EtOAc. 250 mL 10% HCl 20% brine aq solution was added and the mixture was extracted 3x100 mL EtOAc. Combined organic layers were washed with brine, dried over Na2SO4 and MgSO4, and concentrated. The product was then purified via column chromatography (gradient of EtOAc and 1% AcOH in hexanes). To remove residual AcOH after purification, the product was azeotroped with benzene.