On the reactivity of anodically generated trifluoromethyl radicals toward aryl alkynes in organic/aqueous media

• Published in: Organic & biomolecular chemistry Vol. 17; no. 14; pp. 3529 - 3537
• Main Authors: Jud, Wolfgang, Kappe, C. Oliver, Cantillo, David
• Format: Journal Article
• Language: English
• Published: CAMBRIDGE Royal Soc Chemistry 03.04.2019; Royal Society of Chemistry
• Subjects: Alkynes; Anodizing; Aqueous solutions; Aromatic compounds; Cartesian coordinates; Chemistry; Chemistry, Organic; Electrode materials; Ketones; Mathematical analysis; NMR; Nuclear magnetic resonance; Organic chemistry; Oxidation; Physical Sciences; Radicals; Science & Technology; Selectivity; Sodium; Substitution reactions; Substrates; KETONES; FLUORINE; ALPHA-TRIFLUOROMETHYLATION; OXIDATIVE TRIFLUOROMETHYLATION; DERIVATIVES; SILYL ENOL ETHERS
• ISSN: 1477-0520; 1477-0539; 1477-0539
• DOI: 10.1039/c9ob00456d

An in-depth study of the reaction of electrochemically generated trifluoromethyl radicals with aryl alkynes in the presence of water is presented. The radicals are readily generated by anodic oxidation of sodium triflinate, an inexpensive and readily available CF 3 source, with concomitant reduction of water. Two competitive pathways, i.e. aryl trifluoromethylation vs . oxytrifluoromethylation of the alkyne, which ultimately lead to the generation of α-trifluoromethyl ketones, have been observed. The influence of several reaction parameters on the reaction selectivity, including solvent effects, electrode materials and substitution patterns on the aromatic ring of the substrate, has been investigated. A mechanistic rationale for the generation α-trifluoromethyl ketones based on cyclic voltammetry data and radical trapping experiments is also presented. DFT calculations carried out at the M06-2X/6-311+G(d,p) level on the two competing pathways account for the observed selectivity. Two competing pathways have been experimentally observed and the selectivity has been explained by means of DFT calculations.