Selective Electrochemical Oxygenation of Alkylarenes to Carbonyls

Abstract

An efficient electrochemical method for benzylic C­(sp3)–H bond oxidation has been developed. A variety of methylarenes, methylheteroarenes, and benzylic (hetero)­methylenes could be converted into the desired aryl aldehydes and aryl ketones in moderate to excellent yields in an undivided cell, using O2 as the oxygen source and lutidinium perchlorate as an electrolyte. On the basis of cyclic voltammetry studies, 18O labeling experiments, and radical trapping experiments, a possible single-electron transfer mechanism has been proposed for the electrooxidation reaction.

Site-Selective Synthesis of N-Benzyl 2,4,6-Collidinium Salts by Electrooxidative C–H Functionalization

“…Lower electrolyte concentrations led to reduction in yields (entries 4, 5), along with formation of 4anisaldehyde, believed to be from addition of adventitious water or oxygen to the intermediate cation or radical, respectively. 22 The higher concentrations of electrolyte also allowed the use of higher current, reducing reaction times, and the excess collidine can be recovered in high yield and reused. 23 The scalability and robustness of the reaction is demonstrated as a 1 mmol scale reaction using recycled electrolyte under "precaution-free" conditions (no care to exclude air or moisture), gave 11 in a comparable 82% yield (entry 6).…”

“…Notably, the Coll·HBF 4 salt can be readily prepared on multigram scale and isolated as a free-flowing white powder, and the 0.6 M electrolyte solution can be prepared in batches and stored for several months on the benchtop. Lower electrolyte concentrations led to reduction in yields (entries 4, 5), along with formation of 4-anisaldehyde, believed to be from addition of adventitious water or oxygen to the intermediate cation or radical, respectively . The higher concentrations of electrolyte also allowed the use of higher current, reducing reaction times, and the excess collidine can be recovered in high yield and reused .…”

Site-Selective Synthesis of 2,4,6-Collidinium Salts via Electrooxidative C–H Functionalization

“…Lower electrolyte concentrations led to reduction in yields (entries 4, 5) along with formation of 4-anisaldehyde, believed to be from addition of adventitious water or oxygen to the intermediate cation or radical respectively. 22 The higher concentrations of electrolyte also allowed the use of higher current, reducing reaction times, and the excess collidine can be readily recovered and reused. The scalability and robustness of the reaction is demonstrated as a 1 mmol scale reaction using recycled electrolyte under "precaution-free" conditions (no care to exclude air or moisture), gave 11 in a comparable 82% yield (entry 6).…”

Controlling the Hydrophilicity of the Electrochemical Interface to Modulate the Oxygen-Atom Transfer in Electrocatalytic Epoxidation Reactions

“…[2][3][4][5] Numerous anodic and cathodic reactions have been developed, allowing the forging of useful chemical bonds, [2][3][4][5][6][7][8][9][10][11] the chemoselective functionalization of peptides and proteins 12 and even the total synthesis of natural products for which chemical synthesis has no practical solution. 13 Among these reactions, electrochemical oxygenation reactions are of particular interest as they allow for the direct and chemoselective functionalization of C-H and C=C bonds forming industrially and pharmaceutically relevant chemical functions such as enones, 14 ketones, [15][16][17][18][19][20][21][22] aldehydes, 16,19,23 lactams, 24 lactones, 25 alcohols 15,21,22,26 and epoxides. 21,22,[27][28][29][30][31][32][33][34][35][36]…”