Electrochemistry Broadens the Scope of Flavin Photocatalysis: Photoelectrocatalytic Oxidation of Unactivated Alcohols

• Published in: Angewandte Chemie International Edition Vol. 59; no. 1; pp. 409 - 417
• Main Authors: Zhang, Wen, Carpenter, Keith L., Lin, Song
• Format: Journal Article
• Language: English
• Published: WEINHEIM Wiley 02.01.2020; Wiley Subscription Services, Inc
• Edition: International ed. in English
• Subjects: Alcohol; Alcohols; Alcohols - chemistry; Aliphatic alcohols; Aliphatic compounds; Benzyl alcohol; Catalysts; Chemical reactions; Chemistry; Chemistry, Multidisciplinary; Electrochemistry; Electrochemistry - methods; Flavin; Flavins - chemistry; Humans; Hydrogen peroxide; Molecular Structure; Oxidants; Oxidation; Oxidation-Reduction; Oxidizing agents; Photocatalysis; Photochemicals; Photochemistry - methods; Physical Sciences; radicals; Riboflavin; Science & Technology; Thiourea; Thioureas; CATALYTIC PHOTOOXIDATION; C-H BOND; electrochemistry; radicals; RIBOFLAVIN TETRAACETATE; ISOMERIZATION; oxidation; alcohols; ALDEHYDES; BENZYL ALCOHOLS; DISSOCIATION; ALKYL BENZENES; photocatalysis; EFFICIENT
• ISSN: 1433-7851; 1521-3773
• DOI: 10.1002/anie.201910300

Riboflavin‐derived photocatalysts have been extensively studied in the context of alcohol oxidation. However, to date, the scope of this catalytic methodology has been limited to benzyl alcohols. In this work, mechanistic understanding of flavin‐catalyzed oxidation reactions, in either the absence or presence of thiourea as a cocatalyst, was obtained. The mechanistic insights enabled development of an electrochemically driven photochemical oxidation of primary and secondary aliphatic alcohols using a pair of flavin and dialkylthiourea catalysts. Electrochemistry makes it possible to avoid using O2 and an oxidant and generating H2O2 as a byproduct, both of which oxidatively degrade thiourea under the reaction conditions. This modification unlocks a new mechanistic pathway in which the oxidation of unactivated alcohols is achieved by thiyl radical mediated hydrogen‐atom ion. Dynamic duo: The combination of electrochemistry and photochemistry allows the generation of highly reactive catalytic intermediates without the need for a chemical oxidant. This photoelectrocatalytic strategy thus accessed the elusive reactivity of flavins for oxidizing unactivated aliphatic alcohols. HAT=hydrogen‐atom transfer.