Oxidase Catalysis via Aerobically Generated Hypervalent Iodine Intermediates

Abstract

Development of sustainable oxidation chemistry demands strategies to harness O2 as a terminal oxidant. In particular, oxidase catalysis, in which O2 serves as a chemical oxidant without necessitating oxygen incorporation into reaction products, would allow diverse substrate functionalization chemistry to be coupled to O2 reduction. Direct O2 utilization must overcome the intrinsic challenges imposed by the triplet ground state of O2 and the disparate electron inventories of four-electron O2 reduction and two-electron substrate oxidation. Here, we generate hypervalent iodine reagents, a broadly useful class of selective two-electron oxidants, from O2. Synthesis of these oxidants is achieved by intercepting reactive intermediates of aldehyde autoxidation. The use of aryl iodides as mediators of aerobic oxidation underpins an oxidase catalysis platform that couples a broad array of substrate oxidations to O2 reduction, including olefin functionalization chemistry, carbonyl α-oxidation, oxidative dearomatization, and aerobic C-H amination chemistry.

Electrochemical Oxidation Dearomatization of Anisol Derivatives toward Spiropyrrolidines and Spirolactones

“…It is worth mentioning that dearomatization spiro cyclization reaction is normally applicable to electron rich or neutral aromatic rings. The substrate with trifluoromethyl group substituted aromatic core (1f), which was generally intolerable accroding to the previous literature reports, [8][9][10][11][12][13][16][17][18][19][20][21] could be successfully transformed in this reaction. Besides, the substrates such as 4-methoxy naphthyl (1h) and 2-methoxy phenyl (1i) could also be tolerated with this method.…”

“…Inspired by their pioneering work, various methods were developed by combining catalytic amount of hypervalent iodines, halogenated compounds or noble metal species with stoichiometric amount of oxidants. [16][17][18][19][20][21] However, the substrate scope is usually limited to 1-and 2-naphthols, especially for the spiroamination and spirolactonization of arenols. Besides, Wirth and co-workers reported a novel continuous-flow electrochemical method with two steps that hypervalent iodine reagents were firstly generated from low valent aryl iodides in the reaction system and then substrates were oxidized in the next step (Scheme 1(b), Mode B).…”

Photoinduced Aerobic Iodoarene-Catalyzed Spirocyclization of N-Oxy-Amides to N-Fused Spirolactams

“…Since the oxidation potential of iodobenzene (to its radical cation) is much higher (2.17 V vs SCE) 18 than the reduction potential of oxygen (-0.33 V vs SHE, for single electron reduction at pH = 7 ), 19 .resorting to an electron-transfer mediator 20 (ETM) is mandatory. This strategy was eventually implemented in 2017, by Miyamoto & Uchiyama 21 and Powers 22 who independently reported the first examples of aerobic oxidation of iodoarenes. Their strategy relies on the transient formation of a peracid during the O2-mediated autoxidation of aldehydes into carboxylic acids.…”

“…Kita later refined this method using 2 mol% of a diiodobiaryl with 2 equivalents of peracetic acid. 38 Finally, this reaction was one of the examples that Powers 22 implemented in an aerobic fashion with 20 mol% of diiiodobenzene and 10 equivalents of acetaldehyde (Scheme 2c). For our part, we set to establish the feasibility of this transformation under aerobic conditions with an iodoarene catalyst, which would be oxidized using an organic photocatalyst (phot + ) under irradiation (Scheme 2d).…”

An Alternative One-Electron Oxidation Strategy to Access Hypervalent Iodine Reagents

“…The Powers group recently developed a powerful methodology based on O 2 -promoted aldehyde autoxidation for the conversion of iodobenzene to a variety of I(III) reagents. 8 The method could also be used for oxidative functionalizations using a catalytic amount of iodobenzene. This was important progress because the stoichiometric use of pre-formed peroxides was not needed anymore.…”