Hypervalent Iodine Reagents by Anodic Oxidation: A Powerful Green Synthesis

Abstract

The anodic oxidation of aryl iodides is a powerful method for the synthesis of hypervalent iodine reagents, which eliminates the necessity to use expensive or hazardous chemical oxidizing reagents. The hypervalent iodine reagents generated at the anode are successfully used as either in-cell or ex-cell mediators for different valuable chemical transformations such as fluorinations and oxidative cyclizations. More recently, recyclable mediators and catalytic protocols have been developed.

Iodine(III)‐Mediated Electrochemical Trifluoroethoxylactonisation: Rational Reaction Optimisation and Prediction of Mediator Activity

“…In addition, these examples cover exclusively simple oxidative fluorination reactions at highly activated substrates (thioacetals, 1,3‐dicarbonyls) . More challenging reactions at unactivated substrates with more complicated reaction mechanisms or efforts towards iodine(III)‐mediated enantioselective electrochemical reactions have not been reported …”

Electrocatalytic C–N Coupling via Anodically Generated Hypervalent Iodine Intermediates

“…Subsequent oxidation chemistry would ultimately lead to I(III) (10). Alternatively, the observed acetate-dependent chemistry might arise from an interrupted Kolbe electrolysis 25 in which initially formed acetoxy radicals add to aryl iodides to generate iodanyl radical intermediates (9), which would subsequently undergo further oxidation to I(III) (10). Available evidence, summarized below, is most consistent with the former mechanistic scenario.…”

“…Hypervalent iodine reagents are a class of organic oxidants that have been deployed in a wide variety of substrate functionalization reactions. 9 Electrochemical oxidation of aryl iodides typically requires substantial overpotential, 10 thus hypervalent iodine electrochemistry has largely been limited to ex cell applications, 11 in which aryl iodides are electrolyzed in the absence of substrate and subsequently used as stoichiometric reagents, or implemented in the context of flow systems. 12,13 During the development of aerobic hypervalent iodine catalysis, 14 we discovered that the aerobic generation of hypervalent iodine compounds proceeded through the intermediacy of acetate-stabilized iodanyl radicals (i.e.…”

“…The initial interfacial electron transfer could be between the working electrode and the aryl iodide to generate an I(II) intermediate (8), which would then be trapped by exogenous acetate ion to generate acetoxy iodanyl radical 9. Subsequent oxidation chemistry would ultimately lead to I(III) (10). Alternatively, the observed acetate-dependent chemistry might arise from an interrupted Kolbe electrolysis 25 in which initially formed acetoxy radicals add to aryl iodides to generate iodanyl radical intermediates (9), which would subsequently undergo further oxidation to I(III) (10).…”

Electroorganic Synthesis under Flow Conditions

“…On the other hand, synthesis of hypervalent iodine reagents via anodic oxidation of iodoarenes eliminates the necessity of hazardous and sometimes expensive chemical oxidants and improves the ecological impact of the whole process. [37][38][39] Recently, we reported the first general approach for the synthesis of iodine(III) reagents via anodic oxidation under flow conditions. 40 Using our second-generation flow cell (Figure 2) and the Vapourtec electrochemical Ion reactor (Figure 3 Although the anodic oxidation of iodobenzene in HFIP was more efficient (100% yield) than in TFE (80% yield), the above reactions (Scheme 5) were performed using TFE rather than HFIP because the product of the electrochemical step decreased over time due to the passivation of electrodes when using HFIP which was not observed when using a glassy carbon (GC) anode and TFE (Figure 4).…”