Electrochemical hydrocarboxylation of enol derivatives with CO2: access to ß-acetoxycarboxylic acids.

Electrochemical hydrocarboxylation of enol acetates with CO2 is developed. The disclosed process provides ß-acetoxycarboxylic acids in 25-66% yields, in contrast to the electrolysis of ketones, silyl enol ethers and vinyl tosylates with CO2, which leads mainly to alcohols.

Electrochemical Generation of Peroxy Radicals and Subsequent Peroxidation of 1,3-Dicarbonyls in an Undivided Cell.

The generation of peroxy radicals from hydroperoxides with subsequent selective peroxidation of 1,3-dicarbonyls in an undivided electrochemical cell under constant current conditions is reported. The method provides a variety of peroxy-containing barbituric acids and 4-hydroxy-2(5H)-furanones with yields of up to 74%. Only the combination of anodic and cathodic processes provides efficient peroxidation by generating a set of alkoxy and peroxy radicals. NaNO3 acts as both an electrolyte and a redox mediator of radical reactions.

An environmentally benign way to synthesize 2-thiocyano-1,3-dicarbonyl compounds with high antifungal activity: a key role of solvent.

The introduction of thiocyano groups into organic molecules is important for the preparation of many active ingredients and synthetic intermediates. A commonly used and attractive strategy is the nucleophilic substitution of halogens with the SCN anion or oxidative thiocyanation using an excess amount of external oxidants. A sustainable alternative to stoichiometric reagents is electrochemistry based on anodic oxidation of the SCN anion and other intermediates. Electrochemical thiocyanation of various organic compounds, carried out in the usual non-acidic organic solvents, is well known. Here, we present an electrochemical thiocyanation of 1,3-dicarbonyl compounds in which high efficiency was only achieved using AcOH as the solvent. Electrolysis proceeds in an undivided cell under constant current conditions without any additional halogen-containing electrolytes. Ammonium thiocyanate was used as the source of the SCN group and the electrolyte. Electrochemical thiocyanation of 1,3-dicarbonyl compounds begins with the generation of (SCN)2 from the thiocyanate anion, followed by the addition of thiocyanogen to the double bond of the enol tautomer of 1,3-dicarbonyl compounds, which finally gives the products. A variety of thiocyanated 1,3-dicarbonyl compounds bearing different functional groups were obtained in 37-82% yields and were shown to exhibit high antifungal activity.

Electrochemical thiocyanation of barbituric acids.

The electrochemical thiocyanation of barbituric acids with NH4SCN was disclosed in an undivided cell under constant current conditions. The electrosynthesis is the most efficient at a record high current density (janode ≈50-70 mA cm-2). NH4SCN has a dual role as the source of the SCN group and as the electrolyte. Electrochemical thiocyanation of barbituric acids starts with the generation of (SCN)2 from the thiocyanate anion. The addition of thiocyanogen to the double bond of the enol tautomer of barbituric acid gives thiocyanated barbituric acid. A variety of thiocyanated barbituric acids bearing different functional groups were obtained in 18-95% yields and were shown to exhibit promising antifungal activity.

Electrochemically Induced Intermolecular Cross-Dehydrogenative C-O Coupling of ß-Diketones and ß-Ketoesters with Carboxylic Acids.

The electrochemically induced cross-dehydrogenative C-O coupling of ß-diketones and ß-ketoesters (C-H reagents) with carboxylic acids (O-H reagents) was developed. An important feature of this reaction lies in the selective formation of intermolecular C-O coupling products in high yields, up to 92%, using DMSO as a solvent with a broad substrate scope in an undivided cell equipped with carbon and platinum electrodes at high current density. Electric current acts as a stoichiometric oxidant.

Interrupted Baeyer-Villiger Rearrangement: Building A Stereoelectronic Trap for the Criegee Intermediate.

The instability of hydroxy peroxyesters, the elusive Criegee intermediates of the Baeyer-Villiger rearrangement, can be alleviated by selective deactivation of the stereoelectronic effects that promote the 1,2-alkyl shift. Stable cyclic Criegee intermediates constrained within a five-membered ring can be prepared by mild reduction of the respective hydroperoxy peroxyesters (ß-hydroperoxy-ß-peroxylactones) which were formed in high yields in reaction of ß-ketoesters with BF3 ⋅Et2 O/H2 O2 .

A H2O2/HBr system - several directions but one choice: oxidation-bromination of secondary alcohols into mono- or dibromo ketones.

In this work we found that a H2O2-HBr(aq) system allows synthesis of α-monobromo ketones and α,α'-dibromo ketones from aliphatic and secondary benzylic alcohols with yields up to 91%. It is possible to selectively direct the process toward the formation of mono- or dibromo ketones by varying the amount of hydrogen peroxide and hydrobromic acid. The convenience of application, simple equipment, multifaceted reactivity, and compliance with green chemistry principles make the application of the H2O2-HBr(aq) system very attractive in laboratories and industry. The proposed oxidation-bromination process is selective in spite of known properties of ketones to be oxidized by the Baeyer-Villiger reaction or peroxidated with the formation of compounds with the O-O moiety in the presence of hydrogen peroxide and Bronsted acids.