Syntheses with Electrogenerated Halogens: Part II . Oxidation of Malonate Esters

Abstract

The indirect electrochemical oxidation of malonate esters (I) to ethane-1,1,2,2-tetracarboxylate esters (II) has been investigated in greater detail than previously reported. With acetonitrile or an alcohol as the solvent, ethenetetracarboxylate (III), propane-l,l,2,2,3,3-hexacarboxylate (IV), and ethane-1,1,2-tricarboxylate (V) esters were also formed. If the conversion of (I) was limited to 70%, by-product formation was low and 98% yields of (II) were obtained. In acetonitrile, current efficiency was comparable with the chemical yield, but with alcoholic solvents it was lower (70-80%) due to competing indirect oxidation of the alcohol to the corresponding alkyl formate (VI). The similar coupling of monosubstituted malonate esters (VII; giving VIII) shows a marked steric effect similar to that observed in some cyanoethylation reactions, suggesting that the coupling occurs via a nucleophilic displacement reaction. The steric effect rationalizes the absence of tetrameric and higher products. The similar cyclization of some bismalonate esters (IX; giving X) is also reported.

Photons or Electrons? A Critical Comparison of Electrochemistry and Photoredox Catalysis for Organic Synthesis

“…White demonstrated the first example of this via the electrooxidative cyclization of tetramethylpropane-1,1,3,3tetracarboxylate with sodium iodide as a mediator to form tetramethyl-cyclopropane-1,1,2,2-tetracarboxylate (108.4) in 40% yield. 1088 Cathodic reduction of the O−H proton of ethanol generates H 2 and ethoxide, enabling deprotonation of acidic protons from the substrate to form stabilized carbanion 108.11. This anion traps iodinegenerated via anodic oxidation of iodideto an alkyl iodide (108.12).…”

Recent Advances in the Electrochemical α‐C–H Bond Functionalization of Carbonyl Compounds

“…It was reported that electrochemical oxidation of tetramethyl propane‐1,1,3,3‐tetracarboxylate 45 in an undivided cell in methanol with NaI as the mediator gave tetramethyl cyclopropanetetracarboxylate 46 in 40% yield (Scheme ) . This is the first example of an electrosynthesis of cyclopropane derivatives.…”

Electrochemical synthesis of cyclopropanes

“…13 The cyclization of tetramethyl propane-1,1,3,3-tetracarboxylate (37a) carried out back in the 1970s (Ref. 38) was the first electrosynthesis of cyclopropane derivatives that employed alkali metal halides as the mediators. Tetramethyl cyclopropanetetracarboxylate (38a) was synthesized in an undivided cell in boiling methanol in the presence of NaI as the mediator in a chemical yield of 40% and a current efficiency of 82% (Scheme 24).…”