The Electrochemical Reduction Of Diazodimedone: Kinetics And Thermodynamics Of The Formation Of The Carbene Anion Radical

Abstract Studies of the electrochemical reduction of 2-diazo-5,5-dimethyl-1,3-cyclohexanedione (diazodimedone or DMN 2 ) in butyronitrile and N , N -dimethylformamide indicate the DMN 2 undergoes an overall one-electron reduction in aprotic media to form the conjugate base of dimedone (DMH − ) as the principal product. In the presence of an excess of the electroinactive proton donor (EtO 2 C) 2 CH 2 , DMN 2 is reduced in an overall two-electron process to give DMH − in 78% yield. Kinetic studies in butyronitrile indicate the DMN − 2 reacts in the absence of proton donors by unimolecular loss of N 2 k = 1.0 s −1 at −84°C) to give the carbene anion radial DM − as an unobserved, short-lived intermediate. A scheme is proposed in which DM − abstracts a hydrogen to give DMH − in aprotic media and undergoes protonation to give DMH in the presence of (EtO 2 C) 2 CH 2 . DMH is subsequently reduced to DMH − by unreacted DMN − 2 . The kinetics of DMN − 2 and EtO 2 C) 2 CN − 2 reaction have been studied as a function of temperature in order to obtain thermodynamic information concerning the rate-determining step.