Xavier Serra

Reactivity of pyrrole pigments. part 61: Electrochemical reduction of some s(1h)-pyrromethenones and 5-arylmethylene-3,4-dimethyl-3-pyrrolin-2-ones

Abstract The electrochemical reduction of some 5(1H)-pyrromethenones and 5-arylmethylene-3-pyrrolin-2-ones in imethylformamide (DMF) has been studied by polarography and by identification of their electrochemical reduction products. The reduction processes observed depend on the presence on the type of supporting electrolyte. LiClO4 or tetraethyl ammonium perchlorate (TEAP) and, When TEAP is used, they also depend on the presence of Water. Polarographic curves show two monoelectronic diffusion Waves in anhydrous DMF both with LiCIO4 and with TEAP. The reaction products from (Z)-3,4-dimethyl-5-[(4-methylphenyl)methylene]-3-pyrrolin-2-one and from (Z)-2-[(3,4-dimethyl-5-oxo-3-pyrrolin-2-yl)-methylene]-1H-pyrrole for the electrolysis at controlled potentials and under different experimental conditions have been isolated and identified.In all cases a stereoselective reductive dimerization occurs but, at second wave potentials, the reduction compounds corresponding to the hydrogenation of the exocyclic double bond are also formed. The electrolysis yields can be optimized in order to make the process synthetically useful.

On the electrochemical behaviour of 5(1H)-pyrromethenones and 3,4-dihydro-5(1H)-pyrromethenones@@@Notiz über das elektrochemische Verhalten von 5(1H)-Pyrromethenonen und 3,4-Dihydro-5(1H)-pyrromethenonen (Kurze Mitteilung): Short communication

Cyclic voltammetry and polarography measurements in anhydrous dimethylformamide indicate that 1,3,4,5-tetrahydro-3-methoxycarbonylmethyl-3′,4,4,4′-tetramethyl-5-oxo-2,2′-pyrromethen-5′-carboxylic acidtert-butylester [a 3,4-dihydro-5(1H)-pyrromethenone] is both easier to reduce and to oxidize than structurally related 5(1H)-pyrromethenones.ZusammenfassungCyclische Voltammetrie und Polarographie in wasserfreiem Dimethylformamid haben gezeigt, daß 1,3,4,5-Tetrahydro-3-methoxycarbonylmethyl-3′,4,4,4′-tetramethyl-5-oxo-2,2′-pyrromethen-5′-carbonsäure-tert-butylester sowohl leichter zu reduzieren als auch zu oxidieren ist als 5(1H)-Pyrromethenone mit ähnlicher Struktur.

Electrochemical reduction mechanism of 5(1H)-pyrromethenones in dimethylformamide on a mercury electrode

Abstract The mechanism of the electrochemical reduction of some 5(1H)-pyrromethenones and their aryl analogs (5-arylmethylene-3,4-dimethyl-3-pyrrolin-2-ones) in dimethylformamide on a mercury electrode, using LiClO 4 ) as supporting electrolyte, has been investigated. Polarographic and voltammetric experimental data show that 5(1H)-pyrromethenones undergo a reductive electrodimerization only through an EC mechanism, whereas their aryl analogs can also be reduced through an ECE mechanism. This different behaviour gives information about the reactivity of the bridge carbon atom of these compounds.

Reactivity of pyrrole pigments. Part VII. Autoxidation of model compounds for 5(2H)-dipyrrylmethanones and 3,4-dihydro-5(1H)-pyrromethenones

The autoxidation in alkaline media and in the dark of some 5-methyl substituted 3,4-dimethyl-3-pyrrolin-2-ones and 5-methylene substituted pyrrolidin-2-ones is studied. Both types of compounds are found to give autoxidation products that indicate very characteristic reaction pathways.