Préparation, réduction chimique et électrochimique d'α-nitrostyrylcétones — synthèse d'hétérocycles azotés

Abstract

Nitration of styryl ketones with nitrogen peroxide leads to the corresponding α-nitroethylenic ketones in good yield. However, the presence of methoxy groups involves a nitration on the aromatic nucleus.LiAlH4 reduction of α-nitrostyrylketones yields the corresponding racemic erythro- and threo-aminoalcohols; after acylation and cyclisation a dihydro-quinoline or a 2-oxazoline is obtained.Electrochemical reduction of these nitrostyryl-ketones selectively provides the α-ketoximes, which are themselves reduced electrolytically to α-aminoketones. These latter compounds dimerise in neutral medium to dihydro-2,5-pyrazines which aromatise to the corresponding pyrazines. In acid medium an α-ketol is obtained.A mechanism for the reduction is proposed implicating an enaminol intermediate.