5-Arylidene 1,3-dimethylbarbiturric acid derivatives, mild organic oxidants for allylic and benzylic alcohols.

Abstract

Various 5-arylidene 1, 3-dimethylbarbituric acid derivatives and closely related compounds were synthesized as models of redox coenzymes and used for oxidation of alcohols.Under mild neutral conditions, 5-arylidene 1, 3-dimithylbarbituric acid derivatives, especially those having an electron-withdrawing group on the aromatic ring, effectively oxidized allylic and benzylic alcohols to the corresponding carbonyl compounds. The relationship between the oxidizing ability and the structure of the oxidant (coenzyme model) was investigated and it was found that the electron density on the carbon-carbon double bond is a critical factor for the oxidation. In the case of the deuterium-labeled compound, the observed value of normal and primary isotope effect was 3.3 and so it was concluded that mechanism of this oxidation mainly involves the hydride transfer from the alcohol. An electrochemical investigation was also carried out and the redox potentials of the coenzyme models, 5-arylidene 1, 3-dimethylbarbituric acid derivatives and related compounds, were measured.