ANODIC OXIDATION OF SOME HYDROXY COUMARIN DERIVATIVES

The synthetic strategy deals with the behaviour of 7-hydroxy coumarin derivatives towards anodic oxidation. The mechanism of the reaction involves the formation of 7-oxocoumarin carbocation by the loss of two electrons and one proton followed by the additThe synthesis of the following 7-hydroxycoumarin derivatives (3a-f) was carried out as literature describes and the anodic oxidation of each one was performed in pure acetonitrile and lithium perchlorate as supporting electrolyte, using two Pt-electrodes The compound 7-hydroxy-4-methylcoumarin in 3a was electrochemically oxidised to give the adduct 2,8-dimethyl-oxazolo[4,5-g]coumarin derivative 4 in 32.7% yield, the product 4 was proved authentically by the reaction of 4-aminoresorcinol with P2O5/CH3COOH Also the anodic oxidation of compound 3b afford the oxazolocoumarin 5 in 43.1% yield. In this reaction the phenyl group in 4-position increase the stability of the intermediate cation.In case of compound 3c, the product of the anodic oxidation was 2,8-dimethyl-7-propyloxazolo[4,5-g]coumarin derivative 6 in 33.8% yield. The Author thought that the loss yield of product 4, 6 may be attributed to the law stability of the carbnium ion inteAuthor noteworthy result was the electrochemical oxidation of compound 3d and between different products we can identify the product 7 as a major product.Furthermore, the anodic oxidation of 7,8-dihydroxy-4-phenylcoumarin 3e results in the formation of 4-hydroxy-2-methyl-8-phenyloxazolo[4,5-g]coumarin derivative 9 in 39% yield, the mechanism of the reaction involves two possible ways for the addition of acFinally the anodic oxidation of 4-carbomethoxy-7-hydroxycoumarin 3f afforded the adduct oxazolo[4,5-g]coumarin derivative 11 in 38.2% yield. The structure of the isolated oxazolocoumarin derivatives was confirmed on the basis of correct analytical data an