الفهرس 
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Abstract
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 addition of nitrogen atom of the solvent acetonitrile to the formed 7-oxocoumarin carbocation and regioselective cyclization to give the oxazolo[4,5-g]coumarin derivatives.
The 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 at the measured oxidation voltage (vs. Ag/10-2 N Ag+) in presence of inert gas as nitrogen.
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 to form the hydroxy benzoxazole which in turn cyclized with ethylacetoacetate in conc. H2SO4 to form the product 4.
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 intermediate which is thermodynamically unstabilized by its conjugation with the carbonyl group of the pyranoic ring.
Author 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 acetonitrile to the formed O-quinone derivative and formation of the product 9.
Finally 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 and using different spectroscopic methods as IR, 1HNMR and mass spectrum.