Synthesis of Benzopyran-4-one and Phloroglucinol Monomethyl Ether Derivatives from the Naturally Occurring Compound (Visnagin)

The reaction of 6-formyl-7-hydroxy-5-methoxy-2-methylbenzopyran-4-one with dimethyl acetylenedicarboxylate and benzil gave the respective 4H,6H-pyrano[3,2-g]chromene and imidazolylbenzopyran derivatives. Treatment of the imidazolylbenzopyran with hydrazine hydrate or hydroxylammonium chloride yielded imidazolylpyrazolylor imidazolylisoxazolylbenzenes, while the alkaline hydrolysis of imidazolylbenzopyran afforded imidazolylacetophenone that reacted with some aromatic aldehydes to give the corresponding chalcones. Oxidation of the chalcone with hydrogen peroxide led to the formation of 6-hydroxy-4-methoxy-5-[4,5-diphenylimidazol-2-yl]-2-(4methoxybenzylidene)coumaran-3-one, while the reaction with hydrazine hydrate gave the corresponding imidazolylpyrazolinylbenzene. Also, the imidazolylacetophenone was reacted with phenylhydrazine and hydroxylammonium chloride to give the respective hydrazone and oxime products. Fischer indolization of the above hydrazone yielded the corresponding indole derivative.