A SYNTHETIC STUDY FOR OPTICALLY ACTIVE 2H-CHROMENE TRIMERS

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Natural conocurvone is an optically active pyranonaphthoquinone trimer, and the effective synthesis of conocurvone, consist of the effective preparation of a pyranotetralone as the key compond, the respective conversions of the pyranotetralone to the corresponding hydronaphthoquinone and naphthoquinone, and followed by trimerization of both monomeric naphthoquinones, two moles of the hydroxynaphthoquinone and one mole of the naphthoquinone. In the first year, the intramolecular cyclization of 2H-chromene-6-butanoic acids, prepared by acylation of some 2H-chromene with methyl hydrogensuccinate followed by reduction and hydrolysis, was found not to be effective for the preparation of the key pyranotetralone. In the second year, the thermal cyclization of the propargyl ether of 7-hydroxy-1-tetralone was found to be most effective for the key compound. Some tetralones having a naphtho[2, 1-b] pyran structure, were preprared by the regioselective thermal cyclization of the corresponding propargyl ethers. But, a similar preparation of the chiral pyranotetralone, having the prenyl side-chain was falied, because of racemization in the the propargyl etherification, and so the thermal cyclization gave the racemic pyranotetralone. The pyranotetralone, having a prenyl side-chain, and its dimethyl analog were converted respectively to the corresponding hydroxynaphthoquinones and naphthoquinones. Thus obtained hydroxyraphthoquinone and naphthoquinone, having the prenyl side-chain, thus prepared were identical with natural teretifolione B and its deoxy derivative. Trimerization of two mole of dimethylhydroxynaphthoquinone and one mole of dimethylnaphthoquinone gave the dimethyl analog of conocurvone. The ^1H NMR showed the existence of atrop isomerism.The structural investigation for the dimethylanalogous trimer and the preparation of the chiral pyranotetralone are left to study.