濃オルト燐酸によるカルコンのフラバノン閉環 (第4報)

フロログルシンベンジルエーテル系カルコン類の閉環

抄録

By benzylation of 3-methylphloroacetophenone (I), its O⁴, O⁶-dibenzyl ether (II) and O⁶-monobenzyl ether (III) were obtained. The chalcones obtained from the catalytic reduction product of the methylated compound (IV) of (II), 2-methoxy-3-methyl-4, 6-dihydroxyacetophenone, and its O⁴-methyl ether, underwent cyclization to the corresponding flavanones in 40% yield by heating for 5 minutes with glacial acetic acid and conc. phoshoric acid. The cyclization of the chalcones (XII, XIV, XXI, and XXIII) possessing benzyl group, derived from 2-methoxy-3-methyl-4-benzyloxy-6-hydroxyacetophenone, obtained by hydrolysis of (IV) with hydrochloric acid, (II), (III), and O⁴-methyl ether of (III), required longer time. Although (XII) afforded the corresponding flavanone, (XIV), possessing 6-benzyloxy group, (XXI), and (XXIII) afforded flavanones with the benzyl group next to the carbonyl liberated, 4′-methoxy-5-hydroxy-7-benzyloxy-8-methyl-, 4′-methoxy-5, 7-dihydroxy-8-methyl-, and 4′, 7-dimethoxy-5-hydroxy-6-methylflavanones (XXVI) in a low yield. (XXVI) was also formed by the methylation of 4′-methoxy-5, 7-dihydroxy-6-methyl-flavanone, the Friedel-Crafts reaction product of 2-methylphloroglucinol and 4-methoxycinnamoyl chloride.