8-HYDROXY-SUBSTITUTED ISOCOUMARINS BY LITHIATION OF BENZENE-DERIVATIVES PROMOTED BY BETA-FUNCTIONALIZED ALKYL-GROUPS - A REGIOSELECTIVE AND SIMPLE SYNTHESIS OF OOSPOLACTONE

3-(3-hydroxyphenyl)-2-butanone (obtained in 3 steps from 3-bromophenol and 3-chloro-2-butanone) was ketalised with ethylene glycol and protected at the phenolic OH as the methoxymethyl ether. The intermediate diacetal thus obtained underwent hydrogen-metal exchange with n-butyllithium; the metallated intermediate, after carbonation, methanolysis of acetal groups and elimination of methanol, regioselectively afforded the title compound (8-hydroxy-3,4-dimethylisocoumarin).