SYNTHESIS OF PHENOLIC SESQUITERPENE ELVIROL AND ITS CONVERSION TO NAPHTHALENE DERIVATIVE

Phenolic sesquiterpene elvirol, isolated from Elvira biflora (Compositae), was synthesized through a new synthetic route and was converted to dimethylisopropylnaphthalene. 4-(2-Methoxy-5-methylbenzoyl) butyric acid [1], obtained from p-methylanisole by the Friedel-Crafts reaction with glutaric anhydride, yielded methyl 5-2-methoxy-5-methylphenyl) hexanoate [3 b] in 3 steps. 2-Methyl-6-(2-methoxy-5-methyIphenyl-2-heptene [5 b] was obtained from [3 b] by the Grignard reaction followed by dehydration. Elvirol, 2-(l, 5-dimethyl-4-hexenyl)-4-methylphenol, [5 a] was prepared by demethylation of [5 b] with boron tribromide. By heating with hydrobromic acid [5 b) was cyclized to yield 4, 5-dimethyl-8-isopropyl-5,6, 7,8-tetrahydro-l-naphthol [5 a], which gave 3,4-dihydro-4,5-dimethyl-8-isopropyl-l(2H)-naphthalenone [10 b] by heating with palladium-charcoal catalyst. Reduction of [10 b] followed by heating with sulfur afforded 1, 8-dimethyl-4-isopropylnaphthalene [8 b]. The reaction of [5 b] with other acid catalysts was also studied. In order to identify the new hydrocarbon [3 b], it was independently synthesized from p-cymene. Similarly, 1,5-dimethyl-4-isopropylnaphthalene [8 a] and 1,5,8-trimethyl-4-isopro-pylnaphthalene [3 c] were also synthesized. The hydrocarbons [3 a] and [3 b] solidified to show the melting points of 31~32°C and 32.5~33.5°C, respectively. The picrates of [3 b] and [3 c] had the wide melting point ranges. © 1979, The Chemical Society of Japan. All rights reserved.