Higher terpene derivatives. III. The naphthalene hydrocarbons cadalene and eudalene, two aromatic sources of the sesquiterpenes

Abstract

Since the hydrocarbons C15H24 and the tertiary alcs. C15H26O are the chief representatives of the natural sesquiterpenes they can be classified somewhat satisfactorily upon the basis of the mol. refractivity into 4 groups; viz., (1) tricyclic, d. 0.935-0.91, MD 64.4; (2) dicyclic, d. 0.92-0.90, MD 66.1; (3) monocyclic, d. 0.873, MD; 67.8; and (4) aliphatic, d. 0.84, MD 69.5. Semmler (Ber. 46, 1817; 47, 2557) has further subdivided on the basis of density the tricyclic sesquiterpenes into (a) the cedrene family, d. 0.935, and the (b) ╬▒-santalene family, d. 0.91, and the dicyclic sesquiterpenes into (a) the cadinene family, d. 0.917, and (b) the caryophyllene family, d. 0.90. Farnesol, an aliphatic alc., is the only member of the whole sesquiterpene series whose exact constitution is known (Ber. 46, 1732). Wallach has suggested (Ann. 239, 49) a hydrogenated C10H8 ring for the structure of the polycyclic sesquiterpenes. Semmler wishes to limit this structure to the sub-groups (a). R., M. and M. have furnished the first exptl. support to this view by the dehydrogenation of cadinene by S to a C10H8 hydrocarbon, C15H18 (cf. C. A. 15, 3476). They have applied the same treatment to calamene, isozingiberene, and their new alc. from Java citronella, and in each case obtained the same C15H18, d. 0.979, b. 291┬░ MD 67.78┬░, for which they have proposed the name cadalene (A). On applying the same treatment to eudesmol and selinene they obtained, with the elimination of a Me group, in the dehydrogenation, another C10H8 hydrocarbon d. 0.973, b. 280┬░, MD 63.31┬░, and called it eudalene (B). It was found that all the sesquiterpenes from a single plant source gave either all A or B, but never mixtures. Both A and B are satd. towards Br and cold KMnO4. The constitution of A has been fixed by synthesis (cf. following abstr.) as 1,6-dimethyl-4-isopropylnaphthalene. It was found to be readily oxidized by H2CrO4, yielding 1,6-dimethyl-4-isopropylnaphthoquinone, whose oxime m. 178┬░, and 6-methyl-4-isopropyl-1-naphthoic acid, m. 161-2┬░, besides some unidentified products. Semmler (Ber. 47, 2555) has shown from work on copaene (tricyclic), which gives cadinene dihydrochloride with HCl, that the double bond in cadinene must be in the following position:. R. et al., have found that the monocyclic terpene zingiberene (C) gave with S the C10H8 hydrocarbon A. Semmler (Ber. 46, 1814) had already shown that C gave with acids the bicyclic isozingiberene. Thus the formation of A on treatment with S is not sure proof of the existence of the C10H8 configuration in the original hydrocarbon. But since A can be obtained from mono-, di-, and tricyclic sesquiterpenes it must be regarded as bearing the same relation to them that p-cymene coes to the normal terpenes. The basic principle of all the structures is the co.ovrddot.ordination of isoprene residues, rubber being the highest polyterpene. [on SciFinder(R)]