ODOR AND ISOMERISM IN OLFACTIVE CHEMICALS 267 the isomeric species. This was indeed achieved by taking advantage of the greater thermal stability of the cis-isomer. This conversion was easily followed by observing the reversal of the optical rotation of the dextro-trans isomer (aD = +44 ø) into the levo-cis-isomer (aD = --133ø). Some irreversible formation of the fi-isomer as a by-product of the trans- cis-arrangement was accompanied by loss of optical activity through racemization resulting from the migration of the alkene bond. Here again, as in the ionone series, the •-Nerone isomer did not possess an odor of particular interest. A similar type of spatial cis-trans isomerism occurs in rosenoxide present in rose and geranium oils (17). As in the case of Nerone this isomerism is the result of a cis-trans spatial configuration of the 2,4 substituents of the tetrahydropyrane ring. LEAF ALCOHOL "C5 cm trans (XXI) (xix) (xx) The cis-isomer (XIX) which is the major component (80-85%) of the natural rosenoxide happens to possess the finest odor characteristics. By analogy with parent cyclohexane derivatives the conformational analysis of this meta substituted tetrahydro pyrane assigns its substituents (methyl and methylpropenyl groups) to the equatorial position for a most stable cis-configuration. Other double-bond isomers of rosenoxide (XXI), and in particular the vinyl ether isomers, show little olfactive value unless readily converted to cis-rosenoxide. Finally, leaf alcohol, a valuable component in violet compositions, illustrates the last case of a typical alkene (cis-trans) isomerism (group 4). Ever since the olfactive importance of leaf alcohol, cis-hex-3-en-l-ol (XXII), was recognized its structure was the subject of intensive research (18) which culminated in its preparation. Its synthesis was achieved by Stohl, Sondheimer and other workers (19) through the selective palladium hydrogenation of the corresponding hex-3-. yn-l-ol (XXIII). The latter was obtained through the condensation of 1-butyne sodium with ethylene oxide. The trans-hex-3-en-l-ol (XXI¾) obtained by the sodium/liquid ammonia reduction of the corresponding hexynol has no great olfactive value and does not possess the green leafy fragrance almost indispensable in violet compositions. The theoretical and practical benefits derived from the knowledge gained through the stereochemical studies of olfactive substances is obvious. The

268 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS O I 4- /\ Na ROSENOXIDES Hex-3-en-l-ol , [l• c)H (xxttt) H•/Pd [ Naliq. NH• cis trans (XXII) (XXIV) proper use of sophisticated instrumentation in the field of gasAiquid chromatography, nuclear magnetic resonance, infrared and ultraviolet spectroscopy, coupled with the necessity of devising ingeneous stereo- specific syntheses, constitute a constant challenge exciting to meet for those active in the field of research in o]factive chemicals. (Received April 5, 1963) REFEKENCES (1) Proc. Sci. Sect. Toilet Goods Atssoc., 36, Suppl. No. 37 (1962). (2) E.H. Eschinasi, GivaudanJan, p. 3 (Oct. 1959) U.S. Patent No. 3,007,961 (1961). (3) P. Barbier and R. Loquin, Cornpt. Rend. Atcad. Sci., 157, 1114 (1913). (4) A. Verley, Bull. Soc. CAirn. France (4),45, 845, 854 (1928). (5) V. Grignard andJ. Doeuvre, Ibid. (4) 45, 809 (1929). (6) M. F. Carroll, R. G. Mason, H. W. Thompson and R. C. S. Wood, y. Chern. Soc., 3457 (1950) U.S. Patent No. 2,902,495 (1959). (7) Y. R. Naves et al., Cornpt. Rend. Atcad. Sci., 200, 1112 (1935) Y. R. Naves, Bull. Soc. Chirn. France (5), 18, 505 (1951). (8) J. L. Simmonsen, The Terpenes, Vol. I, pp. 35, 37, 73, 74, 75, 80, University Press, Cambridge (1947). (9) E.H. Eschinasi, 5 t. Org. Chem., 26, 3072 (1961). (10) Y. R. Naves, D. Lamparsky and P. Ochsner, Bull. Soc. Chim. Prance (5), 28, 645 (1961) A. Melera and Y. R. Naves, Cornpt. Rend. ztcad. Sci,, 252, 1937 (1961). (11) U.S. Patent No. 2,957,027 (1960). (12) German Patent No. 75,120 (1893). (13) U.S. Patent No. 2,517,576 (1950) Y. R. Naves et al., Bull. Soc. Chim. France (5), 20, 873 (1953). (14) Y. R. Naves, Heir Chirn. ztcta, $1, 1103 (1948) Bull. Soc. Chirn. France (5), 21,321,667 (1954) cf. also U.S. Patent Nos. 2,517,800 (1950), 2,517,576 (1950) Y. R. Naves in Molecular Structure and Organoleptic •uality Symp., Soc. Chern. Ind., p. 38, Geneva (1957). (15) Y.R. Naves, Heir. Chim. Atcta, 32, 969 (1949). (16) Y. R. Naves, Perfumery Essent. Oil Record, 40, 197 (1949) Bull. Soc. Chim. France (5), 25, 377 (1958). (17) C.F. Seidel et al., Helv. Chim. Atcta, 42, 1830 (1959) Ibid., 44, 598 (1961). (18) H. Walbaum, 5 t. prakt. Chem., 96, I I, 245 (1917) S. Takei et al., Ber., 68, 953 (1935). (19) M. Stohl and A. Rouve, Helv. Chim. •icta, 21, 1542 (1937) F. Sondheirner, 5 t Chern. Soc., 877 (1950) L. Crombieetal.,Ibid., 873 (1950).