DEVELOPMENTS IN THE CHEMISTRY OF IONONES 445 oxide C13HO24 (Fig. 22) corresponds), the pyranose form of cis-•-ionone (Fig. 17), ionene (Fig. 23) (113, 114). the tricydo-ionone isolated by Naves and Bachmann (115) and described structurally by Btichi et al (116) (Fig. 24). This latter is derived from cis-pseudo-ionone (nerylidene-acetone), and sulphuric acid at 0 ø converts it to a dihydro-pyran. Figure 20 Figure oe1 a o Figure 21 b Figure 22 Figure 23 Figure 24 The action of titanium tetrachloride on the cyclization has been studied especially (116--119). Starting from cis-pseudo-ionone, but not from trans, chlorination products are formed from which, after treatment with collidine, two epimeric bicyclo-ionones are obtained (6% of Fig. 25a and 32% of Fig. 25b) alongside minor proportions of a- and [l-ionones. Vanadium pentachloride gives the same result. Boron trifluoride gives rise to neither bicyclo- nor tricyclo-ionones. Some ionone derivatives are used in the flavouring of tobacco. Epoxidation of [l-ionone gives 2-hydroxy-a-ionone (120) (Fig. 2fi), whose 5-oxo derivative (Fig. 27) is obtained by treating a-ionone with tertiary-butyl chromate in boiling tertiary-butyl alcohol, whilst oxidation in a non-polar solvent such as boiling benzene gives 5-oxo-ionone (66).

446 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS Dehydro-13-ionone is prepared from the dibromo derivative of a-ionone by the agency of a tertiary nitrogenous base (121). The photo-oxidation',iof •-ionone has been studied by Mousseron-Canet et al (38). The peroxide Figure oe5a Figure oe$b Figure 28 Figure formed (Fig. oe8) is re-arranged by a basic reagent and mainly Figs. oe9, $Oa (which leads to dihydro-actinidiolide (Fig. $1)), $oea, $oeb, and $$ are ob- tained. Figure oe8 Figure ,••0 0• ø Figure 30 Figure $1 Figure $•a Figure ...•.i• ø oE Figure 38 Several interesting products have been prepared from dihydro-ionones and ionols.