SESQUITERPENES IN THE PERFUMERY INDUSTRY 215 quality, vetiver oils contain 45-65•o free sesquiterpene alcohols bicyclo- and tricyclovetivenols. The commercial product is a mixture of these two vetivenols and has a warm, sweet, mildly earthy-balsamic and extremely tenacious odour. These alcohols blend well with ionones, styrax, sandalwood and various materials for oriental and woody bases or perfumes (13). The corresponding aldehydes are known to have an olibanum type odour. The mixed acetates obtained by the acetylafion of the above alcohols or by isolation from essential oil are sold under several trade names. The sweet- dry, fresh-woody odour with excellent tenacity allows its use in all types of perfumes (13 ). Longifolene, a hydrocarbon belonging to the longifolane group, is one of the few sesquiterpenes commercially available in quantity. Much interest has been shown by the industry in the new materials that chemical in- vestigation into longifolene chemistry has presented to the perfumer. Longifolene was first isolated by Simonsen (59) from Pinus longifolia and the search for commercial uses for the hydrocarbon extends back 50 years. The structure was established by Moffett (60) and Ourisson (61) and commercial exploitation has followed this breakthrough. The structure of longifolene has been confirmed by a total synthesis (62) but such syntheses are of academic interest only. Two simple longifolene derivatives are on the perfumer's shelf at the moment: acetyl longifolene and hydroxymethyl longifolene. Acetyl longi- folene (63) is prepared by the Friedel-Crafts reaction and has a woody- musky ambergris odour reminiscent of acetyl cedrene. Longifolene Figure 18. Acetyl Iongifolene The Prins reaction has been of use in the production of perfumery chemicals from monoterpenes (Nopol, Patchenol) and application of this reaction to longifolene produces to-hydroxymethyl longifolene (64, 65). This alcohol is of use in perfumery. The simple methods of longifolene oxidation yield complex mixtures with sesquiterpene acids predominating (66). Direct oxidation of longifolene has not been of great commercial interest. Formylation reactions have been

216 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS Longifolene (I) HCHO AcOH (2)NaOH Figure 19. ••CH20 H' t•-- Hydroxymethy I Io ng ifolen e of recent interest in the production of new monoterpene perfumery chemi- cals (67-69), e.g. dihydromyrcene cyclic esters. Application of these reaction conditions to longifolene produces longibornan-9-ol formed by rearrange- ment and transannular hydride shift (70). A recent patent claims this formate to be of value in perfumery (71). •\\ o II (I) HCOH (2) NeOH Long i fol ene Longiborna n-9-ol Longifolene Isolongifolene Figure 20. Early attempts at longifolene acetoxylation did not give good yields of acetates but an isomer of longifolene was produced called isolongifolene (72). The structure of isolongifolene was established by Ranganathan et al. (73) who later completed a total synthesis of the hydrocarbon (74). [solongifolene has proved to be of more commercial interest than longifolene as simple methods of oxidation yield non-acidic products. If longifolene or isolongifolene are treated with zinc chloride at high temperatures then 1,1-dimethyl-7-isopropyltetralin is formed (75). Acetyla- tion of this tetralin gives the methyl ketones these are said to have a fine although weak musk odour. The aldehydes have a stronger musk odour but the propionyl compound is odourless (75). Epoxidation of isolongifolene with peracids yields the •z-epoxide (76). This epoxide is of little perfumery interest but rearrangement of the epoxide produces the saturated ketone 8-oxo-7-13-H-isolongifolane which has a desirable woody odour and has found use in perfumery. Epimerization of