Ambergris fragrance compounds from labdanolic acid and larixol

Since ancient times, ambergris has been one of the most highly valued perfumery materials. Ambergris is a metabolic product of the spermwhale ( Physeter macrocephalus L.), which accumulates as concretions in the gut. (-)-AmbroxÒ, the commercially most important constituent of natural ambergris, is recognized as the prototype of all ambergris odorants. For this reason, various synthetic routes to (-)-AmbroxÒand its racemate have been developed, preferrably starting from cheap, abundantly available natural labdanes. Sclareol is nowadays the industrially used starting material for the preparation of (-)-AmbroxÒ. Labdanolic acid and larixol are both easily and abundantly available from labdanum gum of Cistus ladaniferus L. ("Rock-rose") and turpentine of the Larix decidua , respectively, but have found little use as starting material in syntheses of Ambergris odour compounds. In this thesis new chemistry in that field is described.From the acetate of labdanolic acid short procedures are developed for the synthesis of AmbroxÒ. Also a standard method has been developed for the oxidation of the side chain of several labdanes. Generally good to high yields of single products can be obtained using anhydrous potassium permanganate in the presence of a phase-transfer catalyst. In this way larixol can be converted into suitable synthons for the synthesis of several Ambrox-like compounds. 6a-hydroxy Ambrox can be considered to be a key intermediate in such syntheses and conversions of larixol into this intermediate are described. From 6a-hydroxy Ambrox a number of simple Ambrox derivatives have been synthesized. By heating with acid a mixture was formed consisting ofD5- andD6-Ambroxene, which both are pleasant smelling.D5-Ambroxene was produced in a more selective way by elimination of methanesulfonic acid from the corresponding mesylate of 6a-hydroxy Ambrox. A selective synthesis ofD6-Ambroxene proved to be more difficult and laborious. Several approaches were investigated, and ultimately the one via ringclosure of an allylic alcohol proved to give good results. It turned out that this new approach could not be extended to the selective synthesis of six-membered cyclic ethers, e.g.D6-Ambra oxides. In the latter case, elimination of the 6b-hydroxyl group to the correspondingD6,8-dienes was observed as the major reaction.