Introduction.
-Recently, Brunke and Schmaus presented the results of their analyses of sandalwood essential oil [l], and reported therein the discovery of a new constituent 1, present at the level of 0.01 %. This compound was identified by MS, IR, and 'Hand I3C-NMR analyses as a pent-3-en-2-one derived from the substructure of cc-trans-bergamotene (( -)-2; trans refers to the relation of Me-C(6) and CH,(7) with respect to the main ring of the bicycle structure) l ) . Due to the trace quantities isolated, the chiroptical data were not measured, and the olfactive properties, evaluated by GC sniffing, were found to be strongly milky, fatty, walnut, reminiscent of the top note of sandalwood essential oil ,). Dragoco's chemists also effected a partial synthesis, starting from a distillation fraction of sandalwood essential oil enriched in ( -)-(Z)-a-trans-bergamotenol (( -)-(Z)-4b; 32 % pure). Thus, MnO, oxidation afforded a mixture containing ( -)-(2)-3b3) [la] [6], whose autooxidation, in the presence of a catalytic amount of base (0.01 mol-equiv. of 'BuOK in 'BuOH [7]), afforded, apart from C=C isomerization to the (E)-diastereoisomer and degradation to norsesquiterpenoids, already described by Demole (nor-a-and nor-p-santalenone [S]) and Mookherjee (nor-epi-p-santalenone [9]), many other uncharacterized compounds, amongst which 1 (12 mg, 4.2%) was isolated.
The aldehyde (-)-(E)-3a (SeO,, 'BuOOH, EtOH, 78"; 26% from (-)-2; perspiration, woody [2]) was found in Suussureu luppu CLARKE [3]. The alcohol (-)-(E)-4a (LiAIH,, Et,O; 95% from (-)-(E)-3a [3]) exhibits animal top notes and woody, sandalwood notes. For earlier analyses of Suntalum essential oils, with identification of (-)-(Z)-4b (bright, somewhat woody, waxy, reminiscent of citrus afternote, highly diffusive), see [4]. Compound 1 was patented as a flavour (0.005 ppm) in a walnut aroma, as well as in perfumery compositions containing synthetic or natural sandalwood-like alcohols, to reinforce the fatty top notes [la]; its factor of dilution FD is 256. For comparison, the FD of (+)-(Z)-a-santalol and (-)-(Z)-b-santalol are 512 and 1024, respectively [I b]. For a selective synthesis of (-)-(Z)-3b from (-)-(Z)-4b, followed by chemical correlation with (-)-2 (aldehydic, orange, slightly conifer), see [4a] [5].