Preparation and absolute configuration of (-)-(E)-α-trans-bergamotenone

The synthesis, absolute configuration, and olfactive evaluation of (-)-(E)-alpha-trans-bergamotenone (=(-)-(1'S,6'R,E)-5-(2',6'-dimethylbicyclo[3.1.1]hept-2'-en-6'-yl)pent-3-en-2-one; (-)-1), as well as its homologue (-)-19 are reported. The previously arbitrarily attributed absolute configuration of 1 and of (-)-alpha-trans-bergamotene (=(-)-(1S,6R)-2,6-dimethyl-6-(4-methylpent-3-enyl)bicyclo[3.1.1]hept-2-ene; (-)-2), together with those of the structurally related aldehydes (-)-3a,b and alcohols (-)-4a,b, have been rigorously assigned.