Su.tnmai/y The spiroenone (7), stereoselectively prepared from (+)-p-menth-l-ene (3) in four steps, was converted by two different reaction sequences into the natural sesquiterpenes (-)-acorenone ( 1) and (-)-acorenone B (2), respectively, thus establishing the absolute configuration of (1).MUCH attention has been directed recently towards the development of new syntheses of the acoranes, a group of sesquiterpenes with a spiro [4.5]decane skeleton. We describe here a new route to (-)-acorenonel(1) and to (-)-acorenone B 2 p 3 (2), two members of the acorane family.Ozonolysis of ( +)-p-menth-l-ene4 (3) ( [ a ] g + log", G 1.1, CHC1,) in methanol, followed by reductive cleavage, gave a ketoaldehyde, which was cyclised5 (piperidine, AcOH, CHCl, reflux) to the ap-unsaturated aldehyde (4) (60% overall yield). The C=C double bond of (4) was hydrogenated (Pd-CaCO,, K,CO,, MeOH, H,O), as expected, on the side of the cyclopentane ring opposite to the isopropyl group ; after spontaneous epimerization, the trans,transcyclopentane derivative (5) was obtained 95% pure t(80y0 yield). The structure of (5) was confirmed by its identity with the hydrogenation product (PtO,, AcOEt) of trans,-
