Chemistry of (+)-aromadendrene. Part 6: Rearrangement reactions of ledene, isoledene and their epoxides

The chemistry of (+)-ledene and (−)-isoledene, both easily available from (+)-aromadendrene has been investigated. Reactions at the double bond of ledene take place preferably from the β-side. Under acidic conditions its C7–C8 β-epoxide and β-diol preferably react via carbocations, which are initially formed at C8. Rearrangement takes place to compounds with cubebane and cadinane skeletons. The reaction pattern of isoledene and its α-epoxide, under acidic conditions, is governed by the easy formation of an intermediate α-cyclopropylcarbinyl carbocation. Further reactions lead to products in which the C2–C3 bond of the cyclopropane ring is broken to give compounds with a guaiane skeleton. Guaiane-type dienes and unsaturated cyclic ethers are the final products of these rearrangements. Several derivatives of these compounds have been prepared.