New Strategy toward clerodanes synthesis

Clerodanes diterpenes have been considerably studied by biologists and chemists, according to their interesting antifeedant activity on insects as well as their unique structure, which make them a challenging target for total synthesis. Several problems related to their synthesis have been solved1,2,3, and some natural products have been synthesised in the ajugarin's series4 as well as in the dehydroclerodanes 4c. However, the problem of the stereoselective construction of the acyclic C-9-C-115 double bond, drastically related to this of the stereochemical control of stereogenic centers C-8, C-10 and C-5 remains up to date. We have developped two stategies aimed to this goal. Both strategies consist in controlling the configurations of some of the stereogenic centers of the target molecule in an early bicyclic structure easy accessible. One of the ring of these precursors should prefigurate the B ring of the clerodanes, the cleavage of the other ring giving access to functionnalized side chains which should allow the further elaboration of either the decalinic moeity of the molecule or the furofuran system through well known methodologies.