STUDIES DIRECTED TOWARD THE TOTAL SYNTHESIS OF KALMANOL - AN APPROACH TO CONSTRUCTION OF THE C/D DIQUINANE SUBSTRUCTURE

A retrosynthetic scheme for the total synthesis of kalmanol is discussed. This analysis has as its basis the implementation of a Tebbe-Claisen sequence for establishing the entire structural framework of the diterpenoid. Arrival at this advanced stage requires the availability of a suitable stereoisomer of the functionalized diquinane 5. Described herein is an approach to this key building block that is based on adaptation of the Pauson-Khand reaction. In light of the preliminary nature of the study, the various chiral intermediates have been produced only in racemic condition. Nevertheless, the level of stereocontrol associated with this sequence for the elaboration of 5 is high, thereby setting the stage for an apparently serviceable entry into the A-homo-B-nor grayanoid backbone that is uniquely characteristic of the target compound.