SYNTHETIC STUDIES ON CLERODANE DITERPENOI DS - A CASE OF THE STEREOCONTROLS IN NATURAL-PRODUCTS SYNTHESIS

Synthetic studies on the clerodane diterpenoids, a rapidly growing gro up of natural products, are reviewed from the standpoint of stereocont rols for the construction of a unique four contiguous stereogenic cent ers on their bicyclic skeleton. Strategies for the clearance of the st ereochemical problems are described according to the types of major st ereochemical features-namely trans and cis with respects to the ring f usion, and cis and trans disposition of C1-unit at C-8 and C-9 positio ns. The description involves the methods for enantioselective synthesi s. Brief mentions are made on the synthetic methods for the related na tural products (sesqui-, di- and sesterditerpenoids) with ''clerodane' ' skeleton or substitution (hence with common problems of the stereoco ntrol) and on the investigations for the construction of the specific groupings in bioactive clerodane diterpenoids. The preliminary approac hes as well as the methods used in the successful total synthesis are introduced in the modern light of stereocontrols.