Synthetic Studies on Polyquinane Sesquiterpenes

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Polyquinane framework plays an important role of structural unit of many kinds of naturally occurring organic compounds, some of which exhibit significantly biological activities. In this project, a couple of poluquinane sesquiterpenes were successfully synthesized by the use of a common intermediate 1 which was subjected to regioselective C-C bond cleavage of cyclopropane ring.The Birch reduction of 1 exclusively afforded the bicyclo 3.3.0 octane 2 via C_2-C_8 bond fission of the cyclopropane ring, while treatment of 1 under nucleophilic substitution conditions gave the bicyclo 3.2.1 octane 3 as a main product via the C_1-C_2 ond cleavage. On the other hand, the carboxylic acid 4, easily obtained from 1, afforded the lactone 5 efficiently through the exclusive C_1-C_2 bond fission by an intramolecular carboxylic acid participation.Through the several-step sequence starting from 2, total synthesis of a representative triqyinane sesquiterpene pentalenene (6) was accomplished.Descarboxyquadrone (7) and an antitumor diquinane sesquiterpene quardrone (9) were also synthesized by the use of key intermediates 3 and 8,respectively.