Synthetic Studies of Cotylenol, Having Plant Growth Activity, and the Related Biogenetically Active Terpenoids.

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1. It has been proved that a diterpenoid named sordaricin (1) is biosynthesized from its congener, hydroxycycloaraneosene (2). From the structural relationships between 1 and 2, the biogenesis of 1 must involve an oxidative ring-fission of the central 8-membered ring of 2 followed by an intra-molecular Diels-Alder reaction of resulted cyclopentadiene and unsaturated aldehyde moieties. The synthetic studies utilizing of this Diels-Alder reaction have accomplished the first total synthesis of methyl ester derivative of 1.2. The total synthesis of fusicocca-2,5-diene (3), a 5-8-5-membered tricyclic diterpene, has been accomplished. Although 3 has not been isolated yet, several terpenoids are considered to be biosynthesized from 3. Plagiospilolides A and B (4,5), metabolites of the liverwort, are the Diels-Alder products from 3 and the sesquiterpene lactones, diplophyllolide (6) and diplophyllin (7), respectively. In fact, the Diels-Alder reactions between 3 and totally synthesized 6 and 7 gave 4 and 5, respectively, with high stereoselectivities. With this total synthesis, the absolute configurations of 4 and 5 have been deduced.3. A synthetic problem for the total synthesis of cotylenol (8) laid in the control of the stereochemistry of an 8,9-glycol moiety. To overcome this problem, two synthetic routes were investigated. Although the reductive cyclization of dial-precursors failed to control the stereochemistries of this glycol function, the 'ene'-cyclization procedure gave several encouraging results. The later process has provided not only the method of controlling the stereochemistries but also the method of converting 3-hydroxyl group, which is deeply related with an instability of 8, to a thiol moiety.