I Synthesis of α-Chamigrene On the assumption that Chamigrenes (3,4) could be obtained by dehydration and simultaneous cyclization of cis-and trans-monocyclofarnesol (2b,2a), 2a and 2b were treated with iodine in benzene solution and 4 was actually isolated from the reaction mixture with 25% yield. II Cyclization of Monocyclofarnesic Acid In order to obtain the optimum conditions in the acid-catalyzed cyclization of β-monocyclofarnesic acid (10) to α-bicyclofarnesic acid (11), an intermediate which is expected to be of use in synthesis of drimenins(21,22) and levantenolides (32,33), 10 was treated with gaseous boron trifluoride in benzene solution and a new cyclization product (12), an isomer of 11, was isolated. The structure of 12 was determined by chemical degradation and their nmr spectra (table 1). By treatment of 10 with a BF_3-saturated solution of Et_2O-C_6H_6(1: 5) (30°, 24hr), the yield of purified 11 from 10 was improved and increased by up to 55%. III Synthesis of Drimenin The methyl ester (25) was photo-oxidized and the peroxides were reduced (KI) to afford the mixture of hydroxy-esters (26), (27) and oxo-ester (28) which were separated by SiO_2 chromatography. Hydrolysis and simultaneous lactonization of 26 gave the mixture of drimenin (21) and isodrimenin (22). Synthetic approach of polygodial (24) is now under investigation using 30 and 31 which were obtained from 21 by LiAlH_4-reduction. IV Synthetic approach of Levantenolides. 34 was obtained by photo-oxidation of 36 which was derived from 35 and 2,2-Di-3-methylfurylmercury. Cyclization of 34 to levantenolides are being investigated.
