5 (±)-Antheridiogen-Anの全合成(口頭発表の部)

概要

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Antheridiogen-An (A-An, 2) is a plant hormone which stimulates sex-organ development and spore germination in fern. The gibberellin-related structure was elucidated by Nakanishi et al. in 1971, and later the configuration at the C(3) position was corrected by the total synthesis of A-An by Corey et al. Here, we wish to report the total synthesis of A-An in a highly stereocontrolled manner. Hydrofluorene lactone 5 was prepared from diene 6 via acid anhydride 7 and keto acid 8 (Scheme 1). Lactone 5 was then converted into δ-lactone 28 (A/B cis) (Scheme 4). Saponification of 28 gave the carboxylate, which was subjected to Birch reduction followed by successive thioketalization and MCPBA oxidation giving sulfoxide 31. Thermolysis of 31 in the presence of diisopropylethylamine followed by Diels-Alder reaction with 2-chloroacrylonitrile gave bicyclo[2.2.2]octane derivative 32. Exo-olefin 34 having a carbon skeleton of A-An was synthesized from 32 by following sequence: i) stepwise reduction of the cyano group; ii) acetylation, iii) Li-liq.NH_3 reduction to give 33, iv) acetylation; and v) Li-liq.NH_3 reduction. The secondary hydroxyl group at C(1) in 34 was removed via 35 having C(1)-α-OH to give 36, whose acetal was easily hydrolyzed to afford aldehyde 37. Synthesis of (±)-antheridiogen-An was accomplished by elaborative adjustment of functionality of A ring in 37 (Scheme 5).
天然有機化合物討論会の論文
1991-09-07