38 新不活性C-H結合攻撃法と,そのEnmeinよりGibberellin A_<15>合成への応用
詳細
We have attempted the synthesis of Aconit-Alkaloids and Gibberellins from Enmein (1). The most important point is how to functionalize the non-activated C_<19>-methyl group of Enmein. We have many methods for attacking non-activated C-H bond, our trials by these methods did not success, for example, the photolysis of acylazide(2), etc. On our hypothesis that the C_<19>-methyl shoud be attacked by the photolysis of some nitrone, we finally irradiated the nitrone (18), which had been derived from Enmein. The nitrone(18) afforded the expected product (20), formed by attack on the C_<19>-methyl, and another compound (21). Yields of (20) and (21) under various conditions were examined and the results were explained by some possible mechanisms, a) and b). We propose the photolysis of nitrone as a novel method for attacking non-activated C-H bond. The compound (20) was isomerized to imine (27). The ring system of (27) was converted to Gibbane-skeleton treated with HNO_2. Immediate oxidation of the products mixture afforded the compounds (29) and (30). The compounds (29) and (30) were reduced, mesylated and demesylated to give the products (35) and (36), which were refluxed with KOH in abs. D.E.G to afford iso-GA_<15> (38) and GA_<15> (39). The compound (39) was identical with natural Gibberellin A_<15> in every respects.
