The preparation of the title compound (1), a key intermediate for the synthesis of helenanolides (pseudoguaianolides with a C10 α-methyl group), is described starting from the readily available enone (3). The correct stereochemistry of the C10-metyl group was obtained because of the severe 1, 3-diaxial interaction in the perhydroindanone (5). The ring expansion of 5 by one carbon unit, the key step in our approach, was examined in three ways. Reaction of 5 with ethyl diazoacetate catalyzed by a Lewis acid was not highly regioselective, giving the perhydroazulenone (8) and (9) in a ratio of 1 to 4. Metal salt-catalyzed decomposition of the diazoester (10) produced only the β-ketoester (11). However, the desired ketone (8) was obtained by the rearrangement of the β-oxido carbenoid derivative from the dibromohydrin (12). Introduction of the Δ6-double bond into 8 for the conversion to 1 was achieved regiospecifically via kinetic enolization.
描述了从容易获得的烯酮 (3) 开始制备标题化合物 (1) 的制备方法,标题化合物 (1) 是合成螺蛳醇内酯(具有 C10 α-甲基的假
愈创木酚内酯)的关键中间体。由于全氢
茚满酮中存在严重的 1, 3-二轴相互作用 (5),因此获得了 C10-甲基的正确立体
化学。 5×1 个碳单元的环扩展是我们方法中的关键步骤,通过三种方式进行了研究。 5 与重氮基
乙酸乙酯在
路易斯酸催化下的反应不具有高度区域选择性,以 1 比 4 的比例得到全氢薁酮 (8) 和 (9)。重氮酯 (10) 的
金属盐催化分解仅产生 β-
酮酯(11)。然而,所需的酮(8)是通过二
溴醇(12)重排β-氧化类
胡萝卜素衍
生物获得的。将Δ6-双键引入8以转化为1是通过动态烯醇化区域特异性实现的。