Synthetic Studies on Aphidicolane and Stemodane Diterpenes. V. A Facile Formal Total Synthesis of (.+-.)-Aphidicolin via a Lewis Acid-Mediated Stereoselective Spiroannelation.
作者:Tetsuaki TANAKA、Osamu OKUDA、Kazuo MURAKAMI、Hitoshi YOSHINO、Hidenori MIKAMIYAMA、Atsushi KANDA、Sang-Wong KIM、Chuzo IWATA
DOI:10.1248/cpb.43.1407
日期:——
Formal total synthesis of (±)-aphidicolin (1) was achieved via a Lewis acid-mediated stereoselective spiroannelation reaction as a key step. The bisbenzyl acetal (2) was synthesized from the readily available dimethyl acetal (4). Treatment of 2 with trimethylsilyl trifluoromethanesulfonate (TMSOTf) afforded a 69 : 31 mixture of the spirocyclic enones (9 and 10) in excellent yield. The tricyclic ketal-ketone (3) corresponding to the B/C/D rings of 1 was easily generated from the enone (9) by intramolecular alkylation and catalytic hydrogenation as principal steps. The A-ring construction was performed by a procedure similar to one used previously. Barbier reaction of 14, followed by oxidative rearrangement, stereoselective 1, 4-addition of a methyl group, and subsequent intramolecular aldol-condensation afforded the tetracyclic enone (18), which has already been transformed into (±)-aphidicolin (1).
通过路易斯酸介导的立体选择性螺环化反应,实现了(±)-蚜腈(1)的正式全合成,这是关键步骤。双苄基缩醛(2)由易得的二甲基缩醛(4)合成。用三甲基硅基三氟甲磺酸酯(TMSOTf)处理2,得到69:31的螺环烯酮(9和10)混合物,收率很高。通过分子内烷基化和催化氢化作为主要步骤,很容易从烯酮(9)生成与1的B/C/D环相对应的三环缩酮(3)。A环的结构通过类似于先前使用的程序进行。14的巴比尔反应,然后是氧化重排,甲基的立体选择性1,4加成,以及随后的分子内醛缩合,得到四环烯酮(18),它已经转化为(±)-蚜腈(1)。