ABC-ring 6 by detaching the three-carbon units and the oxygen-appended groups. Intermediate 6 with six stereocenters was assembled from four achiral fragments in 12 steps by integrating three powerful transformations, as follows: (i) asymmetric Diels–Alder reaction to induce formation of the C-ring; (ii) π-allyl Stille coupling reaction to set the trisubstituted E-olefin of the B-ring; and (iii) Eu(fod)3-promoted
Asymmetric Total Synthesis of Crotophorbolone: Construction of the 5/7/6-Fused Ring System via an α-Alkoxy Bridgehead Radical Reaction
作者:Daisuke Urabe、Taro Asaba、Masayuki Inoue
DOI:10.1246/bcsj.20160208
日期:2016.10.15
of a synthetic route to crotophorbolone (1). Compound 1 is classified as a derivative of the tigliane diterpenoids, and possesses a highly oxygenated 5/7/6-fused ABC-ring system. First, the six-membered C-ring fragment with five contiguous stereocenters was stereoselectively constructed from (R)-carvone. Nucleophilic addition of the three-carbon unit to the C-ring and stereoselective attachment of the
该帐户描述了克罗托佛酮 (1) 合成路线的开发。化合物 1 被归类为 tigliane 二萜类化合物的衍生物,具有高度氧化的 5/7/6 稠合 ABC 环系统。首先,具有五个连续立体中心的六元 C 环片段是由 (R)-香芹酮立体选择性构建的。三碳单元与 C 环的亲核加成和五元 A 环的立体选择性连接通过 π-烯丙基斯蒂尔偶联反应提供了关键自由基环化的底物。接下来,在回流甲苯中用 V-40 和 (TMS)3SiH 处理 O,Se-缩醛产生 α-烷氧基桥头自由基,其参与七元 B 环的内环化,形成空间位阻C9-立体特异性和C10-立体选择性方式中的拥挤键。
On the Development of Catalytic Carba-6π Electrocyclizations
Hexatriene substrates substituted in the 2-position with carbonyl groups were studied in the context of catalytic 6p electrocyclizations. The nature of the carbonyl group and the substitution pattern on the hexatriene have significant effects on the ability of these substrates to succumb to catalysis. A novel 2-formyl hexatriene dimerization was observed. The first example of a catalytic asymmetric carba-6p electrocyclization is reported along with the discovery of an unusual kinetic resolution via a catalytic photochemical electrocyclic ring-opening.