Asymmetric synthesis of allenyl oxindoles and spirooxindoles by a catalytic enantioselective Saucy-Marbet Claisen rearrangement.
Asymmetric synthesis of allenyl oxindoles and spirooxindoles by a catalytic enantioselective Saucy-Marbet Claisen rearrangement.
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DOI：
10.1002/anie.201107417
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发表时间：
2012-03-05
影响因子：
16.6
通讯作者：
Kozlowski, Marisa C.
中科院分区：
文献类型：
--
作者：
Trung Cao;Deitch, Joshua;Linton, Elizabeth C.;Kozlowski, Marisa C.
催化不对称Claisen重排反应的发展是有机合成中的一个长期挑战。[i]自该反应被发现以来的100多年里，仅报道了这种协同重排的五种高度对映选择性催化版本，依赖于刘易斯酸，[ii-iii]氢键催化剂[iv]或手性N-杂环卡宾。[v]还报道了通过π-烯丙基中间体的相关不对称转化。[vi]此外，在炔基乙烯基醚的重排中的对映选择性催化尚未被描述，即使辅助控制的非对映选择性版本被记载。[vii]在不对称催化中，这样的反应提出了一组独特的挑战，因为炔sp中心扭曲过渡态的几何形状和圆柱对称的炔提供没有机会的面部歧视。此外，这种重排的丙二烯基产物准备进行串联反应，以快速产生复杂的结构。本文报道了第一个不对称催化Saucy-Marbet Claisen重排反应，即炔丙基醚转化为β-取代的丙二烯基羰基化合物（方案1）。[viii]该反应通过串联重排产生两类含有新形成的季中心的手性羟吲哚：丙二烯基化合物和螺环内酯。[ix]随后的Saucy-Marbet Claisen重排的羟吲哚产物（4）是吲哚生物碱[x]结构中的中心结构单元，并且是药物制剂的有吸引力的平台。[xi]由于这些原因，催化不对称方法的发展，他们的产生一直是许多研究的主题。[3，xii]特别是，在C3处具有丙二烯基取代的对映体纯羟吲哚的形成尚未报道。
The development of catalytic enantioselective Claisen rearrangement reactions is a longstanding challenge in organic synthesis.[i] Only five highly enantioselective catalytic versions of this concerted rearrangement have been reported in the more than 100 years since this reaction was discovered, relying on Lewis acids,[ii–iii] hydrogen bonding catalysts [iv] or chiral N-heterocyclic carbenes.[v] A related asymmetric transformation via a π-allyl intermediate has also been reported.[vi] Furthermore, enantioselective catalysis in the rearrangements of alkynyl vinyl ethers has not been described, even though auxiliary controlled diastereoselective versions are documented.[vii] In asymmetric catalysis, such a reaction presents a distinct set of challenges since the alkyne sp centers distort the transition state geometries and the cylindrically symmetric alkyne provides no opportunity for facial discrimination. In addition, the allenyl products of such a rearrangement are poised to undergo tandem reactions to rapidly generate complex structures. We report here the first asymmetric catalytic Saucy-Marbet Claisen rearrangement, the transformation of propargyl ethers to provide β-substituted allenyl carbonyls (Scheme 1).[viii] The reaction gives rise to two classes of chiral oxindoles containing newly formed quaternary centers: allenyl compounds and spirocylic lactones via a tandem rearrangement.To start, we employed propargyl substituted indoles (3) which were obtained readily from 1 and 2 (Scheme 1).[ix] The oxindole products (4) of the subsequent Saucy-Marbet Claisen rearrangement are central building blocks in the construction of indole alkaloids [x] and are attractive platforms for pharmaceutical agents.[xi] For these reasons, the development of catalytic asymmetric methods for their generation has been the subject of much research.[3, xii] In particular, the formation of enantiopure oxindoles with allenyl substitution at C3 has not been reported.
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通讯作者：
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