Formal [2 + 2 + 2] cycloaddition strategy based on an intramolecular propargylic ene reaction/Diels-Alder cycloaddition cascade.
Formal [2 + 2 + 2] cycloaddition strategy based on an intramolecular propargylic ene reaction/Diels-Alder cycloaddition cascade.
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DOI：
10.1021/ja1053829
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发表时间：
2010-08-18
影响因子：
15
通讯作者：
Danheiser RL
中科院分区：
文献类型：
--
作者：
Robinson JM;Sakai T;Okano K;Kitawaki T;Danheiser RL
一个正式的，无金属，[2 + 2 + 2]环加成策略的基础上级联的两个周环过程。第一步涉及1，6-二炔的分子内炔丙基烯反应以生成乙烯基丙二烯，然后乙烯基丙二烯在分子间或分子内Diels-Alder反应中与烯基或炔基亲二烯体反应。涉及不对称烯基和炔基亲二烯体的反应以良好至优异的区域选择性进行，并且在Diels-Alder步骤中的非对映选择性也很高，其中产生的内环加合物作为反应的唯一产物。在炔基亲二烯体的情况下，[4 + 2]环加成最初产生异甲苯型中间体，其在室温下暴露于催化量的DBU时异构化为分离的芳族产物。几个早期的完全分子内相关的转换机制已被证明涉及一个类似的过程，而不是以前提出的双自由基介导的途径。
A formal, metal-free, [2 + 2 + 2] cycloaddition strategy is described based on a cascade of two pericyclic processes. The first step involves an intramolecular propargylic ene reaction of a 1,6-diyne to generate a vinylallene, which then reacts in an inter-or intramolecular Diels-Alder reaction with an alkenyl or alkynyl dienophile. Reactions involving unsymmetrical alkenyl and alkynyl dienophiles proceed with good to excellent regioselectivity, and the diastereoselectivity in the Diels-Alder step is also high, with endo cycloadducts produced as the exclusive products of the reaction. In the case of alkynyl dienophiles, [4 + 2] cycloaddition initially generates an isotoluene-type intermediate that isomerizes to the isolated aromatic product upon exposure to a catalytic amount of DBU at room temperature. The mechanism of several earlier fully intramolecular related transformations have been shown to involve an analogous process rather than the diradical-mediated pathways proposed previously.
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影响因子：
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