Catalytic alkene isomerization is a powerful synthetic strategy for preparing valuable internal alkenes from simple feedstocks. The utility of olefin isomerization hinges on the ability to control both positional and stereoisomerism to access a single product among numerous potential isomers. Within base-metal catalysis, relatively little is known about how to modulate reactivity and selectivity with group-6 metal-catalyzed isomerization. Here, we describe a tungsten-catalyzed, positionally selective alkene isomerization reaction in which tuning the ligand environment grants access to either the E- or Z-stereoisomer. The reactions employ simple, commercially available precatalysts and ligands. Preliminary mechanistic studies suggest that the ligand environment around 7-coordinate tungsten is crucial for stereoselectivity, and that substrate directivity prevents over-isomerization to the conjugated alkene. These features allow for exclusive formation of β,γ-unsaturated carbonyl compounds that are otherwise difficult to prepare.

中文翻译：

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钨催化的末端烯烃的立体发散异构化


催化烯烃异构化是一种强大的合成策略，用于从简单原料制备有价值的内部烯烃。烯烃异构化的效用取决于控制位置异构和立体异构的能力，以便在众多潜在异构体中获得单一产品。在贱金属催化中，关于如何用 6 族金属催化的异构化来调节反应性和选择性，人们知之甚少。在这里，我们描述了一种钨催化的、位置选择性烯烃异构化反应，其中调节配体环境允许获得 E 或 Z 立体异构体。这些反应采用简单的市售预催化剂和配体。初步机理研究表明，围绕 7 配位钨的配体环境对于立体选择性至关重要，并且底物方向性可防止共轭烯的过度异构化。这些特性允许专门形成 β，γ-不饱和羰基化合物，否则这些化合物很难制备。