Lewis-Acid-Promoted Ligand-Controlled Regiodivergent Cycloaddition of Pd-Oxyallyl with 1,3-Dienes: Reaction Development and Origins of Selectivities
Lewis-Acid-Promoted Ligand-Controlled Regiodivergent Cycloaddition of Pd-Oxyallyl with 1,3-Dienes: Reaction Development and Origins of Selectivities
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DOI：
10.1021/jacs.0c13412
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发表时间：
2021-02-25
影响因子：
15
通讯作者：
Zi, Weiwei
中科院分区：
文献类型：
--
作者：
Chai, Weiwei;Zhou, Qingyang;Zi, Weiwei
近30年来，人们一直致力于开发钯-氧基烯丙基物种与烯烃的催化(3+2)环加成反应方法。然而，由于C-O键的形成在动力学上是有利的，到目前为止所实现的(3+2)环加成反应涉及C-O还原消除。在此，我们报道了一种三氟化锂促进的钯-氧烯丙基物种与1，3-二烯的(3+2)环加成反应，该反应通过一条以C-C键终止的途径进行，得到一个五元碳环。锂离子与烷氧基团的配位作用破坏了C-O还原消除反应，形成了金属烯醇基团的聚烯丙基钯。然后，pi-烯丙基-Pd部分接受来自烯醇基部分的分子内烯丙基攻击以形成碳环产品。此外，通过调节钯配体的空间性质，我们还可以完成竞争的(4+3)环加成反应，因此该方法提供了对环戊酮和环庚酮的区域发散访问。通过密度泛函理论计算，探讨了环加成反应的机理，并对环加成反应区域选择性的来源进行了合理的解释。
For nearly 30 years, considerable research effort has been focused on the development of methods for catalytic (3 + 2) cycloaddition reactions of palladium-oxyallyl species with alkenes. However, because C-O bond formation is kinetically favored, the (3 + 2) cycloadditions achieved to date have involved C-O reductive elimination. We herein report a method of lithium triflate-promoted (3 + 2) cycloaddition reactions of palladium-oxyallyl species with 1,3-dienes that proceed via a pathway terminated with C-C bond formation to give a five-membered carbocycle. Coordination of the lithium ion with the alkoxide moiety disrupts the C-O reductive elimination and forms a metal-enolate tethered pi-allyl-Pd. The pi-allyl-Pd moiety then accepts intramolecular allylic attack from the enolate moiety to form carbocyclic products. Furthermore, by tuning the steric properties of the palladium ligand, we could also accomplish the competing (4 + 3) cycloadditions, and thus this method provides regiodivergent access to both cyclopentanones and cycloheptanones. The reaction mechanism was investigated by DFT calculation and the origins of the regioselectivities of the cycloaddition were rationalized.