南开大学资伟伟团队介绍了Lewis酸促进配体控制的Pd氧烯丙基与13二烯环加成反应的反应发展和选择性的起源。 相关研究成果于2021年2月25日发表在《美国化学会杂志》。

近30年来，Pd-氧烯丙基与烯烃的催化（3+2）环加成反应一直是研究的热点。然而，由于C–O键的形成在动力学上具有优势，迄今为止（3+2）环加成反应仍涉及C–O还原消除。

该文报道了一种三氟化锂促进Pd-氧烯丙基物种与1,3-二烯的（3+2）环加成反应的方法，该反应通过以C–C键形成终止的途径进行，从而得到五元碳环。该反应中通过Li离子和烷氧基结构配位，影响C-O键还原消除，形成金属-烯醇盐连接的π-烯丙基-Pd物种中间体，随后π-烯丙基-Pd通过烯醇的分子内烯丙基进攻生成碳环产物。

此外，通过调整钯配体的空间位阻性质，还可以完成竞争性的（4+3）环加成反应，因此该方法提供了环戊酮和环庚酮的区域性途径。通过DFT计算研究了反应机理，并对环加成反应区域选择性的来源进行了合理的解释。

附：英文原文

Title: Lewis-Acid-Promoted Ligand-Controlled Regiodivergent Cycloaddition of Pd-Oxyallyl with 1,3-Dienes: Reaction Development and Origins of Selectivities

Author: Weiwei Chai, Qingyang Zhou, Wenna Ai, Yin Zheng, Tianzhu Qin, Xiufang Xu, Weiwei Zi

Issue&Volume: February 25, 2021

Abstract: 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 π-allyl-Pd. The π-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.

DOI: 10.1021/jacs.0c13412

Source: https://pubs.acs.org/doi/10.1021/jacs.0c13412