Umpolung of pi-Allylpalladium with Diethylzinc and Synthetic Application

烯丙基钯通常被认为是许多亲核试剂（有机金属）合成的重要的亲电烯丙化剂。本研究从机理上阐明了烯丙基酯与Pd(O)在原位催化反应生成的pi-烯丙基钯配合物与二乙基锌进行烷基配体交换，得到烯丙基锌和二乙基钯的混合物。由此形成的烯丙基锌在与羰基化合物的反应中表现出独特的区域选择性和立体选择性。例如，1,3-二取代烯丙基锌与醛反应生成具有高立体选择性的(Z)-抗同丙基醇。此外，本方法对于生成具有立体化学定义的烯丙基锌是非常有用和强大的，这是其他方法很难生成的。在丙烯基钯和三乙基硼烷之间进行了类似的非pollung反应（未发表的结果）。在相关研究中，证明了pi-烯丙基钯是促进β -脱碳反应的活性物质。该反应也催化钯，并提供-二烯醛和酮在良好的产量。《化学与工程新闻》从以下几个方面摘录了这篇报道；反应类型的独特性和产物作为合成中间体的合成重要性。

pi-Allylpalladium is usually recognized to serve as synthetically important electrophilic allylating agent toward many nucleophiles (organometals). This research mechanistically clarified that pi-allylpalladium complexes, catalytically generated in situ by the reaction of allylic esters and Pd(O), undergo the alkyl ligand exchange with diethylzinc and provide a mixture of allylzinc and diethylpalladium species. The thus formed allylzinc demonstrated unique regio-and stereoselectivity for the reaction with carbonyl compounds. For example, 1,3-disubstituted allylzinc reacted with aldehyde to provide (Z)-anti-homoallyl alcohols with high stereoselectivity. Furthermore, the present methodology turned out to be very useful and powerful to generate stereochemically defined allylzinc species, the species being very difficult to generate by other methods. The similar umpolung reaction proceeds between pi-allylpalladium and triethylborane (unpublished results).In the related research, it was demonstrated that pi-allylpalladium serves as an active species to promote beta-decarbopalladation reaction. This reaction also proceeds catalytically with respect to palladium and furnishes omega-dienyl aldehydes and ketones in good yields. Chemical & Engineering News picked up this report from the following points of view ; the uniqueness of the reaction type and the synthetic importance of the products as synthetic intermediates.