ETH Zurich, Vladimir-Prelog-Weg 3, HCI, 8093 Zurich, Switzerland.
Department of Chemistry, Korea Advanced Institute of Science and Technology (KAIST) and Center for Catalytic Hydrocarbon Functionalizations, Institute for Basic Science (IBS), Daejeon 34141, Republic of Korea.
J Am Chem Soc. 2021 Dec 29;143(51):21705-21712. doi: 10.1021/jacs.1c11528. Epub 2021 Dec 16.
The selective transition-metal-mediated activation of C(sp)-H bonds of allenes is a formidable challenge because of the competitive, intrinsic reactivity of cumulated double bonds. Herein, we report a Pd-catalyzed C-H alkenylation of electronically unbiased allenes, affording penta-1,2,4-triene products in up to 94% yield. A picolinamide directing group enables the formation of putative allenyl-palladacycles, which subsequently participate in a turnover-limiting Heck-type reaction with electron-deficient alkene coupling partners. This mechanistic proposal is consistent with experimental and computational investigations. Additionally, we report for the first time the use of picolinamide ,acetals as readily removable auxiliaries for C-H activation reactions, allowing the efficient alkenylation of allenyl carbinol derivatives. Successful removal of the directing groups without affecting the reactive penta-1,2,4-triene substructure of the products is demonstrated.
由于累积双键的竞争性固有反应性,选择性过渡金属介导的丙二烯 C(sp)-H 键的活化是一个巨大的挑战。在此,我们报告了一种 Pd 催化的电子非均匀丙二烯的 C-H 烯基化反应,以高达 94%的收率得到了五-1,2,4-三烯产物。一个吡啶甲酰胺导向基团能够形成假定的烯丙基钯配合物,它随后与缺电子的烯烃偶联试剂进行周转限制的 Heck 型反应。该机理假设与实验和计算研究一致。此外,我们首次报道了使用吡啶甲酰胺缩醛作为 C-H 活化反应的易去除助剂,允许烯丙基甲醇衍生物的有效烯基化。成功地去除导向基团而不影响产物的反应性五-1,2,4-三烯结构得到了证明。