两个结构相似的卤代烷烃直接经过镍催化还原偶联反应生成新的 C(sp3 )—C(sp3 ) 键 一直是有机合成中的难点. 通过前期的研究发现, 采用 Zn 作还原剂, Ni(cod)2 作催化剂, 在 Pybox 类配体存在的条件下, 可以成功地实现不同卤代烷烃的交联反应, 不过其中一个卤代烷烃必须使用 3 mol 的用量. 为了进一步提高反应的效率, 采用 2 mol 的 1-溴丁烷和 1 mol 的 4-溴-1-对甲苯磺酰基哌啶为模型进行反应, 通过优化反应条件, 特别是对配体结构的修饰, 进一步提高不活泼烷基卤代物的还原交叉偶联反应效率. 研究结果表明, Pybox 类配体是效果较好的配体, 而二齿配体在吡啶存在的条件下也能得到中等期望值的产率. 这一结果为今后进一步优化反应提供了参考依据.
Construction of C(sp3)—C(sp3) bonds through direct nickel-catalyzed reductive cross-coupling of two structurally similar alkyl halides remains a challenge in organic synthesis. In the previous studies, under catalytic Ni(cod)2 in the presence of stoichiometric amount of Zn as reductant, two different alkyl halides can efficiently undergo coupling to give desired alkyl-alkyl products. However, one of the reactants has to be largely excessive. In order to improve coupling efficiency, this reaction by using 1 mol of (4-CI)-H-Pybox and 2 mol of Ni(cod)2 as model reactants was optimized. After screening a variety of tridentate and bidentate ligands, it was determined that the ligand remained optimal. However, bidentate ligand also gave moderate results in the presence of pyridine. This result may become important in future optimization.
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