The first Suzuki cross-couplings of unactivated tertiary alkyl electrophiles are described. The method employs a readily accessible catalyst (NiBr2 center dot diglyme/4,4'-di-tert-butyl-2,2'-bipyridine, both commercially available) and represents the initial example of the use of a group 10 catalyst to cross-couple unactivated tertiary electrophiles to form C-C bonds. This approach to the synthesis of all-carbon quaternary carbon centers does not suffer from isomerization of the, alkyl group, in contrast with the umpolung strategy for this bond construction (cross-coupling of a tertiary alkylmetal with an aryl electrophile). Preliminary mechanistic studies are consistent with the generation of a radical intermediate along the reaction pathway.
Silicon–Carbon Bond Formation via Nickel-Catalyzed Cross-Coupling of Silicon Nucleophiles with Unactivated Secondary and Tertiary Alkyl Electrophiles
作者:Crystal K. Chu、Yufan Liang、Gregory C. Fu
DOI:10.1021/jacs.6b03465
日期:2016.5.25
cross-coupling methods for the formation of C-C bonds from unactivated alkyl electrophiles have been described in recent years. In contrast, progress in the development of methods for the construction of C-heteroatom bonds has lagged; for example, there have been no reports of metal-catalyzed cross-couplings of unactivated secondary or tertiaryalkyl halides with silicon nucleophiles to form C-Si bonds. In this
近年来,已经描述了用于从未活化的烷基亲电试剂形成 CC 键的一系列交叉偶联方法。相比之下,C-杂原子键构建方法的开发进展滞后;例如,没有关于未活化的仲或叔烷基卤化物与硅亲核试剂在金属催化下交叉偶联形成 C-Si 键的报道。在这项研究中,我们解决了这一挑战,确定了一种简单的市售镍催化剂(NiBr2·二甘醇二甲醚)可以在异常温和的条件下(例如,-20°C)实现烷基溴与亲核硅试剂的偶联;特别值得注意的是我们能够使用未活化的叔烷基卤化物作为亲电偶联伙伴,这在交叉偶联化学领域还比较少见。立体化学、相对反应性和自由基陷阱研究与 CX 键裂解的均裂途径一致。