Institute of Organic Chemistry, National Academy of Sciences of Ukraine, Academician Kukhar Str. 5, 02660 Kyiv, Ukraine.
University of Bielefeld, Universitätstr. 25, 33615 Bielefeld, Germany.
J Org Chem. 2023 Jun 2;88(11):7233-7244. doi: 10.1021/acs.joc.3c00470. Epub 2023 May 17.
Silylformamidine exists in equilibrium with its carbenic form due to an easy migration of the silyl group. The reaction of with variously substituted fluorobenzenes proceeds as an insertion of the nucleophilic carbene into the most acidic C-H bond upon mixing the reagents and does not require any catalyst. According to DFT calculations, the classical interpretation of the insertion reaction proceeding via a three-membered transition state structure requires high activation energy. Instead, low activation barriers are predicted for a transfer of the most acidic proton in the aromatic substrate to the carbene carbon. As the next step, a barrierless rearrangement of the formed ion pair toward the product completes the process. The reactivity of substituted benzenes in the reaction with silylformamidine can be roughly assessed by calculated p (DMSO) values for the C-H hydrogens. Benzene derivatives having p approx. less than 31 can undergo C-H insertion. The reaction provides aminals as the first products, which can easily be transformed into the corresponding aldehydes via acidic hydrolysis. As silylformamidine is tolerant to many functional groups, the reaction can be applied to numerous benzene derivatives, making it a reliable strategy for application in organic synthesis.
硅基甲脒由于硅烷基的易于迁移而处于其碳烯形式的平衡中。与各种取代的氟苯反应通过混合试剂，亲核碳烯插入最酸性的 C-H 键进行，并且不需要任何催化剂。根据 DFT 计算，经典的插入反应通过三员过渡态结构进行的解释需要高的活化能。相反，对于芳香底物中最酸性质子向碳烯碳原子的转移，预测出低的活化势垒。作为下一步，形成的离子对向产物的无势垒重排完成该过程。取代的苯与硅基甲脒反应的反应性可以通过计算 C-H 氢的 p(DMSO) 值来大致评估。具有 p 约小于 31 的苯衍生物可以进行 C-H 插入。反应提供亚胺作为第一个产物，其可以通过酸性水解容易地转化为相应的醛。由于硅基甲脒对许多官能团具有耐受性，因此该反应可以应用于许多苯衍生物，使其成为在有机合成中应用的可靠策略。
