Department of Chemistry and Biochemistry, North Dakota State University, Fargo, ND 58108⁻6050, USA.
Molecules. 2019 Jan 9;24(2):215. doi: 10.3390/molecules24020215.
Over the past few decades, transition metal catalysis has witnessed a rapid and extensive development. The discovery and development of cross-coupling reactions is considered to be one of the most important advancements in the field of organic synthesis. The design and synthesis of well-defined and bench-stable transition metal pre-catalysts provide a significant improvement over the current catalytic systems in cross-coupling reactions, avoiding excess use of expensive ligands and harsh conditions for the synthesis of pharmaceuticals, agrochemicals and materials. Among various well-defined pre-catalysts, the use of Pd(II)-NHC, particularly, provided new avenues to expand the scope of cross-coupling reactions incorporating unreactive electrophiles, such as amides and esters. The strong σ-donation and tunable steric bulk of NHC ligands in Pd-NHC complexes facilitate oxidative addition and reductive elimination steps enabling the cross-coupling of broad range of amides and esters using facile conditions contrary to the arduous conditions employed under traditional catalytic conditions. Owing to the favorable catalytic activity of Pd-NHC catalysts, a tremendous progress was made in their utilization for cross-coupling reactions via selective acyl C⁻X (X=N, O) bond cleavage. This review highlights the recent advances made in the utilization of well-defined pre-catalysts for C⁻C and C⁻N bond forming reactions via selective amide and ester bond cleavage.
在过去的几十年中，过渡金属催化已经取得了快速而广泛的发展。交叉偶联反应的发现和发展被认为是有机合成领域最重要的进展之一。设计和合成结构明确且在实验台上稳定的过渡金属预催化剂，相对于当前的交叉偶联反应催化体系有了显著的改进，避免了昂贵配体的过度使用和对药物、农用化学品和材料合成的苛刻条件。在各种结构明确的预催化剂中，Pd(II)-NHC 的使用为扩展包括酰胺和酯在内的惰性亲电试剂的交叉偶联反应范围提供了新途径。Pd-NHC 配合物中 NHC 配体的强 σ-给电子和可调的空间位阻促进了氧化加成和还原消除步骤，使得在温和条件下可以实现广泛的酰胺和酯的交叉偶联，而在传统催化条件下则需要苛刻的条件。由于 Pd-NHC 催化剂具有良好的催化活性，因此在通过选择性酰基 C⁻X（X=N、O）键断裂进行交叉偶联反应中的应用取得了巨大进展。本文综述了最近在通过选择性酰胺和酯键断裂形成 C⁻C 和 C⁻N 键的反应中，使用结构明确的预催化剂方面的进展。
