Preparation 2-Substituted-4-pyridylzinc Bromides via Direct Insertion of Active Zinc and Their Coupling Reactions

摘要

Heterocyclic compounds which contain a pyridine moiety have played a very significant role in a wide range of organic compounds, such as pharmaceuticals, agrochemicals, medicinal chemistry, and material chemistry. For example, bi-pyridine groups were found to be a key element in antibiotics, and pyridylpyrimidines were used as fungicides as well as tyrosine kinase inhibitors. In addition, pyridine-containing oligomers are frequently found in liquid crystals. More specific examples utilizing 4-pyridyl moiety are also found in a wide spread of fields in chemistry. Consequently, new practical synthetic approaches for introducing a pyridine ring into complex organic molecules are of high value. To this end, transition-metal-catalyzed cross-coupling reactions of pyridylmetallic reagents have been frequently utilized. However, the preparation of electron-deficient pyridyl organo-metallic reagents has been a challenging subject mainly because of some difficulties such as instability and formation of by-products. In addition to those difficulties, the regio-chemistry should be considered when the corresponding pyridylmetallic reagents were prepared because, unlike benzene, pyridine ring has unevenly distributed electrons.