Improved Synthesis of 6-Chloro-5-methylpyridin-2-amine: A Key Intermediate for Making Lumacaftor

Pd-Catalyzed C(sp2)-C(sp3) Suzuki Coupling and Synthesis of Lumacaftor Using Designed Monophosphine Ligands

Novel monophosphine ligands L1 and L2 with a C-P ring were designed and synthesized for the efficient Pd-catalyzed C(sp2)-C(sp3) Suzuki coupling. With 0.5 mol % Pd2dba3 and 2 mol % L1, aryl halides coupled with alkylboronic acids to give the products in up to 99% yield. The aryl thianthrene salt was further applied for late-stage methylation in 97% yield. The active pharmaceutical ingredient lumacaftor was synthesized by aryl-alkyl and aryl-aryl Suzuki coupling reactions using L1 and L2.

Palladium-Catalyzed Carbonylation of Aryl Bromides with Carbon Dioxide To Access Aryl Carboxylic Acids under Mild Conditions

A palladium-catalyzed direct carbonylation of aryl bromides with carbon dioxide as the carbonyl source has been developed by using Pd(dba)₂/DPEPhos as the catalyst under mild reaction conditions, providing an efficient route to a variety of aryl carboxylic acids in moderate to high yields. The methods have many advantages such as the use of a simple palladium catalyst system, wide substrate scope, good functional group tolerance, high yields, and easy scalability.

Recent Applications of Pd-Catalyzed Suzuki–Miyaura and Buchwald–Hartwig Couplings in Pharmaceutical Process Chemistry

Cross-coupling reactions have changed the way complex molecules are synthesized. In particular, Suzuki–Miyaura and Buchwald–Hartwig amination reactions have given opportunities to elegantly make pharmaceutical ingredients. Indeed, these reactions are at the forefront of both the stages of drug development, medicinal chemistry, and process chemistry. On the one hand, these reactions have given medicinal chemists a resource to derivatize the core compound to arrive at scaffold rapidly. On the other hand, these cross couplings have offered the process chemists a smart tool to synthesize the development candidates safely, quickly, and efficiently. Generally, the application of cross-coupling reactions is broad. This review will specifically focus on their real (pharma) world applications in large-scale synthesis appearing in the last three years.

Directing Group Enables Electrochemical Selectively Meta-Bromination of Pyridines under Mild Conditions

Without the use of catalysts and oxidants, a facile and sustainable electrochemical bromination protocol was developed. By introducing the directing groups, the regioselectivity of pyridine derivatives could be controlled at the meta-position utilizing the inexpensive and safe bromine salts at room temperature. A variety of brominated pyridine derivatives were obtained in 28-95% yields, and the reaction could be readily performed at a gram scale. By combining the installation and removing the directing group, the concept of meta-bromination of pyridines could be verified.

Access to 2-pyridinylamide and imidazopyridine from 2-fluoropyridine and amidine hydrochloride

Under catalyst-free conditions, an efficient method to synthesize 2-pyridinylamides has been developed, and the protocol uses inexpensive and readily available 2-fluoropyridine and amidine derivatives as the starting materials. Simultaneously, the copper-catalysed approach to imidazopyridine derivatives has been established with high chemoselectivity and regiospecificity. The results suggest that the nitrogen-heterocycles containing iodide substituents can also be compatible for the reaction via the cascade Ullmann-type coupling, and the nucleophilic substitution reaction provides the target products in a one-pot manner.