The role of 1,4-palladium migration in C(sp3)–H functionalization

Abstract

The design of methods for C(sp³)–H functionalization of organic compounds is significantly vital for researchers, as they can facilitate the synthesis of various compounds essential for future applications, including natural products and pharmaceuticals. This advancement provides vital tools for creating diverse organic compounds necessary for innovation in drug design and development. Palladium is considered the most effective and commonly employed transition metal in the construction of organic compounds. In recent years, it has demonstrated the ability to catalyze a variety of C–H activation approaches. Palladium-catalyzed C–H activation methods provide notable benefits compared to those facilitated by other metals, as the formed C–palladium bond can take part in numerous follow-up transformations, leading to a broad variety of products. This versatility maximizes the utility and diversity of C–H functionalization processes. One strategy that aids in the functionalization of C(sp³)–H bonds is the 1,4-palladium migration. Furthermore, the most frequently observed palladium migration is the 1,4-migration. In this type of migration, the palladium moves from one carbon atom to another carbon atom that is separated by two intervening atoms. This process tends to be favored because it can lead to the formation of a relatively strain-free five-membered palladacycle and is also promoted by the palladium's close proximity to the C–H bond. This type of migration plays a crucial role in the functionalization of C(sp³)–H bonds, particularly in molecules equipped with traceless directing groups. In this review, the focus is on the impact of 1,4-palladium migration in C(sp³)–H functionalization and how this process selectively activates specific hydrogen atoms within organic compounds.