Advances in Zr-mediated radical transformations and applications to total synthesis

Radical reactions, which have been reported in large numbers in recent years, have exerted major influence across fields where organic synthesis plays a central role, including pharmaceuticals, agrochemicals, materials chemistry, organic semiconductors, and organic thin-film solar cells. These areas are intimately linked to human life; thus, advances in organic synthesis are essential for improving human well-being. Nearly two centuries after the seminal 1828 synthesis of urea from inorganic precursors – often regarded as the birth of organic synthesis – the field continues to evolve rapidly and to exert profound impact on society. A retrospective of almost 200 years of organic synthesis shows that the development and discovery of two-electron ionic transformations dominated the early stages. Over time, pericyclic reactions exemplified by the Woodward–Hoffmann rules and one-electron radical processes became prominent research topics. Today, many of these classical transformations have been further refined to afford reactions that are cheaper, safer, and less toxic. In this context, we focus on mild radical reactions mediated by zirconium (Zr), which has recently attracted attention because of its low toxicity and ease of handling. We discuss the utility of Zr in such radical processes and consider prospects for future development.