Recent Advances in the Chemistry of 5 and 6‐Membered Selenacycles and Selenaheterocycles

In recent years, selenium and selenium-containing compounds have attracted increasing attention due to their fascinating biological activities and synthetic versatility. This review aims to highlight the recent advances in the chemistry of cyclic structures incorporating this valuable yet rare heteroatom. Special emphasis is given to 5- and 6-membered rings containing selenium, including combinations with other heteroatoms such as oxygen and nitrogen. To provide a comprehensive and up-to-date overview, we have summarized contributions reported between 2020 and 2024, addressing both synthetic methods and medicinal chemistry aspects where relevant. Following an introductory section, the review explores the chemistry of 5-membered rings, including selenophenes, benzo(heteroaryl)selenophenes, and tetrahydroselenophenes. Subgroups such as 1,3-selenazoles and 1,3-oxaselenolanes are discussed in detail, alongside a dedicated analysis of benzisoselenazolones. Among these, ebselen—a prototypical benzisoselenazolone and one of the most extensively studied selenium-based compounds—is given particular attention. The discussion then shifts to 6-membered rings, encompassing among others selenomorpholines, 1,3-selenazinanes, 1,2,4-selenadiazinanes, and tetrahydro-2H-selenopyranes, with a focus on their unique chemical properties and potential applications. The review concludes with a summary and an outlook on future research directions in this evolving field.