Chemical biology develops molecular tools for studying biological processes, setting the basis for new diagnostics and therapeutics, and relies heavily on the ability to modify selectively biomolecules. In our work, we introduce hypervalent iodine bonds into peptides and proteins, via functionalization of cysteine, by using unique cyclic reagents developed in our group. The hypervalent bond can then be selectively modified in the presence of both natural and synthetic functional groups, opening new opportunities for applications in chemical biology.

Azides are building blocks of increasing importance in synthetic chemistry, chemical biology, and materials science. Azidobenziodoxolone (ABX, Zhdankin reagent) is a valuable azide source, but its safety profile has not been thoroughly established. Herein, we report a safety study of ABX, which shows its hazardous nature. We introduce two derivatives, tBu-ABX and ABZ (azidobenziodazolone), with a better safety profile, and use them in established photoredox- and metal-mediated azidations, and in a new ring-expansion of silylated cyclobutanols to give azidated cyclopentanones.

A methodology for the C−H azidation of N‐terminal proline‐containing peptides was developed employing only commercially available reagents. Peptides bearing a broad range of functionalities and containing up to 6 amino acids were selectively azidated at the carbamate‐protected N‐terminal residue in presence of the numerous other functional groups present on the molecules. Post‐functionalizations of the obtained aminal compounds were achieved: cycloaddition reactions or C−C bond formations via a sequence of imine formation/nucleophilic addition were performed, offering an easy access to diversified peptides.

In this short review, we describe applications of hypervalent iodine reagents for the azidation of organic compounds from the seminal publications to the most recent reports. After reviewing selected examples of azidations based on the use of in situ formed unstable non-cyclic reagents, we focus more in details on stable cyclic hypervalent iodine reagents. Important advances in the azidation of C–H bonds, alkenes as well as other transformations are described. Rather than being comprehensive, we selected to highlight the key reports that especially contributed to the advancement of research in the field in our opinion. Table of content: 1. Introduction 2. Non-Cyclic λ3-Iodanes 3. Heterocyclic λ3-Iodanes 3.1 Azidation of aliphatic C–H Bonds 3.2 Azidation of Alkenes 3.3 Other Azidations 4. Conclusion and Outlook

The first examples of direct synthesis of γ-thiolactones by addition of a thiolactone-based radical are described. Mono- and bis-γ-thiolactones can be obtained by a dilauroyl peroxide initiated addition of thiolactone xanthate to various alkenes and α,ω-dienes. The process is modular and exhibits a high functional group tolerance.