Novel Reagents for Carbon-Atom and CNN/CCO-Transfer

Reactive intermediates are often considered too short-lived to be studied directly, yet their controlled stabilization offers unique opportunities to uncover new reactivity and develop novel synthetic methods. This lecture will demonstrate how the investigation of reactive intermediates has led to the development of new fragment transfer reagents. A central focus will be on diazoalkenes (R₂C=C=N₂), elusive intermediates long proposed in important reactions such as the Seyferth–Gilbert homologation but historically only observed under matrix-isolation conditions. We show that diazoalkenes can be rationally designed to be room-temperature stable compounds, enabling their direct characterization and systematic study. These stable diazoalkenes exhibit unusual reactivity, including N₂/CO exchange and the generation of triplet vinylidenes, and serve as versatile platforms for reagent development Building on these findings, we have developed new fragment transfer reagents that enable the controlled direct installation of single C-atoms as well as CN₂ and CCO units. Their reactivity and applications in synthesis will be discussed.