Vitamin B₁₂ (cobalamin, 1) is one of a few naturally occurring organometallic molecules. As a cofactor for adenosylcobalamin-dependent and methylcobalamin-dependent enzymes, it plays a crucial role in biological processes, including DNA synthesis and regulation, nervous system function, red blood cell formation, etc. Enzymatic reactions, such as isomerisation, dehalogenation, and methyl transfer, rely on the formation and cleavage of the Co–C bond. Because it is a natural, nontoxic, environmentally benign cobalt complex, cobalamin (1) has been successfully utilised in organic synthesis as a catalyst for Co-mediated reactions. This tutorial review concisely describes cobalamin-catalysed organic reactions that hold promise for environmentally friendly cobalt catalysis, leaving the reader with basic knowledge and the ability to harness the catalytic potential of this fascinating molecule.

Chemistry of diazo compounds is dominated by transition metal catalysis but recently, photoinitiated reactions of diazo compounds have attracted a lot of attention. This mini-review describes recent discoveries on the reactivity of diazo compounds under light irradiation.

This Feature Article provides an overview of research advances in the chemistry of spring-loaded molecules, focusing mainly on strain-release transformations.

The development of new sustainable reactions and protocols is essential to fulfill the growing demands of every branch of organic chemistry for greener synthetic methodologies. In this context, the use of visible light as the only source of energy is highly appealing. Since diazo compounds are valuable reagents in organic synthesis, their transformations realized in a sustainable manner are of interest. High reactivity and easy availability make them suitable for solar-driven transformations. Indeed, photochemical reactions of diazo compounds have recently proven a valuable alternative to transition metal catalysis. In this perspective, we highlight applications of these reagents under visible irradiation, particularly focusing on recent advancements. These include photochemical generation of carbenes and radicals which involve many relevant reactions, [2+1]-cycloadditions, X–H and C–H insertions, Wolff rearrangement, and more. Mechanistic aspects of these processes are briefly addressed to give readers a deeper understanding of rules underlying photoreactivity of diazo compounds. We conclude by emphasizing significant advancements and discussing challenges for future developments in the photochemistry of these valuable reagents.