Vitamin B12 plays a key role in many metabolic processes occurring in all mammals. Over the years its biological role has been extensively studied generating a lot of interest in the chemistry of this vital molecule. This established a variety of new methodologies for the synthesis and analysis of new cobalamin derivatives as well as creative purification techniques. This tutorial review summarizes all the advancements made in this area, providing a deeper insight into vitamin B12 chemistry.

Cobalester, a natural nontoxic vitamin B12 derivative, was found to catalyse unusual olefinic sp(2) C-H alkylation with diazo reagents as a carbene source instead of the expected cyclopropanation.