Selective N ‐Functionalization of Pyrazoles

Pyrazoles are five‐membered heteroarenes that contain two neighboring nitrogen atoms and appear in diverse functional molecule classes. One nitrogen contributes a lone‐pair to the aromatic π‐system, while the lone‐pair of the other lies orthogonal. However, easy interconversion between tautomers of N─H pyrazoles occurs and the two forms lie close in energy to each other. As a consequence, N ‐functionalization reactions most commonly lead to mixtures of products in what is a well‐known synthetic challenge. Demand for selective, efficient alternatives has prompted innovation of new, diverse synthetic strategies which can overcome this problem. In this review, we focus on the most recent developments in this field.