Chemoselective or Regioselective?

Over the past two decades, there has been a notable increase in the number of reactions that have been classified as chemoselective and/or regioselective. It is somewhat surprising that neither of these terms is clearly defined, as this often leads to conflicting and confusing designations and makes it challenging to report the results coherently. This perspective presents a brief overview of the origin and evolution of both of these appellations, with specific examples illustrating the problems arising from the current definitions recommended by IUPAC in 2021. It also proposes definitions for the terms chemoselectivity and regioselectivity that will allow an unambiguous description of the observed reaction selectivity. The proposed refinement of nomenclature is exemplified by a variety of chemical transformations.