Asymmetric cycloaddition reactions catalyzed by bifunctional thiourea and squaramide organocatalysts: recent advances

High on the list of challenges in organic chemistry is the development of new efficient chiral catalysts for enantioselective cycloaddition reactions, which are among the most useful processes in chemical synthesis. In the past few decades, various highly enantioselective bifunctional organocatalysts for different versatile cycloaddition reactions have been developed. In most cases, these organocatalytic cycloadditions (e.g. [4 + 2], [3 + 2], formal [3 + 2], formal [3 + 3], formal [5 + 1], [5 + 2], 1,3-dipolar cycloadditions and Tamura cycloaddition) provide the most convenient and economical routes to nitrogen- and oxygen-containing heterocyclic bioactive molecules. This minireview summarizes the recent developments in this field using chiral bifunctional amine-thiourea and amine-squaramide organocatalysts.