Advances in Bifunctional Squaramide-Catalyzed Asymmetric Sulfa-Michael Addition: A Decade Update

The application of bifunctional organocatalysts in organic chemistry has advanced remarkably owing to their high stability to moisture and air, relatively low toxicity, ease of handling, and recoverability. Among chiral bifunctional organocatalysts, squaramides have emerged as a privileged catalyst in recent years. This review article presents a comprehensive report on fine-tunable bifunctional chiral squaramide-catalyzed sulfa-Michael addition, which is based upon synchronous interplay of synergistic 'electrophilic-nucleophilic' dual activation strategies via multiple H-bonding interactions for the construction of both common and complex molecular entities bearing multiple stereocenters. Mechanistic discussions are kept brief, but significant understandings have been recorded. The contribution of squaramide catalyst to the construction of C-S bonds via sulfa-Michael addition has been applied in medicinal, natural, and industrial chemistry. Attention is focused on summarizing the progress made in chiral squaramide-catalyzed asymmetric sulfa-Michael addition and subsequent cascade/domino reaction sequences between 2011 and 2022. 1 Introduction 2 Quinine-Squaramide Organocatalysis 3 Iminophosphorane-Squaramide Organocatalysis 4 Chinchona-Squaramide Organocatalysis 5 trans-1,2-Diaminocyclohexane-Squaramide Organocatalysis 6 Conclusion