Abstract
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
Key words
organocatalyst - sulfa-Michael addition - bifunctional chiral squaramide - H-bonding
- stereoselectivity