Abstract:
Chiral analogues of squaramides have been fruitful
in organocatalyzed asymmetric reactions over last decade.
Alongside other H-bonding catalysts like ureas, thioureas:
squaramides have been proved to be efficient asymmetric
catalysts for the formation of acyclic and cyclic chiral
molecules. A wide range of cyclic molecules bearing multiple
functionalities and stereocenters have been synthesized by
using several bifunctional squaramides as catalysts. These
catalysts perform as base utilizing basic N atom in their chiral
extension and help in stereoinduction by forming H-bonds
with suitable H-bond acceptors. The present review focuses
on assembling recent progresses of asymmetric synthesis of
five and six membered rings promoted by squaramides. A
handful of articles have been published by several research
groups documenting asymmetric construction of five- and
six-membered rings as part of interesting and complex
molecular architectures. Different methodologies like conventional and formal cycloadditions or cascade reactions have
been engineered through the assistance of chiral squaramides to fabricate the carbo- and heterocycles. This review
also includes dual and cooperative catalytic system in which
squaramide is one of the catalysts.
