Introduction
Interest in squaramides has grown drastically over the last few years. One of the
reasons is that squaramides can be used in many different ways in important fields
such as organic chemistry, medicine, and chemical biology.
First of all, the rigidity of their cyclobutadienedione rings, the restricted rotation
around the C–N bonds,[1] and the possibility of having both acidic hydrogens[2] and basic functionalities in a single molecule make them effective bifunctional
organocatalysts for asymmetric reactions.[3]
Furthermore, they act as ion detectors, forming hydrogen bonds with the corresponding
anion or cation.[2b]
[4] The interaction with anions through hydrogen bonding also brought them to the attention
of studies regarding transmembrane anion transport.[5]
In addition, squaramides have shown antimalarial,[6] antibacterial,[7] and anticancer[8] activity.
Preparation
Squaramides are usually synthesized under mild conditions in high yields, and both
symmetric and asymmetric squaramides are accessible (Scheme [1]).[9]
Scheme 1 Synthesis of an asymmetric squaramide by Rawal[10]
