Squaramide Explained

Squaramide is the organic compound with the formula O2C4(NH2)2. Not an amide in the usual sense, it is a derivative of squaric acid wherein the two OH groups are replaced by NH2 groups. Squaramides refer to a large class of derivatives wherein some of the H's are replaced by organic substituents. Exploiting their rigid planar structures, these compounds are of interest as hydrogen-bond donors in supramolecular chemistry and squaramide catalysis.[1] Squaramides exhibit 10-50x greater affinity for halides than do thioureas. Squaramides also find application in medicinal chemistry, metabolomics and material science due to their ability to selectively conjugate amines[2] [3]

Squaramide is prepared by ammonolysis of diesters of squaric acid:[4] [5]

O2C4(OEt)2 + 2 NH3 → O2C4(NH2)2 + 2 EtOHN-Substituted squaramides are prepared similarly, using amines in place of ammonia.

References

  1. Chauhan, P. . Mahajan, S. . Kaya, U. . Hack, D. . Enders, D. . Bifunctional Amine-Squaramides: Powerful Hydrogen-Bonding Organocatalysts for Asymmetric Domino/Cascade Reactions. Adv. Synth. Catal.. 2015. 357. 2–3. 253–281. 10.1002/adsc.201401003.
  2. Lin . Weifeng . Yang . Zhen . Kaur . Amanpreet . Block . Annika . Vujasinovic . Miroslav . Löhr . J.-Matthias . Globisch . Daniel . 2021 . Squaric acid as a new chemoselective moiety for mass spectrometry-based metabolomics analysis of amines . RSC Chemical Biology . en . 2 . 5 . 1479–1483 . 10.1039/D1CB00132A . 2633-0679 . 8496035 . 34704052.
  3. Wurm . Frederik R. . Klok . Harm-Anton . 2013 . Be squared: expanding the horizon of squaric acid-mediated conjugations . Chemical Society Reviews . en . 42 . 21 . 8220–8236 . 10.1039/c3cs60153f . 23873344 . 0306-0012.
  4. Encyclopedia: Squaramide. Storer, R. Ian. e-EROS Encyclopedia of Reagents for Organic Synthesis. 2013. 10.1002/047084289X.rn01531 . 978-0-471-93623-7.
  5. 10.1039/c0cs00200c. Squaramides: Physical properties, synthesis and applications. 2011. Ian Storer. R.. Aciro. Caroline. Jones. Lyn H.. Chemical Society Reviews. 40. 5. 2330–2346. 21399835.

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