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Synthesis 1980; 1980(12): 961-994
DOI: 10.1055/s-1980-29291
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Reaktionen von Quadratsäure und Quadratsäure-Derivaten

Arthur H. Schmidt*
  • *Abteilung für Organische Chemie und Biochemie der Fachhochschule Fresenius, Kapellenstraße 11-15, D-6200 Wiesbaden
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Publication Date:
24 February 2006 (online)

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A survey of the reactivity of squaric acid and its derivatives is given. The chemical properties of squaric acid are mainly determined by its acidic character and its reactivity is comparable to that of dicarboxylic acids. One of the principal reaction types of squaric acid is its derivatization, i.e., the replacement of one or two OH groups by other hetero groups to give "vinylogous dicarboxylic acid derivatives" such as squaric acid dichloride, esters, amides, etc. A special reaction type found with squaric acid and some of its derivatives is the formation of 1,3-disubstituted squaric acid derivatives containing delocalized bonds ("squaraines") via condensation or isomerization reactions. 1. Squaric Acid and Simple Derivatives 1.1. Squaric Acid 1.2. Squaric Acid Salts (Squarates) 1.3. Simple Squaric Acid Derivatives 1.4. Physical Properties 2. Exchange of Monovalent Groups in Squaric Acid and 1,2-Disubstituted Squaric Acid Derivatives 2.1. Reaction with Alcohols 2.2. Reaction with Thiols, Hydrogen Sulfide, and Hydrogen Selenide 2.3. Reaction with Monoamines 2.4. Reaction with Diamines 2.5. Reaction with Hydrazines 2.6. Reaction with Phosphines 2.7. Reaction with Organometallic Compounds and with Carbanions 2.8. Reaction with Electron-rich Alkenes 2.9. Reaction with Arenes 3. Exchange of Bivalent Groups in 1,2-Disubstituted Squaric Acid Derivatives 4. 1,3-Disubstituted Squaric Acid Derivatives (Squaraines) 4.1. Diaminosquaraines from Squaric Acid and Primary or Secondary Amines 4.2. Diaminosquaraines by Isomerization of Squaric Acid 1,2-Diamines 4.3. Diaminosquaraines from Dialkoxycyclobutenediones and Primary or Secondary Amines 4.4. Transamidation of Diaminosquaraines 4.5. Squaraines from Squaric Acid and Pyrroles or Indoles 4.6. Squaraines from Squaric Acid and Tertiary Amines 4.7. Squaraines from Dialkoxycyclobutenediones and Pyrroles or Indoles 4.8. Squaraines from Dipyrrolylsquaraines by Pyrrolyl-Group Exchange 4.9. Miscellaneous 1,3-Disubstituted Squaric Acid Derivatives 4.10. Thiosquaraines 5. Miscellaneous Reactions of Squaric Acid and its Derivatives 5.1. Protonization 5.2. Oxidation 5.3. Ring Contraction 5.4. Ring Enlargement 5.5. Ring Cleavage

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