Pechmann condensation

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Named reaction for synthesis of coumarins

title: "Pechmann condensation" type: doc version: 1 created: 2026-02-28 author: "Wikipedia contributors" status: active scope: public tags: ["oxygen-heterocycle-forming-reactions", "condensation-reactions", "name-reactions"] description: "Named reaction for synthesis of coumarins" topic_path: "general/oxygen-heterocycle-forming-reactions" source: "https://en.wikipedia.org/wiki/Pechmann_condensation" license: "CC BY-SA 4.0" wikipedia_page_id: 0 wikipedia_revision_id: 0

::summary Named reaction for synthesis of coumarins ::

| Name = Pechmann condensation | Type = Ring forming reaction | NamedAfter = Hans von Pechmann | Section3 = {{Reactionbox Identifiers | OrganicChemistryNamed = pechmann-condensation |Reaction={{Reactionbox Reaction | Reactant1 = Phenol | Reactant2 = β-keto carboxylic acid or β-keto ester | Reagent1= | Product1 =Coumarin(s) | Sideproduct1 = | Reference = | Solvent = | Catalyst = | Temperature = The Pechmann condensation is a synthesis of coumarins, starting from a phenol and a carboxylic acid or ester containing a β-carbonyl group. The condensation is performed under acidic conditions. The mechanism involves an esterification/transesterification followed by attack of the activated carbonyl ortho to the oxygen to generate the new ring. The final step is a dehydration, as seen following an aldol condensation. It was discovered by the German chemist Hans von Pechmann{{cite journal | author= H. v. Pechmann | title = Neue Bildungsweise der Cumarine. Synthese des Daphnetins | journal = Berichte der deutschen chemischen Gesellschaft | year = 1884 | volume = 17 | issue = 1 | pages = 929–936 | doi = 10.1002/cber.188401701248| url = https://zenodo.org/record/1425329 . ::figure[src="https://upload.wikimedia.org/wikipedia/commons/e/e7/Pechmann_Reaction_equation.svg"] ::

Mechanism

To synthesize coumarin derivatives, β-ketoesters can be condensed with phenols under acidic conditions. In this case, a transesterification reaction occurs first with the formation of the phenol ester. This is then followed by ring closure, similar to Friedel-Crafts alkylation.

::figure[src="https://upload.wikimedia.org/wikipedia/commons/c/c0/Pechmann_Reaktionsmechanismus_1.svg" caption="Pechmann Reaktionsmechanismus 1"] ::

Examples

With simple phenols, the conditions are harsh, although yields may still be good.

::figure[src="https://upload.wikimedia.org/wikipedia/commons/8/85/Pechmann_4methyllcoumarin.png" alt="The Pechmann condensation as applied to 4-methylcoumarin"] ::

With highly activated phenols such as resorcinol, the reaction can be performed under much milder conditions. This provides a useful route to umbelliferone derivatives:

::figure[src="https://upload.wikimedia.org/wikipedia/commons/d/d3/Pechmann_4methylumbelliferone.png" caption="The Pechmann condensation as applied to 7-hydroxy-4-methylcoumarin"] ::

For coumarins unsubstituted at the 4-position, the method requires the use of formylacetic acid or ester. These are unstable and not commercially available, but the acid may be produced in situ from malic acid and sulfuric acid above 100 °C. As soon as it forms, the formylacetic acid performs the Pechmann condensation. In the example shown, umbelliferone itself is produced, albeit in low yield:

::figure[src="https://upload.wikimedia.org/wikipedia/commons/e/e0/Pechmann_umbelliferone.png" caption="The Pechmann condensation as applied to umbelliferone"] ::

Mechanistic studies

The mechanism of the reaction has been studied in details with theoretical treatment.

The study shown that reaction takes place on oxo-form, and not on enolic-form. Three different oxo-routes have been proposed.

Simonis chromone cyclization

In a variation the reaction of phenols and beta-ketoesters and phosphorus pentoxide yields a chromone. This reaction is called Simonis chromone cyclization. The ketone in the ketoester is activated by P2O5 for reaction with the phenol hydroxyl group first, the ester group in it is then activated for electrophilic attack of the arene.

::figure[src="https://upload.wikimedia.org/wikipedia/commons/6/69/Simonis_Chromone_Cyclisation.svg"] ::

References

References

  1. J. A. Joule, K. Mills ''Heterocyclic Chemistry'', 4th edition, Blackwell Science, Oxford, UK, 2000.
  2. J. A. Joule, K. Mills ''Heterocyclic Chemistry'', 4th edition, Blackwell Science, Oxford, UK, 2000.
  3. link. (2011-05-14 .)
  4. Daru, János. (4 November 2011). "Mechanism of the Pechmann Reaction: A Theoretical Study". The Journal of Organic Chemistry.
  5. E. Petschek, H. Simonis, Ber. 46, 2014 (1913).
  6. ''Name reactions: a collection of detailed reaction mechanisms'', Jie Jack Li.

::callout[type=info title="Wikipedia Source"] This article was imported from Wikipedia and is available under the Creative Commons Attribution-ShareAlike 4.0 License. Content has been adapted to SurfDoc format. Original contributors can be found on the article history page. ::

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