ThePechmann Reaction

Abstract

H. v. Pechman found that coumarin derivatives are formed when malic acid or beta‐ketonic esters are condensed with phenols in the presence of concentrated sulfuric acid. This reaction is commonly known s the Pechmann reaction. It has found extensive use. Simonis and co‐workers used phosphorus pentaoxide as the condensing agent in place of sulfuric acid and demonstrated that with the same reactants chromones rather than coumarins resulted. The condensation of a phenol and beta‐ketonic ester in the presence of phosphorus pentaoxide is sometimes called the Simonis reaction, but it is actually a variation of the Pechmann reaction and is considered in this chapter. Other condensing agents that have been used, for example, are phosphorus oxychloride, phosphoric acid, zinc chloride and others. These are discussed in the chapter. By condensing appropriately substituted phenols and beta‐ketonic esters, coumarins can be synthesized with substituents either in the benzene nucleus in the heterocyclic ring or both. The course of this reaction depends on three factors; nature of the phenol, of the beta‐ketonic ester, and the condensing agent.

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“…2a, he made a coumarin by treating the sodium salt of ortho-hydroxybenzaldehyde (also known as salicylic aldehyde) with acetic anhydride [6][7][8]. Since the report of famous coumarin synthesis, many other novel methods have been developed by Pechmann [9][10][11], Claisen [12], Knoevenagel [13,14], Reformatsky [15], and Wittig [16] for the synthesis of pyrone-ring moieties in coumarins. Among them, Pechmann reaction has been widely used for the preparation of coumarins, especially for 4-substituted coumarins, since it proceeds from very simple starting materials, such as phenols and b-ketoesters or a,b-unsaturated carboxylic acids in the presence of acid catalysts (see Fig.…”

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Silica supported boric tri-sulfuric anhydride as a novel and efficient catalyst for solvent-free synthesis of coumarins via Pechmann condensation

“…Among the methods applied, Pechmann reaction is the most widely applied method for synthesizing coumarins as it involves the condensation of phenols with β-ketoesters in the presence of a variety of acid condensing agents and gives good yields of 4-substituted coumarins. 12 Several acid catalysts have been used in the Pechmann reaction including Lewis, 13 protic 14 and solid acids. 15 The Pechmann reaction has also been carried out using microwave irradiation, 16,17 sonication 18 and in ionic liquids 19 as alternative to conventional methods.…”