Ring Synthesis of Coumarins

1 From Phenols and 1,3-Keto-Esters The Pechmann Synthesis  

Phenols react with P-keto-esters, including cyclic keto-esters, to give coumarins under acid-catalysed conditions - concentrated sulfuric acid, hydrogen fluoride, a cation exchange resin, indium(III) chloride and sulfamic acid (solvent free) are amongst those that have been used. 

Coumarins can be obtained directly, in a one-pot procedure, from phenols and a propiolate, using palladium or platinum catalysis.  

2 From ortho-Hydroxy-Araldehydes and Anhydrides or Esters 

The simplest synthesis of coumarins is a special case of the Perkin condensation, i.e. the condensation of an aromatic aldehyde with an anhydride. orthoAdyAmxy-trans-cmnaimc acids cannot be intermediates since they do not isomerise under the conditions of the reaction nor can 0-acetylsalicylaldehyde be the immediate precursor of the coumarin, since it is not cyclised by sodium acetate on its own.  

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Ring synthesis of coumarins 9.3.2. / From phenols and 1,3-ketoesters... 

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