Chromones Pechmann coumarin synthesis

The vigorous conditions which are necessary serve to detract from the value of the Perkin synthesis, leading to the production of tarry material which adversely affects the yield of coumarin. Difficulties encountered in the synthesis of substituted o-hydroxybenzaldehydes also limit the application of this route. The obvious advantages of the method are that there are no doubts about the orientation of the product and that, unlike the Pechmann reaction, formation of the isomeric chromones is not possible. 

The Simonis chromone synthesis is the reaction of a phenol la-c with a P-keto ester 2 using an appropriate acid promoter to generate a chromone or benzo-y-pyrone 3 (also called a benzo-l,4-pyrone). While compound 3 is actually a chromenone, for this article, whether the double bond is present or not, the system will be characterized as a chromone. The condensation is related to the Pechmann-Duisberg reaction, which yields coumarins from the condensation of a phenol with a P-keto ester and like its relative, the reaction conditions require the loss of water from the ketone moiety and alcohol from the ester moiety. 

Simonis continued to prove the correct structural assignment by degradation and began exploring the scope and limitation of the reaction As more co-workers joined in the exploration, many were convinced that Simonis did not make the chromone, but actually made the coumarin and that the structure was merely misassigned. While descriptions of early work solely on the Simonis chromone synthesis are lacking, reviews on the synthesis of coumarins (the Pechmann reaction) typically include an overview on the Simonis chromone synthesis " ... 

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