Chromones formation, Simonis reaction

Although there is evidence that chromone syntheses which proceed by the cyclization of phenyl esters under Friedel-Crafts conditions may involve a Fries rearrangement and hence require the formation of one bond adjacent to the heteroatom, syntheses of chromones from phenols will be considered together in this section. The Simonis reaction (530R(7)l)... 

In 1913, Simonis and co-workers first reported the isolation of the 2,3-dimethyl chromone 5 by reaction of phenol la with ethyl 2-methyl-acetylacetate. While the product was reported in poor yield, the reaction was a change from the typically reported formation of the coumarin. Simonis did report using a different promoter (P2O5) instead of the traditionally used H2SO4 for the Pechmann reaction. For some time, the differences in the two reactions were thought to be that simple sulfuric acid gave the coumarin as reported by Pechmann and phosphorous pentoxide gave the chromone as reported by Simonis. 

A more recent report on the use of PPE to promote cyclization of a P-naphthol has appeared. The reagent allowed product formation in excellent yield at room temperature. Such results were a great improvement to the reaction conditions and yield typically obtained in the Simonis chromone synthesis. 2,6-Dihydroxy-naphthol 35 gave chromone 36 in 98% yield. 

The Simonis chromone synthesis has also been applied to phenol-like systems. The reaction of 40b (in equilibrium with 40a) with 6 and P2O5 provided a mixture of the Pechmann and Simonis products 41 and 42 when anhydride 40a,b was substituted (R = Me). When the material was unsubstituted (R = H) only 43 was isolated. The authors suggested that the formation of the 1,4-pyran was followed by rearrangement to the more stable product. While the yields were low, entry was established into these highly oxidized bis-pyranyl systems. 

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