Geometrical inversion in the acids derived from the coumarins. Part IV. The behaviour of the ethers of the cis and trans acids

The methyl ethers of the cis and trans acids from coumarin, 7-methylcoumarin and 6-nitrocoumarin have been obtained by improved methods and their transformation in neutral, acid and alkaline media studied. It has been found that irrespective of the nature of the medium the trans form is the one favoured, thereby showing that the unusual depletion of the trans hydroxy acids (coumaric acids) in neutral and acid media is due to the ready formation of coumarins from the corresponding cis acids, which may exist in small proportions in equilibrium with the trans. This ring closure is prevented in the methyl ethers. If however conditions favour the hydrolysis of the ether group as when the compounds are heated with concentrated sulphuric acid coumarin formation takes place to some extent