Constitution of coumarinopyrones derived from 7-hydroxy- coumarins

When umbelliferon condenses with malic acid two isomeric compounds are formed. The angular coumarino-7:8-α-pyrone is the major product (95%) and its constitution is established from its preparation from umbelliferon-8-aldehyde by the Perkin's reaction. The second compound which should be the linear coumarino-7:6-α-pyrone is formed in a very small yield only (5%). Under the same conditions 4-methylumbelliferon produces only one compound whose constitution as 4-methylcoumarino-7:8-α-pyrone is arrived at from its independent synthesis from 4-methylumbelliferon-8-aldehyde. The constitution of this aldehyde is deduced not only from analogy but also from its reduction to 4:8-dimethyl-7-hydroxycoumarin which has been prepared from 2-methylresorcinol and ethylacetoacetate. 4-Methylumbelliferon and ethylacetoacetate also give only one compound which is given the constitution 4:4'-dimethylcoumarino-7:8-α-pyrone. This compound has been found to be produced in good yield from resorcinol and ethylacetoacetate in the presence of alcoholic hydrogen chloride. It is concluded that the angular isomer is the one invariably and most predominantly formed though the formation of the linear variety is not altogether precluded