Heterocyclic compounds containing carbonyl groups, chemistry

The Chemistry of Unsaturated Nitrogen-Heterocyclic Compounds Containing Carbonyl Groups... 

The major part of this review concerns chromones which possess a carboxyl or related group at C-2 but a few derivatives of the 3-carboxylic acids are known and discussed. Compounds in which the heterocyclic oxygen or the pyrone carbonyl oxygen is replaced by sulphur are also mentioned. The chemistry of chromones has been reviewed up to 1948 [1] and a survey (without references) of the synthesis of coumarins and chromones of therapeutic interest appeared in 1970 [2], Naturally-occurring chromones are covered in a chapter of a book by Dean [3]. The chromone-2- and -3-carboxylic acids have not been reviewed previously, although an early review of chromones [4] contains a short section on chromone carboxylic acids. 

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