4-Pyrone ring degradation

Coumarin is degraded in the animal body by hydroxylation (Figure 3.3) [48,49, 56, 57, 59—61] in the rabbit, all six of the possible hydroxycoumarins are formed [49, 57, 62] although the major products are 3- (8) and 7-hydroxy-coumarins (9). The hydroxylation is followed by the opening of the a-pyrone ring via o-hydroxyphenylpyruvic (10) to yield finally o-hydroxyphenyllactic (11) and o-hydroxyphenylacetic acids (12). 

Pyrones, benzo[a]fluorenones s. 16, 821 4-Pyrone ring synthesis and degradation... 

The pyrone ring is opened by heating with aqueous alkalis [24,25], amines [151-155] or hydrazine [13, 157]. Much use has been made of the alkaline hydrolysis of chromones in the determination of structure [185, 186] for example, bromination of 7-hydroxychromone-2-carboxylic acid was shown to proceed at C-8 by degrading the product to 3-bromo-2,4-dihydroxyaceto-phenone (85) [25]. 

On the basis of experiments with sodium [l- C]acetate as precursor, Birch et al. (1958a) proposed that citromycetin (27) is derived from seven acetate units. Unfortunately, relatively few degradations are known for citromycetin, so the location of radioactive label was determined by direct measurement only for C(6) and certain carbon atoms located in the pyrone ring. For the remainder of the molecule, only minimal support was obtained for the proposed labeling pattern. 

Pyrone ring synthesis and degradation Double ring closure to condensed 4-pyrones... 

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