Synthetic experiments in the benzopyrone series

Summary

A review of ring isomeric change of flavones and chromones is made as also of the reactivity of C-hydroxy phloroglucinol and C-hydroxy phloracetophenone derivatives in methylation, benzoylation and ring closure. The results are consistent showing the greater reactivity of a hydroxyl group of the quinol unit as compared with that of the catechol unit. A tentative explanation is given.

A synthetic study has been made of the chromones ofEugenia caryophyllata. All the intermediates in the synthesis of eugenitin have now been isolated and fully characterised. A convenient route for the preparation of the starting material for this synthesis,viz., 3-methyl phloracetophenone has now been found. Two new syntheses of eugenin are also recorded. The observation of Schmid and Bolleter that eugenitin (6-methyl) undergoes change into isoeugenitol (8-methyl) when demethylated with boiling hydriodic acid and that isoeugenitin methyl ether (8-methyl) does not undergo isomeric change under the same conditions, is confirmed. This is the reverse of what has been observed in the case of C-hydroxy phloracetophenone derivatives. Further it is extraordinary because C-methyl phloroglucinol and C-methyl phloracetophenone behave like the C-hydroxy (methoxy) compounds in methylations and chromone ring closure.

An attempt has been made to develop a comprehensive scheme of biogenesis which includes all the five components occurring inEugenia caryophyllata. The basic compound is taken to be nor-eugenone and all the stages are based on analogy with laboratory experiments.