The present review highlights advanced strategies to the synthesis of the chromones annulated with O-and N-containing heterocycles at C(7)-C(8) bond. Due to the prevalence of such motives in different kinds of natural flavonoids and some alkaloids, fused chromones have attracted a great deal of attention so far. On the other hand a wide range of biological activities is displayed by the compounds of this type both among naturally occurring flavonoids and their synthetic analogues. 8-Carbonyl-7-hydroxychromones proved to be versatile synthones for the synthesis of angular hetarenochromones via approach of annulation of a heterocycle to the chromone core. It also addresses the question of the biological activity of naturally occurring and fused synthetic hetarenochromones.
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The propensity of cyclic carboxylic anhydrides to undergo ring‐opening was exploited in a reaction with 2'‐hydroxy‐α‐heteroarylacetophenones leading to the formation of chromones. New simple method was developed for the synthesis of 2‐(ω‐carboxyalkyl)‐3‐heteroarylchromones without protecting either the phenolic or the carboxylic groups. Treatment with hydrazine led to the formation of 3(5)‐(ω‐carboxyalkyl)‐5(3)‐(2,4‐dihydroxyphenyl)‐4‐heteroarylpyrazoles.
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