Annulation reaction ring current

Because of their aromatic character, pyrones undergo annulation reactions and the introduction of substituents less readily than do most cyclic a,B-unsaturated carbonyl compounds. Nevertheless, some suitable modifications have been developed that allow these compounds to be used effectively in annulation reactions. Some reviews about synthesis of 2-pyrones with 3,4-fused carbocyclic ring systems are currently available (82S337 86G109 92T9111). 

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