Protonation of the dienone oxygen activates the system for the dienone–phenol rearrangement. A neighbouring angular methyl group migrates from the ring junction to the adjacent carbon while π bonds reorganize. Loss of a proton restores aromaticity and furnishes the phenolic ring. The lactone portion retains its shown connectivity and stereochemistry. These changes, rather than simple enolization or complete aromatization of both rings, give A.
More Types of Reactions: Nucleophilic and electrophilic substitution reactions (both aromatic and aliphatic). Addition reactions to carbon-carbon and carbon-heteroatom (N and O) multiple bonds. Elimination reactions. Reactive intermediates – carbocation, carbanion, carbenes, nitrenes, arynes and free radicals. Molecular rearrangements. Barton decarboxylation and Barton-McCombie reaction, Hunsdiecker reaction. questions
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