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A Pd-catalyzed decarboxylative dearomatization reaction of of a heterocyclic substrate enables access to an uncommon reaction intermediate, that rearomatizes in the presence of amine bases in a net C–H functionalization sequence. The dearomatized benzo[b]thiophene intermediate bears an exocyclic alkene that can be functionalized through cycloaddition and halogenation reactions to deliver complex heterocyclic products.