One-shot indole-to-carbazole π-extension by a Pd–Cu–Ag trimetallic system

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We have developed a Pd–Cu–Ag trimetallic system that can convert indoles to carbazoles using electron-deficient alkenes as two-carbon units. Investigation of the reaction mechanism revealed that this one-shot indole-to-carbazole π-extension is likely to proceed through the sequence of (i) Pd/Cu-catalyzed indole C–H alkenylation, (ii) Ag-promoted Diels–Alder reaction and dehydrogenative aromatization. The successful one-pot synthesis of a granulatimide derivative, an interesting class of Chk1 kinase inhibitor, highlights the potential of the present reaction for further development and applications.