Synthesis of 2‑Formyl Carbazoles via Tandem Reaction of Indolyl Nitrones with 2‑Methylidene Cyclic Carbonate

The synthesis of functionalized carbazoles as privileged nitrogen heterocycles has emerged as a central topic in drug discovery and material science. We herein disclose the rhodium­(III)-catalyzed cross-coupling reaction between indolyl nitrones and 2-methylidene cyclic carbonate as an allylating surrogate, resulting in the formation of C2-formylated carbazoles via tandem C–H allylation, [3 + 2] cycloaddition, aromatization, and benzylic oxidation. The synthetic utility of this protocol is highlighted by a variety of post-transformations of C2-formylated carbazoles.