Precision indole skeletal editing for single-carbon replacement.

C-labeled carbon into the scaffold. We highlighted the practical applicability of this method through a concise four-step total synthesis of quebrachamine, a complex monoterpene indole alkaloid. Experimental studies and density functional theory (DFT) calculations revealed a reaction pathway involving cascade [2+2] cycloaddition, retro-[2+2] ring opening, decarbonylation, and cyclization, elucidating the sequence at an atomic level.