Metallaphotoredox Enabled Single Carbon Atom Insertion into Alkenes for Allene Synthesis

Efficient methods for synthesizing allenes from readily available starting materials pose a persistent challenge in organic chemistry. In this work, we present a novel two‐stage protocol for allene synthesis involving the single‐atom insertion into alkenes, facilitated by synergistic photoredox and cobalt catalysis. Diverging from conventional methods such as the Doering‐LaFlamme reaction, this photochemical rearrangement approach operates efficiently under mild conditions in a radical‐based manner. The protocol exhibits a broad substrate scope and demonstrates applicability in the late‐stage diversification of alkene‐containing natural products and bioactive molecules. Preliminary mechanistic studies and density functional theory (DFT) calculations offer insights into the reaction pathway, indicating a radical mechanism involving fleeting cyclopropyl carbene intermediates followed by rapid ring opening to form allenes.