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.