97. Deciphering the concerted PCET/decarboxylation pathway in photocatalyst-free acylation of activated alkenes to 1,4-dicarbonyls

Wen, J.;*† Zhao, L.;† Wang, Y.;† Jiang, Y.-Y.;* Yang, J.* Green Chem. 2026, 28, 9212–9218. Download Link

1,4-Dicarbonyl motifs are notoriously difficult to synthesize, yet the mechanistic underpinnings of conventional electron donor– acceptor (EDA) strategies remain contentious. Here, we unambiguously resolve this debate and disprove the hydrogenbonding EDA (H-EDA) mechanism for decarboxylative acylation of activated alkenes with α-keto acids, establishing a concerted proton-coupled electron transfer (PCET) pathway as the exclusive operative mechanism. A combination of spectroscopic, electrochemical, photophysical, and computational studies provides definitive evidence against EDA/H-EDA formation and electron transfer, while DFT calculations revealed an exceptionally low activation barrier for concerted PCET (ΔG‡/ΔE‡ = 5.1–11.6 kcal mol-1), consistent with high efficiency under mild conditions. This photocatalyst- and base-free visible-light protocol enables rapid assembly of diverse 1,4-dicarbonyl compounds, with broad substrate scope, exceptional functional group compatibility, and reliable gram-scale synthesis. This work not only delivers a practically sustainable route to 1,4-dicarbonyls but also corrects a pervasive mechanistic misunderstanding in catalyst-free photodecarboxylation, laying a general mechanistic foundation for the rational development of visible-lightmediated transformations.