Dual Photoredox and Titanium Catalyzed Regioselective Allenylation of Aldehydes via Reductive Radical-Polar Crossover
Zulin Xiao , Wenzhe Shang , Tao Huang , Lei He , Jingyao Li , Shen Luo , Xiaoxia He , Xiang Li , Fusheng Li
Chinese Journal of Chemistry ›› 2025, Vol. 43 ›› Issue (3) : 275 -280.
Dual Photoredox and Titanium Catalyzed Regioselective Allenylation of Aldehydes via Reductive Radical-Polar Crossover
The direct reductive coupling of carbonyl compounds with propargyl halides is a powerful and reliable tool in the synthesis of α-allenols. However, stoichiometric metal reductants, harsh reaction conditions and a variety of additional additives are required in the traditional strategies. Additionally, the reactivity and regioselectivity control remains an elusive challenge. Herein, we developed the Ti-catalyzed regioselective reductive coupling of readily available aldehydes and racemic propargyl bromides to rapidly access a wide range of α-allenols. This method proceed efficiently in a reductive radical-polar crossover manner featuring mild conditions, excellent regioselectivity control, broad substrate scope, and eco-friendliness. Preliminary mechanistic studies support the radical-involved catalytic cycle. And the DFT calculations demonstrate that the regioselectivity is determined by the Zimmerman-Traxler-type transition states.
Photoredox catalysis / Titanium catalysis / α-Allenols / Regioselectivity / Reductive radical-polar crossover / C—C coupling
2024 SIOC, CAS, Shanghai, & WILEY-VCH GmbH
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