Photoinduced, Metal-Free Hydroacylation of Aromatic Alkynes for Synthesis of α,β-Unsaturated Ketones via C(sp3)-H Functionalization
Ambuj Kumar Kushwaha, Arsala Kamal, Himanshu Kumar Singh, Suresh Kumar Maury, Tusar Mondal, Sundaram Singh*
*Department of Chemistry, Indian Institute of Technology (BHU), Varanasi 221 005, U.P., India,
Email: sundaram.apc
itbhu.ac.in
A. K. Kushwaha, A. Kamal, H. K. Singh, S. K. Maury, T. Mondal, S. Singh, Org. Lett., 2024, 26, 1416-1420.
DOI: 10.1021/acs.orglett.4c00031
Abstract
The use of MeCN:H2O as green solvent, Eosin Y as organic photocatalyst, and ambient air as oxidant enables a metal-free, reliable synthesis of α,β-unsaturated ketones from methyl arenes and aromatic alkynes. This reaction offers high efficiency, use of green solvents, metal-free nature, environmental friendliness, and visible light as a renewable energy source.
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Details
The article discusses a novel, metal-free photocatalytic method for the selective hydroxylation of benzylic methylenes to secondary alcohols using visible light. The process employs eosin Y as a photocatalyst, O2 as a green oxidant, and triethylamine to inhibit overoxidation. This method offers mild reaction conditions and yields secondary alcohols with 56-95% efficiency, making it environmentally friendly and cost-effective. The study highlights the importance of secondary benzylic alcohols in natural products and pharmaceuticals, noting that traditional synthesis methods are often tedious and limited by harsh conditions and toxicity. The new approach overcomes these challenges by using visible light to initiate the reaction, resulting in high selectivity and broad substrate scope. The method was tested on various substrates, including halogen-substituted indolines and N-substituted tetrahydroisoquinolines, demonstrating excellent yields and functional group tolerance. The article also includes a gram-scale experiment and structural modifications of benzylic-based molecules, showcasing the method's practical applicability. Control experiments suggest the involvement of radical intermediates and the necessity of oxygen in the reaction mechanism. This green catalytic scheme is expected to inform future efforts in natural product synthesis and derivatization.
Key Words
enones (acylation, oxidation), oxygen, photochemistry
ID: J54-Y2024
