Photo-Catalyzed Acyl Azolium Promoted Selective α-C(sp )-H Acylation of Acetone via HAT: Access to Thermodynamically Less Favoured (Z)-α,β-Unsaturated Ketones.

Mono α-acylation of acetone has been achieved for the first time by reacting with bench-stable acyl azolium salts under violet-LED light at room temperature. The intermolecular hydrogen atom transfer (HAT) from acetone to triplet state of azolium salts under violet LED irradiation resulted in thermodynamically less favourable (Z)-α,β-unsaturated ketones with up to 99 : 1 selectivity via C-C bond formation. This compelling protocol access the desired α-C(sp )-H acylation product under metal-, ligand- and oxidant-free conditions on a wide range of substrates.