Photoinduced Enantioselective Triplet Radical Reaction on Metal: Copper-Catalyzed Conjugate Addition of Acylsilanes to α,ß-Unsaturated Ketones and Aldehydes.

A photoinduced copper-catalyzed enantioselective conjugate addition of acylsilanes has been developed. The conjugate acylation of α,ß-unsaturated ketones and aldehydes was promoted by a copper(I)/chiral NHC catalyst under visible-light irradiation for synthesizing various 2-substituted 1,4-dicarbonyl compounds in enantioenriched forms. Mechanistic studies combining experiments and quantum chemical calculations indicated a reaction mechanism involving copper-to-acyl charge transfer (i.e., metal-to-ligand charge transfer (MLCT)) excitation of an alkene-bound acylcopper complex. The MLCT excitation is followed by an electronical and geometrical change to generate a ß-radical-C-enolate-Cu(II)-acyl complex with an acyl radical character, which undergoes facile C-C bond formation in the copper coordination sphere, affording the 1,4-conjugate addition product.

Photoinduced Platinum-Catalyzed Reductive Allylation of α-Diketones with Allylic Carbonates.

A unique process for the photoinduced platinum-catalyzed reductive allylation of α-diketones with allylic carbonates has been developed. This allylation reaction was found to proceed selectively at the more electron-deficient carbonyl group of the diketone to afford an α-keto homoallylic alcohol. Such products could be further derivatized by transformation of the remaining carbonyl group. A mechanistic investigation suggests that a ketyl radical generated in response to photoirradiation reacts with a (π-allyl)platinum complex to form a C-C bond.