Double‐Sided Control of Product Type Preference in the Visible‐Light Initiated Reaction of 1,3‐Dicarbonyl Compounds with Alkenes

Abstract The demonstrated light‐initiated addition of radicals formed on an active methylene group to styrene derivatives exhibits a product selectivity influenced by the presence of a protic solvent. Under protic conditions, the predominant products are branched compounds with the alkene moiety attached to the methylene group. In the absence of a proton source, an alkene is incorporated between the carbonyl group and the methylene group, leading to the formation of products known from the De Mayo reaction. The utility of the presented method was confirmed by a broad substrate range of alkenes and compounds bearing active methylene groups. A comprehensive mechanistic study revealed that both types of products can be formed via the radical pathway. This suggests a previously unreported mechanistic pathway as an alternative to the De Mayo reaction, which gives the same type of products.