Blue‐Light Induced Iron‐Catalyzed Synthesis of γ,δ‐Unsaturated Ketones

Abstract A visible‐light‐induced iron‐catalyzed α‐alkylation of ketones with allylic and propargylic alcohols as pro‐electrophiles is reported. The diaminocyclopentadienone iron tricarbonyl complex plays a dual role by harvesting light and facilitating dehydrogenation and reduction steps without the help of any exogenous photosensitizer. γ,δ‐Unsaturated ketones can now be accessed through this borrowing hydrogen methodology at room temperature. Mechanistic investigations revealed that the steric hindrance on the δ‐position of either the dienone or ene‐ynone intermediate is the key feature to prevent or decrease the competitive 1,6‐reduction (and consequently the formation of the saturated ketone) and to favor the synthesis of a set of non‐conjugated enones and ynones.