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

A cyclopentadienone iron tricarbonyl complex, able to harvest light and catalyze both dehydrogenation and reduction, allows the synthesis of γ,δ-unsaturated ketones using the borrowing hydrogen strategy in the presence of various substituted primary allylic or propargylic alcohols as alkylating reagents.

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.

N. Joly, A. Colella, M.-E. Mendy, M. Diagne Mbaye, S. Gaillard, A. Poater, J.-L. Renaud
ChemSusChem 2023, e202301472