Electrophilic 1,4-Addition of Carbon Dioxide and Aldehydes to Enones.

An umpoled electrophilic 1,4-addition to enones was achieved under photocatalytic conditions. Various enones reacted with CO 2 in the presence of an iridium photocatalyst and a benzimidazoline reductant under blue-light irradiation to give the corresponding γ-keto carboxylic acids. Aldehydes also coupled with enones under similar photocatalytic conditions to afford γ-keto alcohols (homoaldols) that were transformed into dihydrofurans and tetrahydrofurans through azeotropic posttreatments. Regioselective deuterium incorporation from D 2 O at the β-position demonstrated that 1,4-addition takes place via homoenolate anions.