Alkene Carboxy-Alkylation via CO

Herein, we introduce a new platform for alkene carboxy-alkylation. This reaction is designed around CO addition to alkenes followed by radical polar crossover, which enables alkylation through carbanion attack on carbonyl electrophiles. We discovered that CO adds to alkenes faster than it reduces carbonyl electrophiles and that this reactivity can be exploited by accessing CO via hydrogen atom transfer from formate. This photocatalytic system transforms vinylarenes and carbonyl compounds into a diverse array of substituted γ-lactone products. Furthermore, indoles can be engaged through dearomative carboxy-alkylation, delivering medicinally relevant C(sp)-rich heterocyclic scaffolds. Mechanistic studies reveal that the active photocatalyst is generated through a photochemically induced reaction between the precatalyst and DMSO. Overall, we have developed a three-component alkene carboxy-alkylation reaction enabled by the use of formate as the CO precursor.