Crown ether as organocatalyst for reductive upgrading of CO2 to N-containing benzoheterocyclics and N-formamides

Constructions of heterocyclics by incorporation of CO2 into N-, O- and S-nucleophiles represent advance of synthetic methodology by using CO2 as a C1 feedstock. Herein, we reported crown ether (e.g. 18-crown-6)-catalyzed reductive functionalization of CO2 to various N-containing benzoheterocyclics and N-formamides in the presence of PhSiH3 under metal-free and mild conditions. Lewis acid–base interaction between PhSiH3 and 18-crown-6 enhanced hydride-donating ability of the PhSiH3, thus facilitating the CO2 insertion into the Si–H bond. A positive correlation was observed between electron-donating ability and catalytic activity of the investigated crown ethers on CO2 reduction. Crown ethers thus represent a novel organocatalytic activation model for CO2 reduction, demonstrating an important alternative for transition-metal-based catalysts.