Aqueous CO2 fixation: construction of pyridine skeletons in cooperation with ammonium cations

Abstract

A simple and green method is explored for the synthesis of fused pyridines by [2 + 2 + 1 + 1] the cycloaddition of ketones with an ammonium cation under a CO₂ atmosphere. The reactions employed ammonium cation as a nitrogen source and CO₂ gas as a carbon source in an aqueous solution. Monoethanolamine (MEA) was used as an additive to increase the solubility of CO₂ in an aqueous solution. The scope and versatility of the method are demonstrated with 38 examples. Products are found to be photosensitive and show potential applications as organic optoelectronic materials. A selectfluor-promoted reaction mechanism is proposed based on the experimental studies. Our work is superior as it is a metal-free system, uses CO₂ as a carbon source and MEA as an additive in aqueous synthesis.