Protonated Porphyrins: Bifunctional Catalysts for the Metal-Free Synthesis of N-Alkyl-Oxazolidinones

The protonation of commercially available porphyrin ligands yields a class of bifunctional catalysts able to promote the synthesis of N-alkyl oxazolidinones by the CO2 cycloaddition to corresponding aziridines. The catalytic system does not require the presence of any Lewis base or additive and shows interesting features both in terms of cost-effectiveness and eco-compatibility. The metal-free methodology is active by using the low catalytic loading of 1% mol and the chemical stability of the protonated porphyrin allowed its recycle for three consecutive times without any decrease of performances. In addition, a DFT study was performed in order to suggest how a simple protonated porphyrin can mediate the CO2 cycloaddition to aziridines yielding oxazolidinones.