From CO2 to CS2: a theoretical investigation of the cycloaddition to aziridines mediated by metal-free porphyrin-based catalytic systems

Abstract

A detailed computational analysis of the synthesis of thiazolidine-2-thiones by CS₂ insertion into three membered aziridine rings is here reported. DFT studies highlighted the feasibility of the atom-efficient process by employing either the metal-free binary TPPH₂/TBACl system or bifunctional TPPH₄Cl₂ molecules as the catalytic species. Detailed investigations into the mechanism promoted by the TPPH₂/TBACl system indicated, as in the analogous cycloaddition of CO₂, the pivotal role of the adduct between TPPH₂ and TBACl salts in the synthesis of both N-aryl and N-alkyl thiazolidine-2-thiones. The latter species can be also obtained by using the eco-compatible TPPH₄Cl₂ catalyst, which is able to simultaneously activate CS₂ and aziridine molecules. The comparison of the overall energy gains of the reaction between aziridines and CS₂ with respect to the same process involving CO₂ revealed that the formation of thiazolidine-2-thiones is more favoured than the synthesis of oxazolidin-2-ones paving the way to develop efficient and eco-compatible synthesis of thiazolidine-2-thiones.