One-Pot Synthesis of Oxazolidinones and Five-Membered Cyclic Carbonates from Epoxides and Chlorosulfonyl isocyanate: Theoretical Evidence for the Asynchronous Concerted Pathway

The one-pot reaction of chlorosulfonyl isocyanate (CSI) with epoxides having substituted phenyl, benzyl and fused cyclic alkyl groups in different solvents under mild reaction conditions without additives and catalysts was studied. Oxazolidinones and five-membered cyclic carbonates were obtained with a ratio close to (1:1) in the cyclization reactions. The best reaction conversion for the synthesis of these compounds was carried out in dichloromethane (DCM). The method presented here has distinct advantageous over the existing methods such as one-pot reaction, shorter reaction times, metal-free reagent, good yields and very simple purification method. The mechanism for the cycloaddition reactions has been elucidated using density functional theory (DFT) method at the M06-2X/6-31+G(d,p) level. The investigation of the potential energy surfaces associated with two possible channels leading to oxazolidinones and five-membered cyclic carbonates revealed that the cycloaddition reaction takes place through an asynchronous concerted mechanism in gas phase and in DCM.