Macrocyclic polyether promoting vinylation of 2-pyrrolidone: Application and insight into mechanism

Abstract

Macrocyclic polyethers have the property of selectively complexing cations with unique applications in promoting reactions involving the participation of anion-cation pairs. However, the application of macrocyclic polyethers to promote base-catalyzed nucleophilic addition of acetylene has not been reported. This research demonstrates that 15-crown-5, 18-crown-6 and 2.2.2-crypt can be used as catalytic promoters to facilitate the KOH-catalyzed vinylation of 2-pyrrolidinone. It can be used to achieve one-step synthesis of N-vinyl pyrrolidone (NVP) from acetylene with effective reduction of solvent dosage. In particular, the addition of 2.2.2-crypt leads to a 29 % increase in the yield of NVP, where the promoting effect is better than that when the solvent dosage is doubled. Spectroscopic characterization and quantum chemical computations have shown that the mechanism of macrocyclic polyethers promotion of the process consists of two aspects. On the one hand, the basicity of KOH by complexing K⁺ is enhanced, which in turn promotes the deprotonation process of 2-pyrrolidinone. On the other hand, the complexation of K⁺ enhances the nucleophilicity of N atom in the anion of 2-pyrrolidone.