Amino-cyclopropenium H-bonding organocatalysis in cycloaddition of glycidol and isocyanate to oxazolidinone

We developed a kind of neutral organocatalyst amino-cyclopropenium halide to facilitate the [3 + 2] cycloaddition of glycidol and isocyanate to prepare optical active oxazolidinone. Glycidol coupling with isocyanate followed by 5-exo-tet-type cyclization in the presence of organic ion pair. The mild H-bonding coordination between catalyst and substrate prevented the non-selective ring-opening of glycidols and racemization of products. Rather, the cation and anion species activated the epoxy sites and enhanced the nucleophile ability of amide sites, respectively. NMR titrations and control experiments demonstrated the crucial role of H-bonding in cycloaddition reactions. X-ray diffraction (XRD) verified the configuration of intermediate and product, indicating an S_N2 cyclization occurred in the process. HPLC analysis of the chiral oxazolidinones unveiled a high enantiomeric excess, signifying the ion pair has excellent stereochemical control. This work provided a simple, efficient, and large-scalable approach to synthesizing 4-hydroxymethyl oxazolidinones.