Steric effects on the sydnones reactivity. New sydnones and pyrazoles

Abstract

The sydnones 7a,b and 8a-c gave the corresponding pyrazoles 9a-e by 1,3-dipolar cycloaddition with dimethyl acetylenedicarboxylate (DMAD). The highly sterically hindered 3-(4,6-dibromo-2-methylphenyl)-4-iodosydnone (8d) failed to react with DMAD on heating in boiling xylene. The iodination of sterically hindered sydnone 7b required more drastic reaction conditions than the sydnone 7a.