One-pot synthesis of novel 2-oxo(2H)-spiro[benzofuran-3,3′-pyrrolines] via 1,4-dipolar cycloaddition reaction

An efficient synthesis of novel spiro[2-oxobenzofuran-3,3′-pyrrolines] is achieved via a three-component 1,4-dipolar cycloaddition reaction at rt involving benzofuran-2,3-diones, dimethyl acetylenedicarboxylate along with imidazo[1,5-a]pyridine, or imidazo[1,5-a]quinoline or imidazo[5,1-a]isoquinoline. The expected isomeric benzofuro[3,2-f]oxazepines (kinetic control cycloadducts) were, however, not detected. Structures of the title spiro products are evidenced from HRMS and NMR spectral data and further confirmed by single-crystal X-ray crystallography.