Development of catalyst-free approach to synthesize novel spiro[indoline-3,1′-pyrazolo[1,2-a]pyrazoles] via 1,3-dipolar cycloaddition

- A new series of spiro[indoline-3,1′-pyrazolo[1,2- a ]pyrazole] derivatives is reported - Isatin N,N′ ‑cyclic azomethine imines dipoles can be efficiently prepared by two different ways - A catalyst-free 1,3-dipolar cycloaddition approach was developed/optimized - Spiro[indoline-3,1′-pyrazolo[1,2- a ]pyrazole] derivatives in yields up to 77% - Crystalline structures of all cycloadducts were determined by single-crystal X-ray diffraction Spiro compounds are a class of naturally occurring organic molecules with a wide broad of applications in several fields, mainly in medicinal chemistry. Spirooxindoles have been considered by the scientific community as scaffolds for applications under medicinal purposes, namely as anticancer, antiviral, or antimicrobial agents. Due to this fact, the synthesis of spiro compounds, namely spirooxindoles is a hot topic in organic chemistry field. Herein, we report a catalyst-less synthesis of new spiro[indoline-3,1′-pyrazolo[1,2- a ]pyrazoles] via 1,3-dipolar cycloadditions of isatin N,N′ ‑cyclic azomethine imines with dimethylacetylenedicarboxylate (DMAD). A “library” of cycloadducts were obtained in good yields (59-77%) and were characterized by NMR spectral analyses and further confirmed by the single-crystal X-ray diffraction analysis of all the cycloadducts.