A Catalyst-Free Self-Catalyzed [3+2] Cycloaddition Reaction of 3-Isothiocyanato Oxindoles and Vinylpyridines

A catalyst-free self-catalyzed [3+2] cycloaddition reaction of 3-isothiocyanato oxindoles with vinylpyridines has been established, affording the desired products in high yields (up to 97%) with moderate to good diastereoselectivities (up to 11:1) under mild conditions. The reaction mechanism has been investigated by control experiments, DFT calculations of pK(a) values and the kinetic studies, revealing that this reaction featured the mutual activation between 3-isothiocyanato oxindole and vinylpyridine to generate the reactive species. Furthermore, these products could be easily transformed into the corresponding methylated and hydroxylated products under basic conditions.