Trimethylindolenines as C–N synthons for the assembly of spiro[oxindole-thioxoimidazolidine-indoline] hybrids in formal [3+2] cycloadditions

Herein, previously unreported trimethylindolenines serving as useful C–N synthons in [3+2] cycloaddition reactions of donor–acceptor 3-isothiocyanato oxindoles to build a library of spiro[oxindole-thioxoimidazolidine-indoline] hybrids are described. A wide range of intriguing and complex products bearing three pharmacophores and three adjacent quaternary stereocentres were smoothly afforded in up to 92% yield, >20 : 1 dr, under catalyst-free conditions. Moreover, this strategy further expands the skeletal diversity of polyheterocycles, which will aid the search for new bioactive molecules.