Concise preparation of spiro[indazole-3,3'-pyrrolidine]-2',5'-diones by a [3+2] cycloaddition between α-arylidene diazosuccinimides and in situ generated benzynes

An efficient [3+2] cycloaddition between α-arylidene diazosuccinimides and in situ generated benzynes has been developed for concise and stout preparation of spiro[indazole-3,3'-pyrrolidine]-2',5'-diones under mild conditions in good to excellent yields (up to 93% yield) within a few hours. For the introduction of an arylidene group, the multifunctional target spiro[indazole-3,3'-pyrrolidine]-2',5'-diones may boast potential biological activities for the indazole scaffold, and may be also used as potential new organic synthon for the preparation of new chemical and pharmaceutical entities. Successful scale-up preparation furtherly demonstrated the feasibility of our protocol.