Synthesis of Dispiro‐[indoline‐3,1'‐cyclopropane‐2',3''‐indoline]‐2,2''‐diones via Thermal [2+1] Cycloaddition Between 3‐Alkylidene‐7‐aza‐2‐indolones and 3‐Diazo‐7‐aza‐2‐oxindoles

Diastereoselective synthesis of highly substituted dispiro‐[indoline‐3,1'‐cyclopropane‐2',3''‐indoline]‐2,2''‐dione in excellent yield via an unusual catalyst‐free thermal [2+1]‐cycloaddition of E‐3‐alkylidene‐7‐aza‐2‐indolones and 3‐diazo‐7‐aza‐2‐oxindoles under neat condition has been developed. The advantages of the approach include mild reaction conditions, substrate tolerance, broad scope, high yields, and selectivity of the reaction. A plausible reaction mechanism invoking a carbene intermediate and alkene [2+1]‐cyclization is proposed.