Synthesis and stereochemical investigation of highly functionalized novel dispirobisoxindole derivatives via [3+2] cycloaddition reaction in ionic liquid

The reactivity pattern of E/Z isomerized (polaraziable Cdouble bond; length as m-dashC bond) alkyl 2-cyano-2-(2-oxoindolin-3-ylidene)acetate is studied with azomethine ylide generated in situ from decarboxylative condensation of isatin and sarcosine or proline yielding stereochemically different novel dispirobisoxindole derivatives with creation of up to four stereogenic centers through [3+2] cycloaddition reaction. Investigating the reaction with azomethine ylide of sarcosine, E isomer of alkyl 2-cyano-2-(2-oxoindolin-3-ylidene)acetate is taking part as a dipolarophile producing dispiropyrrolidine-bisoxindoles exclusively while in case of azomethine ylide of proline, Z isomer of alkyl 2-cyano-2-(2-oxoindolin-3-ylidene)acetate is participating to generate the dispiropyrrolizidine-bisoxindoles as single product in [bmim] BF4 ionic liquid as an environmentally benign solvent in excellent yields without using any catalyst. Good functional group tolerance and broad scope of usable substrates are other prominent features of the present methodology with high degree of chemo-, regio-, and stereoselectivity. The structure and relative stereochemistry of both types of cycloadducts were confirmed by single crystal X-ray diffraction as well as with the help of 1H, 13C, and HMBC spectroscopic techniques.