Metal-free radical nitration of the β C–H bond of 3-alkylidene-2-oxindoles with tert-butyl nitrite (TBN) has been explored. Interestingly, (E)-3-(2-(aryl)-2-oxoethylidene)oxindole and (E)-3-ylidene oxindole give different diastereomers on nitration. The mechanistic investigation revealed that the diastereoselectivity was controlled by the size of the functional group. Another transformation of 3-(nitroalkylidene) oxindole into 3-(tosylalkylidene) oxindole was performed through metal and oxidant-free tosylhydrazine-mediated sulfonation. Both methods have the advantages of readily available starting materials and operational simplicity.

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An efficient diastereoselective trans cyclopropanation of 3-alkylideneoxindole with in situ generated α-diazocarbonyl compound or α,β-unsaturated diazo compound under metal-free condition has been developed to synthesize 3-spirocyclopropyl-2-oxindolederivatives. The procedure is based on 1,3 -dipolar character of corresponding diazo compounds under base catalyzed condition. The method also has advantage of wide substrate scope and easily available starting materials.

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