A highly regio- and stereoselective synthesis of 3-alkylidene-2-oxindoles has been described through a nucleophilic vinylic substitution (S N V) of (E)-3-(nitromethylene)indolin-2-one using pyrazol-3-ones as nucleophiles and Et 3 N as a base. The reaction affords selectively the Z-isomer when pyrazol-3-ones without substituents at the 4 position are used. While the reaction is E-selective with 4-substituted pyrazolones. The stereoselectivity (up to >20:1) and the yields (up to 98%) are very high under mild reaction conditions. (Figure presented.).
Vila, C., Slack, S., Blay, G., Muñoz, M. C., & Pedro, J. R. (2019). Regio- and Stereoselective Synthesis of 3-Pyrazolylidene-2-oxindole Compounds by Nucleophilic Vinylic Substitution of (E)-3-(Nitromethylene)indolin-2-one. Advanced Synthesis and Catalysis, 361(8), 1902–1907. https://doi.org/10.1002/adsc.201900048