Metal-Free Synthesis of Oxindoles via (NH₄)₂S₂O₈-Mediated Halocarbocyclization of Alkenes in Water

Abstract

A metal-free synthesis of oxindoles was achieved through the (NH4)2S2O8-mediated halocarbocyclization of alkenes. This protocol provides a practical and environmentally benign method for the construction of halo-containing oxindoles in water. The advantages of this reaction are its good functional group tolerance and mild reaction conditions. On the basis of experimental observations, a plausible reaction mechanism is proposed.

Metal‐Free Synthesis of Oxazolidine‐2,4‐diones and 3,3‐Disubstituted Oxindoles via ICl‐Induced Cyclization

“…13 C NMR (100 MHz, CDCl 3 ): δ /ppm = 176.4, 140.8, 133.2, 127.6, 127.1, 122.2, 108.2, 47.9, 25.4, 21.9, 8.9. Spectral data are in agreement with literature values …”

Stereoselective Haliranium, Thiiranium and Seleniranium Ion‐Triggered Friedel–Crafts‐Type Alkylations for Polyene Cyclizations

“…In 2014, Guo and co‐workers developed a green and sustainable approach for the synthesis of halo‐functionalized oxindoles via (NH 4 ) 2 S 2 O 8 ‐mediated, halo‐induced Friedel–Crafts‐type cyclizations of N ‐arylacrylamides (Scheme ) . The use of (NH 4 ) 2 S 2 O 8 /NH 4 X (X=Cl, Br, I) in water afforded all three different halo‐substituted oxindoles in a good to excellent yields.…”

“…Recently, Zhang, Shi and Chen and their co‐workers developed the I 2 O 5 /KI reagent system for the iodo‐carbocyclization of similar types of substrates, namely N ‐arylacrylamides, in water to access iodo‐substituted oxindoles in good to excellent yields (Scheme ) . Like the reagent systems developed by Zhu and Guo, the I 2 O 5 ‐mediated strategy was also well suited for the synthesis of iodo‐substituted oxindoles. For the substrate scope, a wide variety of alkenes containing various electron‐rich and electron‐withdrawing groups as substituents of the aryl moiety all participated well in the reaction (yields=61–98%); however, with a stronger electron‐withdrawing substituent like NO 2 on the aryl group the respective alkene substrate completely failed to give the desired compound.…”

Iridium‐Catalysed Cascade Synthesis of Oxindoles Using Diazo Compounds: A Quick Entry to C‐7‐Functionalized Oxindoles

“…Unfortunately, most of these reported methods require prefunctionalized precursors or drastic reaction conditions . Furthermore, the majority of these reported methods deliver 3‐substituted or 3,3‐disubstituted oxindoles;, methods to prepare 3‐unsubstituted oxindoles are rather rare in the literature . Recently, direct C–H functionalization, a more benign and user‐friendly method, has been used to prepare this important scaffold.…”