Isatins Gassman oxindole synthesis

Generally, the reaction works well for electron-deficient anilines. A modified approach using in situ prepared chlorosulfonium salts is preferred for more electron-rich anilines. Substituted thiol derivatives can be used to produce 3-oxindoles, which can be further reduced to 3-indole derivatives that are not available via the Gassman indole synthesis. The reaction is equally useful for the preparation of isatin derivatives vide infra). Historically, the Gassman oxindole synthesis has found applications in the preparation of heterocycles with medical or insecticidal properties. The reaction also has potential applications for the synthesis of oxindole containing natural products. ... 

As mentioned in the introduction, the Gassman oxindole synthesis is a good way to gain access to isatins. Historically, the isolated oxindoles were oxidized to the corresponding isatin using red mercuric oxide and boron trifluoride.These harsh and environmentally unfriendly conditions have been replaced by an air oxidation approach in which an in situ generated anion reacts with oxygen to make an intermediate peroxo radical that... 

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