Oxindoles special

The C-2 and C-3 hydroxy derivatives of pyrrole are special in the sense that the tautomeric equilibria favor the pyrrolinone structures (see Section 3.04.6.2). Furthermore, the general synthetic methods are not usually applicable so that we will call attention in this section not only to the methods of directly introducing these substituents, which are rare, but also to those ring construction processes which specifically give the pyrrolinones and indolinones. The indole derivatives have widely used trivial names, oxindole (5) for indolin-2-one and indoxyl (6) for indolin-3-one, Carbocyclic hydroxy substituents in indole and carbazole, on the other hand, for the most part act as normal aromatic phenolic groups. These compounds are usually prepared by application of the standard ring syntheses. 

Intramolecular nucleophilic substitution by the anions of o-haloanilides is another viable oxindole synthesis. This is a special example of the category Ic process described in Section 3.06.2.3. The reaction is photo-stimulated and the mechanism is believed to be of the electron-transfer type SRN1 rather than a classical addition-elimination mechanism. The reaction is effective when R = H if 2 equivalents of the base are used to generate the dianion (equation 202) (80JA3646). 

---