Controllable synthesis of 3-chloro- and 3,3-dichloro-2-oxindoles via hypervalent iodine-mediated chlorooxidation.

An efficient and controllable protocol for the synthesis of 3-chloro- and 3,3-dichloro-2-oxindoles has been developed via hypervalent iodine-promoted chlorooxidation. By using two equivalents of 1-chloro-1,2-benziodoxol-3-(1H)-one, a wide range of indoles were transformed into 3-chloro-2-oxindoles in DMF/CF3CO2H/H2O at room temperature with good yields. As far as we know, this is the first report on the selective C-2 oxidation and C-3 monochlorination of simple indoles. In addition, three equivalents of the same hypervalent iodine afforded 3,3-dichloro-2-oxindoles in up to 99% yields under optimized conditions (dioxane/H2O, 80 °C). The method features mild reaction conditions, the widespread availability of the substrates, and good functional group tolerance.