PURPOSE: The reduction of indole-2,3-dione derivative with hydrogen sulfide in the presence of a base gives title compound under mild conditions in high yield resultingly with industrial advantage, which is useful as an intermediate for dichlorphnac, a nonsteroidal anti-inflammatory analgesic.
CONSTITUTION: An indole-2,3-dione derivate of formula I (R1, R3, R4 are H, Cl, Br; R2 is H,, lower alkyl) is reduced with hydrogen sulfide in the presence of a base as pyridine, morpholine, piperidine, aniline, n-butylamine, dimethyl-formamide to prepare 2-indolinon derivative of formula II. The reaction is preferably effected at a temperature of 0W10°C for 15 min to 48 hr.
EFFECT: The raw materials are readily available, expensive metal catalysts are unnecessary. The reaction finishes within a short time at low temperatures. The reaction yield is high. The isolation and purification of the product are simple because of no side reaction as dehalogenation.
NISHIMURA FUMIO
TAMAOKI KENTAROU
FUJII KIYOUICHI
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