Synthesis of 5-Substituted Indole-2,3-dione

Substituted isonitroacetanilines 2 were prepared by the reaction of 4-substituted anilines 3 with chloral hydrate and hydroxylamine hydrochloride. 5-Substituted indol-2,3-dione 1 were prepared by the cyclization of 2 in the presence of concentrated sulfuric acid. 5-Substituted indol-2,3-dione 1 is an important intermediate in many biologically active compounds. The structure was confirmed by mass spectra (MS). Furthermore, the synthetic method was optimized. The total yield of the two steps was 51-68%(calculated from 4-substituted anilines).