The invention relates to a method, which is based on the oxidative ring opening of a Compound with an oxindole structure, for producing substituted 2-(triazinylcarbonyl) sulfonanilides of formula (1-1) proceeding from an N-sulfonyl-substituted 3-triazinyl oxindole of formula (2-1), to the thus produced 2-(triazinylcarbonyl) sulfonanilides of formula (1-1), and to the use thereof as intermediate products for the synthesis of fine chemicals and active substances in the agricultural field. Furthermore, the invention relates to a multistage method for producing N-alkyl-N-[2-(l,3,5-triazin-2-ylcarbonyl)phenyl]alkansulfonamides of formula (4-1) proceeding from a 3-(alkylsulfanyl)-l,3-dihydro-2H-indol-2-on of formula (7-1), wherein the multistage method also has said oxidative opening as a sub-step, and to the 2-(triazinylcarbonyl) sulfonanilides of formula (1-1), said sulfonanilides being obtained by means of the oxidative ring opening and used as intermediates in the multistage method.
