Patent ID: 8669372

Claim:
A process for preparing a compound of formula (I) in which R 1 and R 2 are identical or different and are hydrogen; C 1 -C 8 -alkyl which is optionally substituted with one or more halogen, —OR 3 , or —COR 4 ; C 3 -C 7 -cycloalkyl which is optionally substituted with one or more halogen, C 1 -C 4 -alkyl, or C 1 -C 4 -haloalkyl; or aryl or aryl-(C 1 -C 4 -alkyl) each of which is optionally substituted with one or more halogen, C 1 -C 4 -alkyl, C 1 -C 4 -haloalkyl, —COR 4 , or sulphonylamino, R 3 is hydrogen, C 1 -C 4 -alkyl, C 1 -C 4 -alkylcarbonyl, or aryl, wherein the aryl is optionally substituted with one or more halogen, C 1 -C 4 -alkyl, or C 1 -C 4 -haloalkyl, R 4 is hydroxyl, C 1 -C 4 -alkyl, or C 1 -C 4 -alkoxy, comprising reacting a compound of formula (VI) in which R is R 1 or R 2 with an inorganic thiosulphate in a solvent or solvent mixture, wherein between 1.3 and 1.6 moles of thiosulphate are used per mole of dichloromaleimide of formula (VI).