An object of the present invention is to industrially advantageously produce N-nitroisoureas or a salt thereof which is useful as a synthetic intermediate for pharmaceuticals and pesticides. The present invention relates to a process for producing a compound represented by the formula (2):
wherein R1, R2 and R3 are as defined below, or a salt thereof, which comprises reacting a compound represented by the formula (1):
wherein R1 represents an optionally substituted straight-chain or branched C1 to C6 alkyl group, R2 and R3 are the same or different and represent an optionally substituted straight-chain or branched C1 to C6 alkyl group, a cycloalkyl group or a substituted aryl group, or R2 and R3 simultaneously represent a hydrogen atom, or a salt thereof with a nitrating agent in the presence of sulfur trioxide.