An object is to provide a novel production method suitable for industrial production of a 3,3-dimethyl-3,4-dihydro-1H-quinoxalin-2-one derivative and a synthetic intermediate for the method. Provided is a method for producing a compound represented by formula (1): wherein R1 represents a hydrogen atom, an optionally substituted alkyl group, an optionally substituted cycloalkyl group, or an optionally substituted aryl group, R2 represents a hydrogen atom, an optionally substituted alkyl group, a hydroxy group, or nitrogen atom-protecting group, R3 represents a hydrogen atom, an optionally substituted alkyl group, a hydroxy group, or a nitrogen atom-protecting group, and X represents a hydroxy group or a leaving group, or a salt thereof, the method comprising the steps of: reacting a compound represented by formula (2): wherein R1, R2, and X are the same as defined in formula (1), R4represents an optionally substituted alkyl group, an optionally substituted cycloalkyl group, or an optionally substituted aryl group, or a salt thereof with a nitrating agent to obtain a compound represented by formula (3): wherein R1 , R2 , R4, and X are the same as defined in formulae (1) and (2), or a salt thereof, and reducing the compound represented by formula (3) or the salt therof to obtain the compound represented by formula (1) or the salt thereof.