An agent for dyeing keratin fibers, in particular human hair, characterized in that it contains, in a cosmetic carrier, at least one compound of formula in which R1, R2, independently of one another, represent hydrogen, a C 1 -C 6 alkyl group, a C 2 -C 6 alkenyl group, a hydroxy group, a halogen, a C 1 -C 6 alkoxy group, an amino group, a nitro group, an acetylamino group or a sulfonamide group, or, provided they are in the ortho-position relative to one another, R1 and R2 form a 5 or 6 member saturated or unsaturated ring that may optionally contain additional heteroatoms, X represents O or N-R3, R3 represents hydrogen, a C 1 -C 6 alkyl group, a C 2 -C 6 alkenyl group, a C 2 -C 6 hydroxy alkyl group, a C 2 -C 6 polyhydroxy alkyl group, a cyano C 1 -C 6 alkyl group or a group -Y'-O-SO 2 -O-M +, Y, Y' independently of one another each represent (CH 2) n or C 2 H 4 -(OC 2 H 4) n or (CH 2) n -O-(CH 2) m or (CH 2) n -N(R6')-(CH 2) m, and n and optionally m each represent an integer from 1 to 6, A represents one of the structures to, or R4, R5 independently of one another each represent hydrogen, an amino group, a C 1 -C 6 alkyl amino group, a di-(C 1 -C 6 -alkyl) amino group, a hydroxy group, a C 1 -C 6 alkoxy group, a C 1 -C 6 alkyl group, a C 2 -C 6 alkenyl group, a carboxylic acid group, a sulfonic acid group, halogen, an acetyl amino group or a sulfonamide group, or, provided they are in the ortho-position relative to one another, R4 and R5 form a 5 or 6 member saturated or unsaturated ring that may optionally contain additional hetero atoms, R6, R6' independently of one another each represent a hydrogen atom, a C 1 -C 6 alkyl group, a C 2 -C 6 alkenyl group or a C 2 -C 6 hydroxy alkyl group, and M + represents a proton (H +), an alkali metal cation or a half-equivalent of an alkaline earth metal cation. R1, R2, independently of one another, represent hydrogen, a C 1 -C 6 alkyl group, a C 2 -C 6 alkenyl group, a hydroxy group, a halogen, a C 1 -C 6 alkoxy group, an amino group, a nitro group, an acetylamino group or a sulfonamide group, or, provided they are in the ortho-position relative to one another, R1 and R2 form a 5 or 6 member saturated or unsaturated ring that may optionally contain additional heteroatoms, X represents O or N-R3, R3 represents hydrogen, a C 1 -C 6 alkyl group, a C 2 -C 6 alkenyl group, a C 2 -C 6 hydroxy alkyl group, a C 2 -C 6 polyhydroxy alkyl group, a cyano C 1 -C 6 alkyl group or a group -Y'-O-SO 2 -O-M +, Y, Y' independently of one another each represent (CH 2) n or C 2 H 4 -(OC 2 H 4) n or (CH 2) n -O-(CH 2) m or (CH 2) n -N(R6')-(CH 2) m, and n and optionally m each represent an integer from 1 to 6, A represents one of the structures to, or R4, R5 independently of one another each represent hydrogen, an amino group, a C 1 -C 6 alkyl amino group, a di-(C 1 -C 6 -alkyl) amino group, a hydroxy group, a C 1 -C 6 alkoxy group, a C 1 -C 6 alkyl group, a C 2 -C 6 alkenyl group, a carboxylic acid group, a sulfonic acid group, halogen, an acetyl amino group or a sulfonamide group, or, provided they are in the ortho-position relative to one another, R4 and R5 form a 5 or 6 member saturated or unsaturated ring that may optionally contain additional hetero atoms, R6, R6' independently of one another each represent a hydrogen atom, a C 1 -C 6 alkyl group, a C 2 -C 6 alkenyl group or a C 2 -C 6 hydroxy alkyl group, and M + represents a proton (H +), an alkali metal cation or a half-equivalent of an alkaline earth metal cation.