Process for dyeing keratin fibres, preferably human keratin fibres such as the hair, comprising the application to said fibres: i) of at least one composition comprising at least one compound of formula below: and also the optical or geometrical isomers thereof, the tautomers thereof, the mineral or organic acid or base salts thereof, and the solvates thereof such as hydrates; in which formula: • R 1 represents i) a linear or branched (C 1 -C 6) alkyl group, such as methyl -CH 3, ii) -(C 1 -C 6) alk-O-H, preferably -CH 2 -O-H with (C 1 -C 6)alk representing a linear or branched C 1 -C 6 alkylene group; • R 2 represents an atom, ii) a group -C -R with R representing a hydrogen atom or a (C 1 -C 4) alkyl group such as -C -CH 3, iii) carboxyl -C -OH, iv) -C -O-(C 1 -C 6) alkyl, v) (di) (C 1 -C 6) (alkyl) aminocarbonyl such as -C -NH 2 or -C -N -(C 1 -C 6)alkyl; preferably -C -O-(C 1 -C 6)alkyl; • R 4 represents a hydrogen atom, ii) a linear or branched C 1 -C 4 alkyl radical, or iii) a benzyl radical; and • R 5 represents i) a hydrogen atom, ii) a linear or branched C 1 -C 6 alkyl group optionally substituted with a hydroxyl group, iii) a benzyl radical, iv) a hydroxycarbonyl radical -C OH, v) a -C -O-(C 1 -C 12) alkyl radical; in particular R 4 and R 5 represent a hydrogen atom; • X represents an oxygen atom; • n is 1 or 2; ii) at least one composition comprising at least one chemical oxidizing agent; the compositions and possibly being applied simultaneously, or sequentially by first applying and then applying; preferably composition is applied first, followed by applying to said fibres composition, after a waiting time of at least 5 minutes after applying composition. i) of at least one composition comprising at least one compound of formula below: and also the optical or geometrical isomers thereof, the tautomers thereof, the mineral or organic acid or base salts thereof, and the solvates thereof such as hydrates; in which formula: • R 1 represents i) a linear or branched (C 1 -C 6) alkyl group, such as methyl -CH 3, ii) -(C 1 -C 6) alk-O-H, preferably -CH 2 -O-H with (C 1 -C 6)alk representing a linear or branched C 1 -C 6 alkylene group; • R 2 represents an atom, ii) a group -C -R with R representing a hydrogen atom or a (C 1 -C 4) alkyl group such as -C -CH 3, iii) carboxyl -C -OH, iv) -C -O-(C 1 -C 6) alkyl, v) (di) (C 1 -C 6) (alkyl) aminocarbonyl such as -C -NH 2 or -C -N -(C 1 -C 6)alkyl; preferably -C -O-(C 1 -C 6)alkyl; • R 4 represents a hydrogen atom, ii) a linear or branched C 1 -C 4 alkyl radical, or iii) a benzyl radical; and • R 5 represents i) a hydrogen atom, ii) a linear or branched C 1 -C 6 alkyl group optionally substituted with a hydroxyl group, iii) a benzyl radical, iv) a hydroxycarbonyl radical -C OH, v) a -C -O-(C 1 -C 12) alkyl radical; in particular R 4 and R 5 represent a hydrogen atom; • X represents an oxygen atom; • n is 1 or 2; • R 1 represents i) a linear or branched (C 1 -C 6) alkyl group, such as methyl -CH 3, ii) -(C 1 -C 6) alk-O-H, preferably -CH 2 -O-H with (C 1 -C 6)alk representing a linear or branched C 1 -C 6 alkylene group; • R 2 represents an atom, ii) a group -C -R with R representing a hydrogen atom or a (C 1 -C 4) alkyl group such as -C -CH 3, iii) carboxyl -C -OH, iv) -C -O-(C 1 -C 6) alkyl, v) (di) (C 1 -C 6) (alkyl) aminocarbonyl such as -C -NH 2 or -C -N -(C 1 -C 6)alkyl; preferably -C -O-(C 1 -C 6)alkyl; • R 4 represents a hydrogen atom, ii) a linear or branched C 1 -C 4 alkyl radical, or iii) a benzyl radical; and • R 5 represents i) a hydrogen atom, ii) a linear or branched C 1 -C 6 alkyl group optionally substituted with a hydroxyl group, iii) a benzyl radical, iv) a hydroxycarbonyl radical -C OH, v) a -C -O-(C 1 -C 12) alkyl radical; in particular R 4 and R 5 represent a hydrogen atom; • X represents an oxygen atom; • n is 1 or 2; ii) at least one composition comprising at least one chemical oxidizing agent;