The invention relates to a cosmetic process for the depigmentation, lightening and / or bleaching of keratinous substances, in particular the skin, comprising the application of a cosmetic composition comprising a compound of formula (I): compound of formula (I ): or its tautomeric form of formula (I '): in which: R and R, identical or different, denote a radical chosen from: a) a hydrogen atom； b) a C 1 -C 6 alkyl group, optionally interrupted by N, S, or O, optionally substituted with one or more groups chosen from -OR, -SR, -NR R, -CHRHR； -COOR； an aryl group optionally substituted with one or more hydroxyls and / or with one or more C 1 -C 6 alkoxy radicals； c) a C 1 -C 6 alkyl group substituted with a C 1 -C 6 aryl radical optionally substituted with one or more hydroxyls and / or with one or more C 1 -C 6 alkoxy radicals) a phenyl group optionally substituted by one or more hydroxyl groups and / or with one or more C 1 -C 6 alkoxy radicals； R denoting H or a C 1 -C 5 alkyl group, R denoting H； a C -C hydrocarbon group； an acetyl group； R and R can form with the nitrogen atom which carries a ring selected from pyrrolidine, pyrroline, piperidine, piperazine, morpholine, thiomorpholine, azepine. The invention also relates to the cosmetic use of a compound (I) or (I) as a whitening, lightening and / or depigmenting agent for keratin materials.L'invention concerne un procédé cosmétique de dépigmentation, d'éclaircissement et/ou de blanchiment des matières kératiniques, notamment de la peau, comprenant l'application d'une composition cosmétique comprenant un composé de formule (I) : composé de formule (I) : ou sa forme tautomère de formule (l') : dans lesquelles : R et R , identiques ou différents, désignent un radical choisi parmi : a) un atome d'hydrogène ； b) un groupe alkyle en C -C , éventuellement interrompu par N, S, ou O , éventuellement substitué par un ou plusieurs groupes choisi(s) parmi -OR ,-SR , -NR R ,- CONHR ； -COOR ； un groupe aryle éventuellement s
