Use of ascorbic acid derivatives for dyeing keratin-containing fibres

A method for dyeing keratin-containing fiber comprising applying to the keratin-containing fiber a composition comprising at least one compound of the formula I or II or a salt thereof:

• wherein
• R1 or R2 each, independently of one another, denote hydroxyl, —O-alkyl, —OC(O)-alkyl, —PO3M or —O-glycosyl,
• alkyl denotes a straight-chain or branched alkyl group having 1 to 10 C atoms,
• M denotes an alkali or alkaline-earth metal cation or H,
• R3 or R4 each, independently of one another, stand for hydroxyl or a group of the formula III, with the proviso that at least one of the radicals R3 or R4 is of the formula III:
• where
• * indicates the point of attachment of the formula III group,
• R5 to R9 each, independently of one another, denote H, —OH, a straight-chain or branched alkoxy group having 1 to 20 C atoms, a fluorinated straight-chain or branched alkoxy group having 1 to 20 C atoms, -A, —NH2, —NHA, —NA2, —NH—(CH2—CH2—O)n—H, —N[(CH2—CH2—O)n—H]2, —[NHA2]X, —[NA3]X, —SO3H, —[SO3]X, 2H-benzotriazol-2-yl or —OC(O)-alkyl,
• A denotes a straight-chain or branched alkyl group having 1 to 20 C atoms and
• X is the counterion to the cations [NHA2]+ and [NA3]+ or the anion [SO3]−.