The oxidation of 6-hydroxydopamine

Abstract

Abstract The oxidation of 6-hydroxydopamine (I) with molecular oxygen or potassium ferricyanide in aqueous solution has been shown to lead mainly to the formation of the uncyclized quinone 2-(β-aminoethyl)-5-hydroxy-p-benzoquinone (VII). However this quinone cyclized slowly, presumably to norepinochrome (i.e. indoline-5,6-quinone, XII), since 5,6-dihydroxyindole (II), known to be readily formed by rearrangement of norepinochrome (XII), can be isolated from these solutions. 5,6-Dihydroxyindolines (cf. XIII) can also be isolated (as their acetyl derivatives) from the products obtained by the addition of reducing agents to solutions containing 6-hydroxydopamine oxidation products. No evidence was found to suggest that the possible alternative cyclization of the quinone VII to the p-quinonoid aminochrome 6-hydroxyindoline-4,7-quinone (III) occurred to any significant extent.