The oxidation of 6-hydroxydopamine

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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.