Reaktionen von o ‐Chinonen mit Aminen und Proteinen. 4. Mitteilung . 7a‐Methyl‐5,6‐dioxo‐5,6,7,7a‐tetrahydroindol‐Derivate aus 4‐Methylbrenzcatechin und Enaminen

Reactions of o ‐Quinones with Amines and Proteins. 7a‐Methyl‐5,6,7,7a‐tetrahysroindole Derivatives from 4‐Methylcatechol and Enamines Methyl l‐[2′‐(methoxycarbonyl)ethyl]‐7a‐methyl‐5,6‐dioxo‐5.6.7,7a‐tetrahydro‐indole‐3‐carboxylate ( 1 ) was isolated after the oxidation of 4‐methylcatechol with silver ( 1 ) oxide in the presence of b̃‐alanine methyl ester in glacial acetic acid. The formation of 1 requires in situ dehydrogenation of the b̃‐aminocarboxylate and addition of the resulting enamine to 4‐methyl‐1,2‐benzoquinone. Reaction of ethyl 3‐(phenylamino)crotonate with 4‐methyl‐1,2‐benzoquinone afforded ethyl 2,7a‐dimethyl‐5,6‐dioxo‐1‐phenyl‐5,6,7,7a‐tetrahydroindole‐3‐carboxylate ( 6 ). Despite the fact that the yields are low, the addition of enamines to o ‐quinones represents an interesting novel extension of the Nenitzescu ‐reaction which is well known in the p ‐quinone series. Compound 1 may be considered as a novel model for the crosslinking of proteins by o ‐quinones. Formation of 1 was, however, not observed under physiological conditions.