Aktivierte Chinone: Substitution von Azulenen, Benzofuran und Indolen durch 2‐Methoxycarbonyl‐1,4‐benzochinon. Regiospezifische Synthesen von Polymethoxy‐fluorenonen und eine neue Synthese des 2,6‐Dihydro‐naphtho[1,2,3‐ cd ]indol‐6‐on‐Systems

Activated quinones: substitution reactions by methoxy‐carbonyl‐1,4‐benzoquinone of azulenes, benzofuran and indoles; regiospecific syntheses of polymethoxy‐fluorenones; a new synthesis of the 2,6‐dihydro‐naphtho[1,2,3‐ cd ]indol‐6‐one system. We present new electrophilic substitution reactions of azulenes and 5‐membered heterocyclics by methoxy‐carbonyl‐1,4‐benzoquinone. Hydroquinones 3a and 5 are prepared from azulene, and 3b from guaiazulene (see Scheme 1 ). Benzofuran undergoes α‐ and β‐substitution (hydroquinones 9 10 ) (see Scheme 2 ). Only β‐substitution is observed with indole (hydroquinone 20 ) (see Scheme 4 ). After methylation, saponification and intramolecular acylation of the substituted indoles 22c, 22d , derivatives of 2,6‐dihydro‐naphtho[1,2,3‐ cd ]indol‐6‐one have been obtained. Spectral data prove the presence of the methylidenequinone tautomer. By protonation or alkylation at the carbonyl group of 23 , the violet, highly delocalized 16π‐electron systems 25 are generated. Analogously, polymethoxy‐fluorenones have been prepared from methoxylated diphenylquinones 15 (see Scheme 3 ). They also are transformed by protonation and alkylation to the highly coloured and delocalized 12 π‐electron systems 18 . By contrast, anthracene is not substituted by methoxycarbonyl‐1,4‐benzoquinone, but undergoes cycloaddition to the triptycene derivative 1 (see Scheme 1 ). A summary is presented of previously described reactions of activated quinones.