Oxokohlenstoffe und verwandte Verbindungen. 27. Synthese von Dihydrocyclobuta[a]naphthalen-1,2-dionen und Cyclobuta[a]naphthalen-1,2-dionen durch Anellierung von Alkoxy-(1-alkenyl)benzolen mit 3-Chlor-3-cyclobuten-1,2-dion. Anwendungsbereich und Grenzen

Abstract

Oxocarbons and Related Compounds. 27. Synthesis of Dihydrocyclobuta[a]naphthalene‐1,2‐diones and Cyclobuta[a]naphthalene‐1,2‐diones via Annulation of Alkoxy‐(1‐alkenyl)benzenes with 3‐Chloro‐3‐cyclobutene‐1,2‐dione. Scope and Limitations The reaction of alkoxy‐(1‐alkenyl)benzenes with semisquaric chloride (3) has been investigated systematically. 1,2‐Dialkoxy‐ and 1‐alkoxy'‐2‐alkoxy″‐4‐(1‐alkenyl)benzenes (6a–j) and (11a–i) react with 3 to give the 3,4‐dihydrocyclobuta[a]naphthalene‐1,2‐diones (8a–j) and (12a–i). Treatment of the dihydrocyclobuta[a]naphthalene‐1,2‐diones with 1.2 equiv. bromine effects dehydrogenation and affords cyclobuta[a]naphthalene‐1,2‐diones (9a–e) and (13b–f). Any efforts to extend this annulation reaction to dimethoxy‐(1‐alkenyl)benzenes with the methoxy groups in other than the 1,2‐positions, e. g. 14a, b, 16a, b have been unsuccessful. The reaction of 1,2,3‐trimethoxy‐4‐(1‐propenyl) [and 4‐(1‐butenyl)]‐benzenes (18a) and (18b) with semisquaric chloride (3) leads to the elimination of HCl and CH3OH and gives 5,6‐dimethoxy‐3‐methyl [and 3‐ethyl]‐cyclobuta[a]naphthalene‐1,2‐diones (20a) and (20b). The reaction pathway of this novel annulation reaction is discussed.