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

Oxocarbons and Related Compounds. 27. Synthesis of Dihydrocyclobutaa]naphthalene-1,2-diones and Cyclobutaa]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-dihydrocyclobutaa]naphthalene-1,2-diones ( 8a–j ) and ( 12a–i ). Treatment of the dihydrocyclobutaa]naphthalene-1,2-diones with 1.2 equiv. bromine effects dehydrogenation and affords cyclobutaa]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]-cyclobutaa]naphthalene-1,2-diones ( 20a ) and ( 20b ). The reaction pathway of this novel annulation reaction is discussed.