OXOCARBONS AND RELATED-COMPOUNDS .27. SYN THESIS 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 gi ve 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] napht halene-1,2-diones (9a-e) and (13b-f). Any efforts to extend this annul ation reaction to dimethoxy-(l-alkenyl)benzenes with the methoxy group s in other than the 1,2-positions, e. g. 14a, b, 16a, b have been unsu ccessful. The reaction of 1,2,3-trimethoxy-4-(l-propenyl) [and 4-(1-bu tenyl)]-benzenes (18a) and (18b) with semisquaric chloride (3) leads t o the elimination of HCl and CH3OH and gives 5,6-dimethoxy-3-methyl [a nd 3-ethyl]-cyclobuta[a]naphthalene-1,2-diones (20a) and (20b). The re action pathway of this novel annulation reaction is discussed.