Cyclooctatetraenoquinones. II. The synthesis and transformations of compounds related to dibenzo[a,e]cyclooctene-5,6,11(12H)-trione

Bromination of 11-acetoxydibenzo[a,e]cycloocten-5(6H)-one ( 6 ) gave the 6-bromo derivative ( 8 ), which on further bromination gave a hydrogen bromide adduct ( 12 or 13 ) of 6,6,12-tribromodibenzo[a,e]cyclooctene-5,11(6H,12H)-dione ( 14 ). Treatment of this adduct with aqueous-ethanolic ammonia followed by sublimation gave 11-oxoindeno[1,2-c]isocoumarin ( 4 ), not dibenzo[a,e]cyclooctene-5,6,11(12H)-trione ( 3 ) as earlier suggested. The conversion of 12 or 13 to 4 has been shown to involve the formation of 3-bromo-2-(o-carboethoxyphenyl)indone ( 17 ), which gave 4 and ethyl bromide on being heated at 180°. Oxidation of dibenzo[a,e]cyclooctene-5,11(6H,12H)-dione with selenium dioxide gave a bimolecular product 25 considered to be derived by loss of carbon monoxide from the dimer of dibenzo[b,ƒ]pentalene-5,10-dione ( 27 ), a selenium-containing product, 28 , and the hydrate 29 of 3 .