OXOCARBONS AND RELATED-COMPOUNDS .21. DIE LS-ALDER REACTIONS OF 3-HALOGENO-3-CYCLOBUTENE-1,2-DIONES WITH 1,1'-BI-1-CYCLOALKENYLS - SYNTHESIS OF DICYCLOALKANO-ANNULATED DIHYDROBENZOCYCLOBUTENEDIONES AND BENZOCYCLOBUTENEDIONES

On controlled heating to 100 degrees C, 3-chloro-3-cyclobutene-1,2-dio nes (5a) reacted with 1,1'-bi-1-cyclohexenyl (6) and 1,1'-bi-1-cyclope ntenyl (13) to give the dicycloalkano-annulated dihydrobenzocyclobuten ediones 7 and 16, respectively. Treatment of carbon tetrachloride solu tions of 7 and 16 with bromine at reflux temperature afforded the corr esponding benzocyclobutenediones 9 and 17. Surprisingly, the reaction of 5a with 1,1'-bi-1-cycloheptenyl (14) and 1,1'-bi-1-cyclooctenyl (l5 ) gave directly the benzocyclobutenediones 20 and 21. The hitherto unk nown 3-bromo-3-cyclobutene-1,2-dione (5c) was prepared by treatment of 3-hydroxy-3-cyclobutene-1,2-dione (5b) with oxalic dibromide in 76% y ield. Its reaction with the dienes 6, 13, 14 has been investigated.