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
Ah. Schmidt et al., 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, Synthesis, (4), 1994, pp. 422-426
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.