Oxocarbons and related compounds; Part 21. Diels-Alder reactions of 3-halogeno-3-cyclobutene-1,2-diones with 1,1'-bi-1-cycloalkenyls. Synthesis of dicycloalkano-annulated dihydrobenzocyclobutenediones and benzocyclobutenediones

Article abstract of DOI:10.1055/s-1994-25490

On controlled heating to 100°C, 3-chloro-3-cyclobutene-1,2-diones (5a) reacted with 1,1'-bi-1-cyclohexenyl (6) and 1,1'-bi-1-cyclopentenyl (13) to give the dicycloalkano-annulated dihydrobenzocyclobutenediones 7 and 16, respectively. Treatment of carbon tetrachloride solutions of 7 and 16 with bromine at reflux temperature afforded the corresponding benzocyclobutenediones 9 and 17. Surprisingly, the reaction of 5a with 1,1'-bi-1-cycloheptenyl (14) and 1,1'-bi-1-cyclooctenyl (15) gave directly the benzocyclobutenediones 20 and 21. The hitherto unknown 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% yield. Its reaction with the dienes 6, 13, 14 has been investigated.