Benzocyclo-octenes. part 4. Benzo- and dibenzo[a,e]-cycle-octene synthesis via benzocyclobutene

Abstract

The cycloadduct of benzocyclobutene with 2H-pyran-2-one readily undergoes thermal elimination of carbon dioxide and subsequent valence isomerisation to give benzocyclo-octene; analogous reactions of benzocyclobutene with alkyl and aryl derivatives of 2H-pyran-2-one and of thiophene 1, 1 -dioxide give benzocyclo-octenes directly at temperatures below 100 °C. The corresponding adducts of cyclo-penta-2,4-dienones are mostly more stable thermally, but undergo decarbonylation at higher temperatures. Dibenzo[a,e]cyclo-octenes have been obtained directly by reactions of benzocyclobutene with halogenated 1,2-quinodimethanes.