Regioselective annulation of alicyclic-aromatic dienes with 3-halo-3-cyclobutene-1,2-diones.: Synthesis of annulated α-halobenzocyclobutenones

4-(1-Cycloalken-1-yl)-1,2-dialkoxybenzenes 8, 10, and 11 and 5-(1-cycloalken-1-yl)-1,3-benzodioxoles 12-15 react with the semisquaric halides 5a and 5b in a dehydrative annulation process to give the annulated alpha-halobenzocyclobutenones 9a,b and 16a,b-21a,b in poor to good yields (20-76%). The reaction failed with alicyclic-aromatic dienes having no or only one alkoxy group in the benzene ring. The dehydrative annulation process could be extended to 4-(3,4-dimethoxyphenyl)-1,2-dihydronaphthalene (24), affording the highly annulated alpha-chlorobenzocyclobutenone 25 in 50% yield. In the case of 5-(1-cyclobuten-1-yl)-1,3-benzodioxole (22), reaction with the semisquaric halides 5a,b yielded the dicyclobutanaphthodioxole-1,2-dione (23) as the sole product in a dehydrochlorinative annulation process. A reaction pathway has been suggested for the dehydrative annulation process. Several of the annulated alpha-halobenzocyclobutenones prepared were submitted to selected chemical transformations. Thus, the reaction with tributyltin hydride afforded the annulated benzocyclobutenones 26a-f in excellent yields (74-78%), and treatment with silver trifluoroacetate afforded the alpha-(trifluoroacetoxy)benzocyclobutenones 27a-c in 71-79% yields.