Regioselective Annulation of Alicyclic−Aromatic Dienes with 3-Halo-3-cyclobutene-1,2-diones. Synthesis of Annulated α-Halobenzocyclobutenones1

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 α-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 α-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 α-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 α-(trifluoroacetoxy)benzocyclobutenones 27a−c in 71−79% yields.