REGIOSELECTIVE ANNULATION OF ALICYCLIC-AROMATIC DIENES WITH 3-HALO-3-CYCLOBUTENE-1,2-DIONES - SYNTHESIS OF ANNULATED ALPHA-HALOBENZOCYCLOBUTENONES

4-(1-Cycloalken-1-yl)-1,2-dialkoxybenzenes 8, 10, and 11 and 5-(1-cycl oalken-1-yl)-1,3-benzodioxoles 12-15 react with the semisquaric halide s 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 yie lds (20-76%). The reaction failed with alicyclic-aromatic dienes havin g no or only one alkoxy group in the benzene ring. The dehydrative ann ulation process could be extended to 4-(3,4-dimethoxyphenyl)-1,2-dihyd ronaphthalene (24), affording the highly annulated alpha-chlorobenzocy clobutenone 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 su ggested for the dehydrative annulation process. Several of the annulat ed alpha-halobenzocyclobutenones prepared were submitted to selected c hemical transformations. Thus, the reaction with tributyltin hydride a fforded the annulated benzocyclobutenones 26a-f in excellent yields (7 4-78%), and treatment with silver trifluoroacetate afforded the alpha- (trifluoroacetoxy)benzocyclobutenones 27a-c in 71-79% yields.