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.
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