The preparation and properties of small ring fused benzenes and naphthalenes

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Benzocyclobutene may be prepared by a three-step route first involving the Diels-Alder addition of butadiene to dimethylCyolobutene- 1,2-dicarboxylate. The resulting diester adduct may be hydrolyzed to the corresponding dicarboxylic acid which upon treatment with two equivalents of lead tetraacetate undergoes bis-decarboxylation and aromatization of the six-membered ring. By substituting different dienes into this scheme, a series of bis-annelated benzene isomers in which the benzene portion was fused to a four-, five- or six-membered ring has been prepared. When 1,1-dicyclobutenyl is used in this scheme, tricyclobutabenzene was obtained. The Diels-Alder addition of 1,2-dimethylenecyclobutane to dimethyl- cyclobutene-1,2-dicarboxylate provides the tricyclic diester 159. Pyrolysis promotes cyclobutene ring opening to diene 160 which can then be added to a second equivalent of dienophile to give the tetracyclic tetraester 161. Hydrolysis to tetraacid followed by oxidative decarboxylation and aromatization gives naphtho[b,e]dicyclobutene. [...]