General synthetic entry to linearly-fused dihydrobenzocyclobutene-1,2-diones and benzocyclobutene-1,2-diones via annulation of 1,2-bis(methylene)carbocycles with 3-chloro-3-cyclobutene-1,2-dione

The tandem Diels-Alder/dehydrochlorination reaction of semisquaric chloride (1) with the 1,2-bis(methylene) cycloalkanes 2a-c and 1,2-bis (methylene)- 4-cyclohexene (9) affords the Linearly-fused cycloalkanodihydrobenzocyclobu tene-1,2-diones 3a-c and 3,4,7,8-tetrahydrocyclobuta[b]-naphthalene-1,2-dio ne (TO), respectively. On treatment with MnO2, 3a-c are dehydrogenated to t he respective carbocycle-fused benzocyclobutene-1,2-diones 4a-c in good yie lds. 3a and 3b react with bromine to give the addition products 5a,b, which , on treatment with silver trifluoroacetate, afford the benzocyclobutene-1, 2-diones 4a,b. For preparative purposes, the sequence 3 --> 5 --> 4 can be performed advantageously as a "one-pot procedure". Double-condensation reac tions of 4a,b with alpha,alpha'-biscyano-o-xylene and o-phenylenediamine af ford the pentacyclic biphenylenes 7a,b and the cyclobutahetarenes 8a,b, res pectively. These cyclobutenediones suggest themselves as building blocks fa r the construction of extended linearly-fused polycyclic compounds with nov el ring sequences. o-Quinodimethanes 12a-g generated in situ by the thermal decomposition of the respective 1,4-dihydro-2,3-benzoxathiin-3-oxides (sul tines) 11a-g react with semisquaric chloride (1) to afford the 3,8-dihydron aphtho[b]cyclobutene-1,2-diones 13a-g. These, on dehydrogenation with bromi ne and/or MnO2, furnish the naphtho[b]cyclobutene-1,2-diones 14a-g in fair to good yields. As described for 4a,b the naphtho[b]cyclobutene-1,2-diones 14a-c are condensed with alpha,alpha'-biscyano-o-xylene and o-phenylenediam ine to furnish the pentacyclic biphenylenes 15a-c and the pentacyclic cyclo butahetarenes 16a-c.