Studies in the chemistry of benzobicyclo systems

Reactions of tetrahalogenobenzynes with certain tertiary arylamines afford products which are derived by both 1,2- and 1,4-cyclo-addition as well as from a betaine. The tetrahalogenobenzynes and benzyne react with eneamines to give benzocyclobutene-derivatives via betaines; the tetrahalogenobenzyne derivatives are readily hydrolysed to 2-tetrahalogenophenyl cycloalkanones. 1-N-alkylamino derivatives of 5,6,7,8-tetrahalogeno-1,4-dihydronaphthalene also undergo cleavage reactions in protic media. Thus, for example, 1-N, N-dimethylamino-tetrafluorobenzobarrelene gives 2,3,4,5- tetrafluoro-k'-N, N-dimethylaminobiphenyl in high yield and 1,2,3,1- tetrafluoro-5,8-dihydro-5,8-N-(-methyl)-iminonaphthalene affords 2'- (2,3,4,5-tetrafluorophenyl)-N-methyl. pyrrole. Apparent similarities between mass spectral and thermal processes have been investigated in connection with retro-Diels-Alder reactions leading to k, 5,6,7-tetrahalogeno-isobenzofurans and 1,5,6,7-tetrafluoro- 2-methylisoindole. These derivatives are more stable than the nonhalogenated compounds. The rearrangement reactions of 1-methoxybenzobarrelene derivatives in strong acids have been studied. Various possible mechanistic pathways have been investigated by deuterium labelling methods. Benzobicyclo[3.2.1] derivatives arise via a 2-carbonium ion while a 3-carbonium ion leads to benzobicyclo[2.2.2)dien-2-one derivatives. The solvolyses of certain toluene-p-sulphonates have been used to check mechanistic predictions. The position of protonation and the extent of the rearrangement can be controlled by the use of alkyl substituents. Thus 2,6-dimethyl-l-methoxytetrafluorobenzobarrelene affords only derivatives of benzobicyclo[3.2.1]- octadiene while 3,5-dimethyl-l-methoxy-tetrafluorobenzobarrelene gives products derived by rearrangement to the benzobicyclo[2.2.2] system.