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
