1968 Volume 41 Issue 12 Pages 2886-2894
The isomerization of several dimers of perchloro-(3,4-dimethylenecyclobutene) (I) has recently been reported by Fujino et al. Of these dimers, one (II) is transformed to other isomers (IIIa) and (IIIb) by means of pyrolysis at ca. 200°C. When heated to ca. 250°C, IIIa and IIIb are further converted into a fourth isomer (IV). The present X-ray study has revealed that II corresponds to perchloro-(3,4,7,8-tetramethylene-tricyclo[4.2.0.02.5]octane), as supposed from the chemical evidence, and IV, to perchloro-(4,8-dimethylene-tricyclo[3.3.2.01.5]deca-2,6-diene). It has been further established, from the results of the X-ray analysis of the dichloride of IIIa with the help of the chemical information, that IIIa and IIIb have the same two-dimensional chemical structure, perchloro-(3,4,7,8-tetramethylene-cycloocta-1,5-diene), rather than perchloro-(2,3,7,8-tetramethylene-bicyclo[4.2.0]octa-4-ene) which was speculated by Fujino et al., and that IIIa and IIIb are different from each other in the conformation of the cyclooctadiene ring. These structures for II, IIIa, IIIb, and IV give a reasonable explanation of the mechanism of the successive isomerization reactions mentioned above.
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