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Pyrolysis and Isomerization Reactions of Multiply‐bridged Cyclophanes
Author(s) -
Hopf Henning,
Kleinschroth Jürgen,
Murad Abo ElFetouh ElSayed
Publication year - 1980
Publication title -
israel journal of chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.908
H-Index - 54
eISSN - 1869-5868
pISSN - 0021-2148
DOI - 10.1002/ijch.198000086
Subject(s) - cyclophane , chemistry , isomerization , pyrolysis , hydrocarbon , photochemistry , stereochemistry , organic chemistry , crystal structure , catalysis
When subjected to pyrolysis in para ‐di‐isopropylbenzene (270°C, 40h) [2.2.2] (1,2,4)cyclophane ( 5 ) is cleaved to 2,9‐dimethyldibenzo[a,e]cyclooctadiene ( 8 ). Under comparable conditions (290°C, 65h), [2.2.2.2] (1,2,3,5)cyclophane ( 6 ) is converted to 6,11‐dimethyl[2.2.2] (1,2,3)cyclophane ( 9 ), the first derivative of a symmetrical [2 n ]cyclophane carrying three consecutive ethano bridges. The isomeric [2.2.2.2]‐ (1,2,3,4)cyclophane ( 7 ), on the other hand, cannot be induced to undergo carbon‐carbon‐bond cleavage followed by hydrogen abstraction. Under the influence of aluminiumtrichloride/hydrogenchloride hydrocarbon 5 isomerizes to the unsymmetrical [2.2.2] (1,2,4) (1,2,5)cyclophane ( 10 ), whereas 6 and 7 are stable under these conditions. The thermal stability and propensity of multiply‐bridged cyclophanes to undergo isomerization reactions is discussed.