Publication: Cyclophanes, XLVI oxidative carbon - carbon bond cleavage of a [2.2]paracyclophane derivative - efficient intramolecular trapping of the radical cation
Date
01-01-2000
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Abstract
4-(2,3,4,5-Tetraphenyl)phenyl[2.2]paracyclophane (3) has been prepared by cycloaddition of tetracyclone (2) to 4-ethynyl[2.2]paracyclophane (1). On treatment with FeCl3 or AlCl3 or NOBF4 in nitromethane, 3 undergoes C-C bond cleavage by an electron transfer process to provide the double benzyl radical cation 10. The phenyl groups of the aryl substituent are ideally oriented for intramolecular trapping and, in the presence of the Lewis acids, ring closure to the new phane system 5 takes place in good yield (65%). In the presence of NOBF4, the half-cyclized aldehyde 6 (66%) is produced. For comparison, [2.2]paracyclophane (7) was also treated with the latter one-electron oxidant, providing bibenzyl-4,4'-dicarbaldehyde (8, 30%) and its monooxime 9 (35%). The structures of the new phane systems 3 and 5 have been determined by X-ray structural analysis, and the mechanisms leading to these products are discussed.
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Aromatic polycycles, Cycloadditions, Phanes, Radical ions, Redox chemistry