Cyclophanes, XLVI - Oxidative carbon-carbon bond cleavage of a [2.2]paracyclophane derivative - Efficient intramolecular trapping of the radical cation

4-(2,3,4,5-Tetraphenyl)phenyl[2.2]paracyclophane (3) has been prepared by c ycloaddition of tetracyclone (2) to 4-ethynyl[2.2]paracyclophane (1). On tr eatment with FeCl3 or AlCl3 or NOBF4 in nitromethane, 3 undergoes C-C bond cleavage by an electron transfer process to provide the double benzyl radic al cation 10. The phenyl groups of the aryl substituent are ideally oriente d 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 comp arison, [2.2]paracyclophane (7) was also treated with the latter one-electr on oxidant, providing bibenzyl-4,4'-di-carbaldehyde (8, 30%) and its monoox ime 9 (35%). The structures of the new phane systems 3 and 5 have been dete rmined by X-ray structural analysis, and the mechanisms leading to these pr oducts are discussed.