CARBON-CARBON BOND-CLEAVAGE OF THE [2.2]PARACYCLOPHANE RADICAL-CATION GENERATED BY ELECTRON-TRANSFER OXIDATION WITH CERIUM(IV) AMMONIUM-NITRATE

Single electron transfer (SET) oxidation of 12.2]paracyclophane (1) with cerium ammonium nitrate (CAN) produces the corresponding radical cation (1+.), which undergoes cleavage of the carbon-carbon bond of the ethano bridge to generate the double-benzylic radical cation 2+.. Trapping of this intermediate by oxygen and nucleophiles gives rise to aldehydes 3, while a second oxidation and subsequent nucleophilic trapping affords nitrates 4. This facile cleavage of the carbon-carbon bond is explained by alignment of the latter with the pi systems in the rigid structure of [2.2]paracyclophane, which enables charge delocalization across both benzene rings. When the reaction is carried out in methanol, aromatic substitution takes also place as a minor reaction pathway, which is responsible for the formation of the polyfunctionalized cyclophane 5d.