Oxidative Carbon−Carbon Bond Cleavage of a [2.2]Paracyclophane Derivative − Efficient Intramolecular Trapping of the Radical Cation

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.

Synthesis and Optical Property Modulation of Substituted [2.2]Paracylophanes through Through‐Space Conjugation

“…In case of [2.2]paracyclophane, which bears 31-33 kcal/mol of strain energy, the homolytic cleavage of the ethano bridge becomes thermodynamically favourable owing to ring opening and the subsequent release of associated strain leading to biradicals formation above 200 °C. [48,49] In our study analysis of the DSC curve reveals exothermic behaviour for compound 3 and 4, while compound 5 exhibits endothermic behaviour. This suggests that compound 3 and 4 has lesser strain at the ethano bridges compared to compound 5, consequently 3 and 4 exhibiting resistance against homolytic thermal cleavage.…”

“…The thermal decomposition temperature (T d ) at which a 5 % weight loss occurred in a nitrogen atmosphere was determined to be 289 °C for 3 , 340 °C for 4 and 347 °C for 5 . In case of [2.2]paracyclophane, which bears 31–33 kcal/mol of strain energy, the homolytic cleavage of the ethano bridge becomes thermodynamically favourable owing to ring opening and the subsequent release of associated strain leading to biradicals formation above 200 °C [48,49] . In our study analysis of the DSC curve reveals exothermic behaviour for compound 3 and 4 , while compound 5 exhibits endothermic behaviour.…”

Redox-induced Diels–Alder revisited: impact of diene's oxidation on demanding cycloadditions

“…AgF 2 , WCl 6 or NO + salts cannot be used) and it should not induce undesirable side reactions (as typical of, e.g. , NOBF 4 34 ). Moreover, our tests with other common inorganic oxidizers such as Ce(SO 4 ) 2 , KMnO 4 and CoF 3 proved them too weak to oxidize anthracene (let alone its halogenated derivatives) and yielded less than 1% conversion for the anthracene–chalcone system.…”

Synthesis of [2.2]Paracyclophane/9-Alkylfluorene Hybrids and the Discovery of a Solvent-assisted Rearrangement

“…All attempts to convert 16 into the more highly π-extended cyclophane 17 using the Scholl reaction or photocyclization were unsuccessful, affording either unreacted starting material or TLC-immobile material. In the latter case, it is likely the [2.2]­paracyclophane unit suffered bridge cleavage under the oxidative conditions of the Scholl reaction …”

“…In the latter case, it is likely the [2.2]paracyclophane unit suffered bridge cleavage under the oxidative conditions of the Scholl reaction. 13 The structures of 7, 14, and 16 were determined using single-crystal XRD (Figure 2, Supporting Information). A common feature is that the CH−CH 2 bond is slightly longer (by 0.07−0.013 Å, >3σ) than the CH 2 −CH 2 bond in all three structures, and this is consistent with the aforementioned alignment of this σ bond with the adjacent π system.…”