Breaking paracyclophane: the unexpected formation of non-symmetric disubstituted nitro[2.2]metaparacyclophanes

• Suraj Patel,
• Tyson N. Dais,
• Paul G. Plieger and
• Gareth J. Rowlands

Beilstein J. Org. Chem. 2021, 17, 1518–1526, doi:10.3762/bjoc.17.109

• intermediate or arenium ion 7 (Scheme 2). This occurs at the bridge as this offers greatest release of strain energy. Rearrangement to 8, as described by Cram and Hefelfinger, further lowers the strain energy of the cyclophane [36]. The carbocation could be trapped by a nitrate anion to give intermediate 9

Acid-catalyzed rearrangements in arenes: interconversions in the quaterphenyl series

• Sarah L. Skraba-Joiner,
• Carter J. Holt and
• Richard P. Johnson

Beilstein J. Org. Chem. 2019, 15, 2655–2663, doi:10.3762/bjoc.15.258

• . DFT computations with inclusion of implicit solvation support a complex network of phenyl and biphenyl shifts, with barriers to rearrangement in the range of 10–21 kcal/mol. Consistent with experiments, the lowest energy arenium ion located on this surface is due to protonation of m,p'-quaterphenyl

• . This supports thermodynamic control based on carbocation energies. Keywords: arenium ion; carbocation; density functional theory; microwave reaction; rearrangement; superacid; Introduction Carbocations are enigmatic reactive intermediates of enduring importance in chemistry. No other reactive species

• [20][21]. One classic example of arenium ion chemistry is the interconversion of terphenyl isomers 1–3 (Scheme 1). This rearrangement was first reported by Allen and Pingert in 1942 [22] and then independently rediscovered by Olah and Meyer twenty years later [23]. Interconversion of isomers 1–3 is

β-Hydroxy carbocation intermediates in solvolyses of di- and tetra-hydronaphthalene substrates

• Jaya S. Kudavalli and
• Rory A. More O'Ferrall

Beilstein J. Org. Chem. 2010, 6, 1035–1042, doi:10.3762/bjoc.6.118

• , namely that the arenium ion intermediates are strongly stabilised by hyperconjugation between the carbocationic charge centre and a β-C–H bond, and that this effect is amplified by the contribution of an aromatic structure to the no-bond resonance form (15b) of the valence bond representation of this

• interaction 15a↔15b in Scheme 4 [3]. The interaction operates effectively for arenium ion intermediates formed from alcohols (arene hydrates) and cis-dihydrodiols or their derivatives which, as illustrated in Scheme 5, can be formed in a conformation in which an axial C–H bond bond is positioned for