Modulating Paratropicity in Heteroarene-Fused Expanded Pentalenes

Pentalenes are formally eight-π-electron antiaromatic, but π-expanded pentalenes can display varying levels of paratropicity depending on the choice of annelated (hetero)arenes and the geometry of π-expansion (i.e., linear vs bent topologies) around the [4n] core. Here, we explain the effects of annelation on the paratropicity of π-expanded pentalenes by relating the electronic structure of pentalenes to a pair of conjoined pentafulvenes

Organocatalytic Preparation of Substituted Cyclopentanes: A Mechanistic Study

The reaction mechanism of a tandem conjugate addition/α-alkylation of enals leading to functionalized cyclopentanes catalyzed by <i>O</i>-trimethylsilyldiphenylprolinol was investigated by mass spectrometry, NMR spectroscopy, and DFT calculations. We have shown that the high stereoselectivity of the reaction depends on the energy discrimination between the two stereoisomers formed by the condensation of the α,β-unsaturated aldehyde (cinnamaldehyde) and the catalyst. The stereoselectivity of this step depends on the solvent used. The experimental activation barriers were determined to be <i>E</i>_a = 25 ± 7 kJ mol^–1 (Arrhenius equation), Δ<i>H</i>^⧧ = 23 ± 7 kJ mol^–1, and Δ<i>G</i>^⧧ = 101 ± 9 kJ mol^–1 (Eyring equation)

Interplay of Charge and Aromaticity Upon Chemical Reduction of <i>p</i>‑Quinquephenyl with Alkali Metals

Chemical reduction study of a paraphenylene comprising five para-connected aromatic rings, namely, p-quinquephenyl (C30H22, 1), with alkali metals in THF revealed a facile formation of the doubly reduced anion, 12–, which was crystallized with different alkali metal counterions. Several products were characterized using single-crystal X-ray diffraction and spectroscopic methods. The use of different alkali metals allowed tuning of metal binding in the resulting crystalline products. The consequences of electron addition and metal complexation on the core of p-quinquephenyl were investigated with the help of computational methods. Most notably, reduction results in a shift from locally aromatic to quinoidal character of 12–, which is mitigated by complexation to the alkali metal cations

Interplay of Charge and Aromaticity Upon Chemical Reduction of <i>p</i>‑Quinquephenyl with Alkali Metals

Chemical reduction study of a paraphenylene comprising five para-connected aromatic rings, namely, p-quinquephenyl (C30H22, 1), with alkali metals in THF revealed a facile formation of the doubly reduced anion, 12–, which was crystallized with different alkali metal counterions. Several products were characterized using single-crystal X-ray diffraction and spectroscopic methods. The use of different alkali metals allowed tuning of metal binding in the resulting crystalline products. The consequences of electron addition and metal complexation on the core of p-quinquephenyl were investigated with the help of computational methods. Most notably, reduction results in a shift from locally aromatic to quinoidal character of 12–, which is mitigated by complexation to the alkali metal cations