1. Quantifying Through-Space Substituent Effects
Rebecca J Burns, Ioulia K Mati, Kamila B Muchowska, Catherine Adam, Scott L Cockroft Angew Chem Int Ed Engl. 2020 Sep 14;59(38):16717-16724. doi: 10.1002/anie.202006943. Epub 2020 Jul 17.
The description of substituents as electron donating or withdrawing leads to a perceived dominance of through-bond influences. The situation is compounded by the challenge of separating through-bond and through-space contributions. Here, we probe the experimental significance of through-space substituent effects in molecular interactions and reaction kinetics. Conformational equilibrium constants were transposed onto the Hammett substituent constant scale revealing dominant through-space substituent effects that cannot be described in classic terms. For example, NO2 groups positioned over a biaryl bond exhibited similar influences as resonant electron donors. Meanwhile, the electro-enhancing influence of OMe/OH groups could be switched off or inverted by conformational twisting. 267 conformational equilibrium constants measured across eleven solvents were found to be better predictors of reaction kinetics than calculated electrostatic potentials, suggesting utility in other contexts and for benchmarking theoretical solvation models.
2. Efficient synthesis of pentasubstituted pyrroles via intramolecular C-arylation
Barbora Lemrová, Michal Maloň, Miroslav Soural Org Biomol Chem. 2022 May 11;20(18):3811-3816. doi: 10.1039/d2ob00536k.
Immobilized L-aspartic acid beta-methyl ester (Fmoc-Asp(OMe)-OH) was reacted with 4-nitrobenzenesulfonyl chloride, followed by alkylation with various α-haloketones. The resulting intermediates were treated with potassium trimethylsilanolate, which yielded tetrasubstituted pyrroles after a one-step transformation consisting of sequential C-arylation, aldol condensation and spontaneous aromatization. The discovered synthetic strategy enables fast and simple access to pentasubstituted and functionalized pyrroles from a number of readily available starting materials.
3. Covalent Organic Frameworks Doped with Different Ratios of OMe/OH as Fluorescent and Colorimetric Sensors
Jilu Yang, Yuping Cao, Wenbo Si, Jin Zhang, Jiemin Wang, Yi Qu, Wenwu Qin ChemSusChem. 2022 Jun 8;15(11):e202200100. doi: 10.1002/cssc.202200100. Epub 2022 Apr 29.
Improving the luminescence properties of covalent organic frameworks (COFs) has always been an important issue. Here, a series of COFs (([OMe]x -TzDa (TzDa is composed only by monomerics Tz and Da, OMe represents the incorporation of monomeric Dm)) with different ratios of OMe and OH were designed and synthesized. The photochemical behavior of [OMe]x -TzDa changed significantly due to the synergistic effect of aggregation induced emission (AIE), intramolecular charge transfer (ICT), and excited-state intramolecular proton transfer (ESIPT) effects. [OMe]2 -TzDa, which contained a ratio of 2/1 of OMe/OH, showed the strongest fluorescence emission in water and the best linear relationship for the detection of pH. Furthermore, [OMe]2 -TzDa was used to monitor HCl and NH3 gases and showed a color change, visible to the naked eye. Therefore, a "confidential pigment" was successfully made. Moreover, [OMe]2 -TzDa was also applied to detect N2 H4 . The work indicates the [OMe]2 -TzDa can serve as the first fluorescence sensor to detect pH, HCl and NH3 gases, which also shows a good response to N2 H4 .
