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Towards the design of optically active thiophene S-oxides using quantum chemistry
摘要： The importance of axially chiral biaryls has risen steeply in the recent decades. This structural motif proved to be successful in catalytic asymmetric synthesis and the configuration of the biaryl axis is decisive for biological activity. A new approach for the atroposelective synthesis of biaryls would be through a cycloaddition between an enantiopure phenyl-substituted thiophene S-oxide and an alkyne. Importantly, the chiral center of the thiophene S-oxide needs to be stable enough to avoid pyramidal inversion during the cycloaddition. Since the racemization of thiophene monoxides has been scarcely investigated so far, we perform a thorough quantum chemical study on the inversion barriers of a large number of chiral thiophene S-oxide derivatives. Our main goal is to identify substitution patterns leading to stable atropisomers at room temperature. Appealingly, the role of the stereoelectronic effects and position of the substituents as well as the importance of aromaticity on the pyramidal inversion barrier is elucidated for the first time.
关键词： thiophene sulfoxides,axial chirality,DFT,enantiomerization,aromaticity
更新于2025-09-23 15:23:52
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Effect of arsenic coordination state on the structure, aromaticity, and optical properties of dithieno[3,2-b:2’,3’-d]arsoles
摘要： A silylated derivative of 4-phenyl-dithieno[3,2-b:2’,3’-d]arsole (DTAs) was synthesized, and the effect of coordinating of DTAs compounds to Pd on their structural and optical properties was investigated. Coordination of the As to Pd was found to increase the structural aromaticity of the ring system as measured by the harmonic oscillator measure of heterocyclic electron delocalization (HOMHED), and the pyramidalization of the As atoms was also found to show a good correlation with the HOMHED values. However, coordination had a more subtle impact on the optical properties than seen for phosphorus-containing analogues as the metal-ligand interactions were weaker.
关键词： aromaticity,arsenic,palladium complex,luminescence,dithienoarsole
更新于2025-09-10 09:29:36
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A 3-Dimensional Fully Conjugated Carbaporphyrin Cage
摘要： A fully conjugated 3-dimensional (3D) expanded carbaporphyrin (2) was prepared in a one-pot procedure that involves a reaction between a dibenzo[g,p]chrysene-bearing tetrapyrrole precursor (1) and pentafluorobenzaldehyde, followed by oxidation. Single crystal X-ray diffraction analysis revealed that 2 possesses a cage-like structure consisting of four dipyrromethenes and two bridging dibenzo[g,p]chrysene units. As prepared, 2 is nonaromatic as inferred from UV-vis-NIR and 1H NMR spectroscopy and a near-zero (-1.75) nucleus-independent chemical shift (NICS) value. In contrast, after protonation with trifluoroacetic acid (TFA), the cage gains global aromatic character as inferred from the large negative NICS value (-11.63) and diatropic ring current observed in the anisotropy of the induced current density (ACID) plot, as well as the ca. 8-fold increase in the excited state lifetime. In addition, the size of the cavity increases to ca. 143 ?3 upon protonation as deduced from a single crystal X-ray diffraction analysis. To our knowledge, this is the largest carbaporphyrin prepared to date and the first with a fully conjugated 3D cage structure whose size and electronic features may be tuned through protonation.
关键词： protonation,fully conjugated,cage-like structure,aromaticity switching,3D expanded carbaporphyrin
更新于2025-09-09 09:28:46