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1. Formal [4 + 4]-, [4 + 3]-, and [4 + 2]-cycloaddition reactions of donor–acceptor cyclobutenes, cyclopropenes and siloxyalkynes induced by Brønsted acid catalysis

   https://doi.org/10.1039/d1sc00158b  

   Zheng, Haifeng; Wang, Rui; Wang, Kan; Wherritt, Daniel; Arman, Hadi; Doyle, Michael P. (April 2021, Chemical Science)

   null (Ed.)

   Brønsted acid catalyzed formal [4 + 4]-, [4 + 3]-, and [4 + 2]-cycloadditions of donor–acceptor cyclobutenes, cyclopropenes, and siloxyalkynes with benzopyrylium ions are reported. [4 + 2]-cyclization/deMayo-type ring-extension cascade processes produce highly functionalized benzocyclooctatrienes, benzocycloheptatrienes, and 2-naphthols in good to excellent yields and selectivities. Moreover, the optical purity of reactant donor–acceptor cyclobutenes is fully retained during the cascade. The 1,3-dicarbonyl product framework of the reaction products provides opportunities for salen-type ligand syntheses and the construction of fused pyrazoles and isoxazoles that reveal a novel rotamer-diastereoisomerism. 

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2. Comparison of the Photochemistry of Acyclic and Cyclic 4-(4-Methoxy-phenyl)-4-oxo-but-2-enoate Ester Derivatives

   https://doi.org/10.1021/acs.jpca.0c04319  

   Sarkar, Sujan K.; Upul Ranaweera, Ranaweera A.; Merugu, Rajkumar; Abdelaziz, Nayera M.; Robinson, Jendai; Day, Heidi A.; Krause, Jeanette A.; Gudmundsdottir, Anna D. (September 2020, The Journal of Physical Chemistry A)
3. Design, Synthesis and Aromaticity of an Alternating Cyclo[4]Thiophene[4]Furan

   https://doi.org/10.1002/chem.202300477  

   Kawakami, Manami; Sharma, Dhruv; Varni, Anthony_J; Tristram‐Nagle, Stephanie; Yaron, David; Kowalewski, Tomasz; Noonan, Kevin_J_T (May 2023, Chemistry – A European Journal)

   Abstract A new class of conjugated macrocycle, the cyclo[4]thiophene[4]furan hexyl ester (C4TE4FE), is reported. This cycle consists of alternating α‐linked thiophene‐3‐ester and furan‐3‐ester repeat units, and was prepared in a single step using Suzuki–Miyaura cross‐coupling of a 2‐(thiophen‐2‐yl)furan monomer. The ester side groups help promote asynconformation of the heterocycles, which enables formation of the macrocycle. Cyclic voltammetry studies revealed that C4TE4FE could undergo multiple oxidations, so treatment with SbCl₅resulted in formation of the [C4TE4FE]²⁺dication. Computational work, paired with¹H NMR spectroscopy of the dication, revealed that the cycle becomes globally aromatic upon 2e⁻oxidation, as the annulene pathway along the outer ring becomes Hückel aromatic. The change in ring current for the cycle upon oxidation was clear from¹H NMR spectroscopy, as the protons of the thiophene and furan rings shifted downfield by nearly 6 ppm. This work highlights the potential of sequence control in furan‐based macrocycles to tune electronic properties. 

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4. Discovery of n-Type Zintl Phases RbAlSb ₄ , RbGaSb ₄ , CsAlSb ₄ , and CsGaSb ₄

   https://doi.org/10.1021/acsaem.0c00048  

   Ortiz, Brenden R.; Gorai, Prashun; Braden, Tara; Bensen, Erik A.; Wilson, Stephen D.; Stevanović, Vladan; Toberer, Eric S. (March 2020, ACS Applied Energy Materials)
5. Structures and energetic properties of 4-halobenzamides

   https://doi.org/10.1107/S2053229618013463  

   Piontek, Aleksandra; Bisz, Elwira; Dziuk, Błażej; Szostak, Roman; Szostak, Michal (November 2018, Acta Crystallographica Section C Structural Chemistry)

   The amide bond represents one of the most fundamental functional groups in chemistry. The properties of amides are defined by amidic resonance (n N →π* C=O conjugation), which enforces planarity of the six atoms comprising the amide bond. Despite the importance of 4-halo-substituted benzamides in organic synthesis, molecular interactions and medicinal chemistry, the effect of 4-halo-substitution on the properties of the amide bond in N , N -disubstituted benzamides has not been studied. Herein, we report the crystal structures and energetic properties of a full series of 4-halobenzamides. The structures of four 4-halobenzamides (halo = iodo, bromo, chloro and fluoro) in the N -morpholinyl series have been determined, namely 4-[(4-halophenyl)carbonyl]morpholine, C 11 H 12 X NO 2 , for halo = iodo ( X = I), bromo ( X = Br), chloro ( X = Cl) and fluoro ( X = F). Computations have been used to determine the effect of halogen substitution on the structures and resonance energies. 4-Iodo- N -morpholinylbenzamide crystallized with a significant distortion of the amide bond (τ + χ N = 33°). The present study supports the correlation between the Ar—C(O) axis twist angle and the twist angle of the amide N—C(O) bond. Comparison of resonance energies in synthetically valuable N -morpholinyl and N -piperidinyl amides demonstrates that the O atom of the morpholinyl ring has a negligible effect on amidic resonance in the series. 

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