Article
Chemistry, Multidisciplinary
Jonathan Kirschner Solberg Hansen, Christian G. Tortzen, Preben Graae Sorensen, Mogens Brondsted Nielsen
Summary: This article elucidates the mechanism of the [2+2] cycloaddition - retro-electrocyclization reaction through detailed kinetics studies using H-1 NMR spectroscopy. By considering multiple experiments, it was found that the autocatalysis model with the final product promoting the first step best described the experimental data. Transient cyclobutene was successfully generated and confirmed as an intermediate through proper choice of conditions.
CHEMISTRY-A EUROPEAN JOURNAL
(2022)
Article
Chemistry, Multidisciplinary
Jelte P. Nimoth, Thomas Mueller
Summary: Hydrogen-bridged oligosilanylsilyl borates and diborates were prepared through hydride transfer. Their structures and properties were characterized using low temperature NMR spectroscopy and density functional calculations.
CHEMISTRY-A EUROPEAN JOURNAL
(2022)
Article
Chemistry, Multidisciplinary
Niklas Radhoff, Constantin G. G. Daniliuc, Armido Studer
Summary: The design, synthesis, and application of benzene bioisosteres have been a subject of great interest in the past two decades. Recently, bicyclo[2.1.1]hexanes have been established as highly attractive bioisosteres for ortho- and meta-substituted benzenes. In this study, we present a mild, scalable, and transition-metal-free method for constructing highly substituted bicyclo[2.1.1]hexan-2-ones through Lewis acid-catalyzed (3+2)-cycloaddition of bicyclo[1.1.0]-butane ketones with disubstituted ketenes. The reaction exhibits high functional group tolerance, as evidenced by the successful synthesis of various 3-alkyl-3-aryl and 3,3-bisalkyl bicyclo[2.1.1]hexan-2-ones (26 examples, up to 89% yield). Additionally, postfunctionalization of the exocyclic ketone moiety is demonstrated.
ANGEWANDTE CHEMIE-INTERNATIONAL EDITION
(2023)
Article
Chemistry, Multidisciplinary
Danila O. Zakharov, Konstantin Chernichenko, Kristina Sorochkina, Shengjun Yang, Ville-Veikko Telkki, Timo Repo, Vladimir V. Zhivonitko
Summary: In this study, we report the nuclear spin hyperpolarization of various alkenes achieved through alkyne hydrogenations with a metal-free hydroborane catalyst. The specific spin dynamics in catalytic intermediates leads to the hyperpolarization of one hydrogen in the alkene, allowing for advanced characterization of the catalytic process.
CHEMISTRY-A EUROPEAN JOURNAL
(2022)
Article
Chemistry, Organic
Kai Matsui, Kohei Toh, Manabu Hatano, Kazuaki Ishihara
Summary: A multiselective Diels-Alder reaction involving alpha-arylacroleins and cyclopentadiene has been developed using BBr3-assisted chiral BINOL-derived phosphoric acid catalysts. The chiral cavity of the in situ-formed acid-base cooperative catalysts plays a key role in controlling the exo- and enantioselectivity, particularly by suppressing the competitive hetero Diels-Alder reaction effectively.
Article
Chemistry, Organic
Prasoon Raj Singh, Pratibha Kalaramna, Shamsad Ali, Avijit Goswami
Summary: A simple protocol has been developed to access thio-/selenopyrrolines through a (3+2)-cycloaddition reaction using SnCl4 as a Lewis acid catalyst. Good chemoselectivity was observed when DACs were treated, indicating that thiocyanate is more reactive than nitrile moiety in such reactions.
EUROPEAN JOURNAL OF ORGANIC CHEMISTRY
(2021)
Article
Chemistry, Multidisciplinary
Anna Berlicka, Paulina Forys-Martowlos, Michal J. Bialek, Katarzyna Stasiak, Aleksandra Walczak, Agnieszka Wojcik, Agata Bialonska, Lechoslaw Latos-Grazynski
Summary: The oxidation of 10,15-diaryl-21-carba-23-selenaporphyrinoids resulted in the formation of dyads. The dimerization process followed a [5+2] cycloaddition path, leading to the formation of an azepine unit. The unique arrangement of two carbaporphyrinoid planes resembling an open seashell-like motif was observed in the covalently linked selenacarbaporphyrinic dyads, formed via the [5+2] cycloaddition reaction.
ANGEWANDTE CHEMIE-INTERNATIONAL EDITION
(2023)
Article
Chemistry, Multidisciplinary
Tim Steinke, Patrick Wonner, Richard M. Gauld, Sascha Heinrich, Stefan M. Huber
Summary: This study investigates the activation of imines in a Povarov reaction using bidentate cationic chalcogen bond donors. Tellurium-based Lewis acids show superior catalytic properties compared to selenium-based catalysts. The activity of the chalcogen bonding donors is influenced by the strength of the binding anions, and the choice of solvent and catalyst affects the diastereomeric ratio of the product.
CHEMISTRY-A EUROPEAN JOURNAL
(2022)
Article
Multidisciplinary Sciences
Cristina Di Carluccio, Rosa Ester Forgione, Marco Montefiori, Monica Civera, Sara Sattin, Giovanni Smaldone, K. Fukase, Y. Manabe, Paul R. Crocker, Antonio Molinaro, Roberta Marchetti, Alba Silipo
Summary: Siglecs are a group of cell-surface receptors belonging to the I-type lectin family, mostly expressed on innate immune cells, among which CD22 plays a key role in maintaining tolerance and preventing autoimmune responses. This study focused on the interaction of CD22 with sialoglycans, specifically exploring the role of N-glycolyl neuraminic acid (Neu5Gc) in this process. Findings suggested a comparable molecular recognition profile between human and murine forms of CD22, providing insights for innovative diagnostic and therapeutic methodologies in immune response modulation.
Article
Chemistry, Multidisciplinary
Martin T. Peschel, Piotr Kabacinski, Daniel P. Schwinger, Erling Thyrhaug, Giulio Cerullo, Thorsten Bach, Juergen Hauer, Regina de Vivie-Riedle
Summary: Lewis acids have been recognized as catalysts for enantioselective photochemical transformations, but mechanistic studies on these systems are rare. This work overcomes the challenges by using sub-30-fs transient absorption in the UV and accurate theoretical treatment. Investigations on the 2-cyclohexenone and boron trifluoride complex reveal that the Lewis acid remains attached to the substrate in the triplet state, leading to high enantioselectivity.
ANGEWANDTE CHEMIE-INTERNATIONAL EDITION
(2021)
Article
Chemistry, Multidisciplinary
Eveline H. H. Tiekink, Pascal Vermeeren, Trevor A. A. Hamlin
Summary: We investigated the uncatalyzed and Lewis acid (LA)-catalyzed cycloaddition reaction between tropone and 1,1-dimethoxyethene using dispersion-corrected relativistic density functional theory (DFT). The LA catalysts BF3, B(C6H5)(3), and B(C6F5)(3) effectively accelerated both [4+2] and [8+2] cycloaddition reactions by lowering the activation barrier by up to 12 kcal mol(-1) compared to the uncatalyzed reaction. Our study revealed that the LA catalyst promoted the cycloaddition reaction pathways through LUMO-lowering catalysis and demonstrated that Pauli-lowering catalysis is not always the operative mechanism in cycloaddition reactions. Selecting the appropriate LA catalyst allowed for regiocontrol of the cycloaddition: B(C6H5)(3) yielded the [8+2] adduct while B(C6F5)(3) produced the [4+2] adduct. The regioselectivity shift was found to be due to the LA's ability to absorb distortion and adopt a trigonal pyramidal geometry around the boron atom.
CHEMISTRY-A EUROPEAN JOURNAL
(2023)
Article
Chemistry, Organic
Grzegorz Mloston, Mateusz Kowalczyk, Andre U. Augustin, Peter G. Jones, Daniel B. Werz
Summary: The reactivity of donor-acceptor cyclopropanes towards thioketenes was investigated, leading to the formation of exocyclic thioenol ethers in moderate to good yields in a (3+2)-cycloaddition using Sc(OTf)(3) as a Lewis acidic catalyst. Unsymmetrical thioketenes provided E/Z mixtures at the double bond, with the Z isomer being preferred.
EUROPEAN JOURNAL OF ORGANIC CHEMISTRY
(2021)
Article
Chemistry, Multidisciplinary
Angelika Czajkowska, Defne Ilayda Dayi, Helga Weinschrott, Hans-Peter Deigner, Magnus S. Schmidt
Summary: This study examined the competence of amino acids as standards for instrumental biochemical analysis by using benchtop NMR spectrometer and mass spectrometry. It found that stability of amino acid standards varies under different conditions, with some undergoing chemical transformations.
Review
Chemistry, Multidisciplinary
Pallavi Sarkar, Shubhajit Das, Swapan K. Pati
Summary: This article summarizes the progress in the study of non-boron Lewis acids since 2015, which are an important component of Frustrated Lewis pairs.
CHEMISTRY-AN ASIAN JOURNAL
(2022)
Article
Chemistry, Multidisciplinary
Lisanne Sellies, Ruud L. E. G. Aspers, Martin C. Feiters, Floris P. J. T. Rutjes, Marco Tessari
Summary: In recent years, the scope of non-hydrogenative parahydrogen hyperpolarization (nhPHIP) techniques has been expanding, allowing for the detection and quantification of unmodified alpha-amino acids in complex mixtures. This method has shown great potential as demonstrated in human urine samples.
ANGEWANDTE CHEMIE-INTERNATIONAL EDITION
(2021)
