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1. On the relevance of glycosyl oxonium ions to 1,2- cis -selective O -glycosylation in ether solvents

   https://doi.org/10.1080/07328303.2024.2410800  

   Agarkar, Varad; Hart, Ava E; Ragains, Justin R (November 2024, Journal of Carbohydrate Chemistry)

   Since no later than the 1970s, organic chemists have speculated on the role of glycosyl oxonium ions in chemical O-glycosylation. Such species result from the attack of ethers on glycosyl oxocarbenium ions and are invoked to explain 1,2-cis-selectivity in ether solvents. However, a systematic study to probe this phenomenon appears to be lacking in the chemical literature. Herein, we study the effects of solvent, counteranion, protecting group electron-withdrawing effects, and acceptor on O-glycosylation stereoselectivity with D-glucosyl trichloroacetimidate donors. While many of these transformations proceed with 1,2- cis-selectivity, our results suggest that glycosyl oxonium ions play minimal, if any, role in O-glycosylation. 

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2. Why is thiol unexpectedly less reactive but more selective than alcohol in phenanthroline-catalyzed 1,2- cis O - and S -furanosylations?

   https://doi.org/10.1039/d4ob01593b  

   Ramakrishna, Boddu S; Rani, Neha; Xu, Hengfu; Alan-Lee, Cyrus; Schlegel, H Bernhard; Nguyen, Hien M (January 2025, Organic & Biomolecular Chemistry)

   The lack of catalytic stereoselective approaches for producing 1,2-cis S-furanosides emphasizes the critical need for further research in this area. Herein, we present a stereoselective S-furanosylation method, utilizing a 4,7-dipiperidine-substituted phenanthroline catalyst. This developed protocol fills a gap in the field, enabling the coupling of cysteine residues and thiols with furanosyl bromide electrophiles. The process allows for stereoselective access to 1,2-cis S-furanosides. Through computational and experimental investigations, thiol is found to be less reactive than alcohol but exhibits greater stereoselectivity. The 1,2-cis stereoselectivity of O-products depends on the nature of the electrophile, while S-products are obtained with excellent 1,2-cis stereoselectivity, irrespective of the furanose structure. The displaced bromide ion from the glycosyl electrophile influences the reaction’s reactivity and stereoselectivity. Alcohol-OH forms a stronger hydrogen bond with bromide ion than thiol-SH, contributing to the difference in their reactivity. The energy difference between forming S-furanoside and O-furanoside transition states is 3.7 kcal/mol, supporting the increased reactivity of alcohol over thiol. The difference in transition state energies between the major and minor S-product is greater than that for the major and minor O-product. This is consistent with experimental data showing how thiol is more stereoselective than alcohol. The catalyst and reaction conditions utilized for the generation of 1,2-cis O-furanosides in our prior studies are found to be unsuitable for the synthesis of 1,2-cis S-furanosides. In the present study, a highly reactive phenanthroline catalyst and specific reaction conditions have been developed to achieve stereoselective S-linked product formation. 

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3. C∙∙∙O and Si∙∙∙O Tetrel Bonds: Substituent Effects and Transfer of the SiF3 Group

   https://doi.org/10.3390/ijms241511884  

   Niu, Zhihao; Wu, Qiaozhuo; Li, Qingzhong; Scheiner, Steve (August 2023, International Journal of Molecular Sciences)

   The tetrel bond (TB) between 1,2-benzisothiazol-3-one-2-TF3-1,1-dioxide (T = C, Si) and the O atom of pyridine-1-oxide (PO) and its derivatives (PO-X, X = H, NO2, CN, F, CH3, OH, OCH3, NH2, and Li) is examined by quantum chemical means. The Si∙∙∙O TB is quite strong, with interaction energies approaching a maximum of nearly 70 kcal/mol, while the C∙∙∙O TB is an order of magnitude weaker, with interaction energies between 2.0 and 2.6 kcal/mol. An electron-withdrawing substituent on the Lewis base weakens this TB, while an electron-donating group has the opposite effect. The SiF3 group transfers roughly halfway between the N of the acid and the O of the base without the aid of cooperative effects from a third entity. 

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4. Calcium‐Ion Binding Mediates the Reversible Interconversion of Cis and Trans Peroxido Dicopper Cores

   https://doi.org/10.1002/anie.202105421  

   Vargo, Natasha P.; Harland, Jill B.; Musselman, Bradley W.; Lehnert, Nicolai; Ertem, Mehmed Z.; Robinson, Jerome R. (July 2021, Angewandte Chemie International Edition)

   Abstract Coupled dinuclear copper oxygen cores (Cu₂O₂) featured in type III copper proteins (hemocyanin, tyrosinase, catechol oxidase) are vital for O₂transport and substrate oxidation in many organisms.μ‐1,2‐cisperoxido dicopper cores (^CP) have been proposed as key structures in the early stages of O₂binding in these proteins; their reversible isomerization to other Cu₂O₂cores are directly relevant to enzyme function. Despite the relevance of such species to type III copper proteins and the broader interest in the properties and reactivity of bimetallic^CPcores in biological and synthetic systems, the properties and reactivity of^CPCu₂O₂species remain largely unexplored. Herein, we report the reversible interconversion ofμ‐1,2‐transperoxido (^TP) and^CPdicopper cores. Ca^IImediates this process by reversible binding at the Cu₂O₂core, highlighting the unique capability for metal‐ion binding events to stabilize novel reactive fragments and control O₂activation in biomimetic systems. 

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5. Catalytic Stereoselective 1,2- cis -Furanosylations Enabled by Enynal-Derived Copper Carbenes

   https://doi.org/10.1021/acscatal.3c05237  

   Ghosh, Bidhan; Alber, Adam; Lander, Chance W; Shao, Yihan; Nicholas, Kenneth M; Sharma, Indrajeet (January 2024, ACS Catalysis)

   Chang, Sukbok (Ed.)

   1,2-cis-Furanosides are present in various biomedically relevant glycosides, and their stereoselective synthesis remains a significant challenge. In this vein, we have developed a stereoselective approach to 1,2-cis-furanosylations using earth-abundant copper catalysis. This protocol proceeds under mild conditions at room temperature and employs readily accessible benchtop stable enynalderived furanose donors. This chemistry accommodates a variety of alcohols, including primary, secondary, and tertiary, as well as mannosyl alcohol acceptors, which have been incompatible with most known methods of furanosylation. The resulting 1,2-cisfuranoside products exhibit high yields and anomeric selectivity with both the ribose and arabinose series. Furthermore, the anomeric selectivity is independent of the C2 oxygen-protecting group and the anomeric configuration of the starting donor. Experimental evidence and computational studies support our hypothesis that copper chelation between the C2 oxygen of the furanose donor and an incoming alcohol nucleophile is responsible for the observed 1,2-cisstereoselectivity. 

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