Publications by authors named "Krista Gulbe"

2 Publications

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Metal-free glycosylation with glycosyl fluorides in liquid SO.

Beilstein J Org Chem 2021 29;17:964-976. Epub 2021 Apr 29.

Institute of Technology of Organic Chemistry, Faculty of Materials Science and Applied Chemistry, Riga Technical University, P. Valdena str. 3, Riga, LV-1048, Latvia.

Liquid SO is a polar solvent that dissolves both covalent and ionic compounds. Sulfur dioxide possesses also Lewis acid properties, including the ability to covalently bind Lewis basic fluoride ions in a relatively stable fluorosulfite anion (FSO). Herein we report the application of liquid SO as a promoting solvent for glycosylation with glycosyl fluorides without any external additive. By using various temperature regimes, the method is applied for both armed and disarmed glucose and mannose-derived glycosyl fluorides in moderate to excellent yields. A series of pivaloyl-protected - and -mannosides, as well as one example of a -mannoside, are synthesized to demonstrate the scope of the glycosyl acceptors. The formation of the fluorosulfite species during the glycosylation with glycosyl fluorides in liquid SO is proved by F NMR spectroscopy. A sulfur dioxide-assisted glycosylation mechanism that proceeds via solvent separated ion pairs is proposed, whereas the observed α,β-selectivity is substrate-controlled and depends on the thermodynamic equilibrium.
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http://dx.doi.org/10.3762/bjoc.17.78DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8093551PMC
April 2021

Synthesis of Sulfones Ru(II)-Catalyzed Sulfination of Boronic Acids.

J Org Chem 2020 Apr 31;85(8):5660-5669. Epub 2020 Mar 31.

Institute of Technology of Organic Chemistry, Faculty of Materials Science and Applied Chemistry, Riga Technical University, P. Valdena Street 3, Riga, LV-1048, Latvia.

Ruthenium(II) complexes catalyze the insertion of sulfur dioxide into (het)aryl and alkenyl boronic acids. The transmetalation-sulfination process proceeds with DABSO in the presence of 5 mol % RuCl(PPh) in methanol at 100 °C. The intermediate sulfinate salt can be quenched with various electrophiles such as alkyl halides, epoxides, Michael acceptors, and λ-iodanes in moderate to good yields. The reported sulfone synthesis can be performed either as a direct one-pot or one-pot two-step procedure depending on the reactivity of the electrophile.
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http://dx.doi.org/10.1021/acs.joc.9b03403DOI Listing
April 2020