Green chemistry
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Arylboronates are helpful building blocks in organic synthesis. Here, we present an efficient mechanochemical synthesis of arylboronates from arene diazonium salts. Importantly, this transformation was significantly enhanced by sodium chloride, which probably promotes the decomposition of diazonium salts via anion exchange. Chloride anions also participate in the formation of strongly reducing Cl−B anion radical intermediate that promotes radical chain reaction. The reaction proceeds more efficiently with a small amount of polar solvent as a liquid-assisted grinding additive. Quantum chemical calculations support the mechanistic proposal.
Mechanochemical Radical Boronation of Aryl Diazonium Salts Promoted by Sodium Chloride. S. Andrejčák, P. Kisszékelyi, M. Májek, R. Šebesta, Eur. J. Org. Chem. 2023, e202201399. DOI: https://doi.org/10.1002/ejoc.202201399
Mechanochemical Radical Boronation of Aryl Diazonium Salts Promoted by Sodium Chloride. S. Andrejčák, P. Kisszékelyi, M. Májek, R. Šebesta, Eur. J. Org. Chem. 2023, e202201399. DOI: https://doi.org/10.1002/ejoc.202201399
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Chiral heterocycles occur in many compounds of interest, but their efficient synthesis is challenging. This study concerns the enantioselective and diastereoselective synthesis of densely substituted chiral pyran derivatives. Diastereodivergence of the oxa-Diels-Alder reaction is achieved by using either a bifunctional amino-thiourea or a monofunctional quinine organocatalyst under ball-milling conditions. Liquid-assisted grinding proves a highly efficient means of affording pyrans in high yield, with high enantiomeric purities and short reaction times.
T. Peňaška, V. Modrocká, K. Stankovianska, M. Mečiarová, E. Rakovský, R. Šebesta, ChemSusChem 2022, e202200028.
DOI: 10.1002/cssc.202200028.
T. Peňaška, V. Modrocká, K. Stankovianska, M. Mečiarová, E. Rakovský, R. Šebesta, ChemSusChem 2022, e202200028.
DOI: 10.1002/cssc.202200028.
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Mechanochemical activation effectively mediated asymmetric organocatalytic domino Mannich addition followed by diastereoselective fluorination. The Mannich reactions of pyrazolones and to a lesser extent those of isoxazolones were effective under solvent-free ball-milling conditions. This reaction in combination with a chiral squaramide catalyst provided corresponding products in high yields and enantiomeric purities up to 99:1 e.r. and as a single diastereomer. DFT calculations revealed reasons for high diastereoselectivity.
D. Krištofíková, M. Mečiarová, E. Rakovský, R. Šebesta, ACS Sust. Chem. Eng. 2020, 8, 14417–14424.
DOI: https://doi.org/10.1021/acssuschemeng.0c04260
D. Krištofíková, M. Mečiarová, E. Rakovský, R. Šebesta, ACS Sust. Chem. Eng. 2020, 8, 14417–14424.
DOI: https://doi.org/10.1021/acssuschemeng.0c04260
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Rapid improvements: Asymmetric organocatalysis can be efficiently combined with various green chemistry methodologies. Acceleration techniques, such as ball milling, flow, high pressure, or light, offer higher yields, faster reactions, easier product isolation, and new reactivities. More sustainable reaction media, such as ionic liquids, deep eutectic solvents, green solvent alternatives, and water, also improve the sustainability profile of organocatalytic reactions.
D. Krištofíková, V. Modrocká, M. Mečiarová, R. Šebesta, ChemSusChem 2020, 13, 2828-2858.
DOI: https://doi.org/10.1002/cssc.202000137
D. Krištofíková, V. Modrocká, M. Mečiarová, R. Šebesta, ChemSusChem 2020, 13, 2828-2858.
DOI: https://doi.org/10.1002/cssc.202000137
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Application of aqueous media and solvent-free conditions have been assessed for asymmetric organocatalytic α-aminoxylation and hydrazination of aldehydes. Both sets of conditions considerably sped up these reactions, while keeping high enantioselectivity.
E. Veverková, V. Modrocká, R Šebesta, Eur. J. Org. Chem. 2017, 1191-1195; DOI: 10.1002/ejoc.201601357.
E. Veverková, V. Modrocká, R Šebesta, Eur. J. Org. Chem. 2017, 1191-1195; DOI: 10.1002/ejoc.201601357.