Chiral Aminoalcohols and Squaric Acid Amides as Ligands for Asymmetric Borane Reduction of Ketones: Insight to In Situ Formed Catalytic System by DOSY and Multinuclear NMR Experiments

A series of squaric acid amides (synthesized in 66–99% isolated yields) and a set of chiral aminoalcohols were comparatively studied as ligands in a model reaction of reduction of α-chloroacetophenone with BH<sub>3</sub>•SMe<sub>2</sub>. In all cases, the aminoalcohols demons...

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Autores principales:	Yana Nikolova, Georgi M. Dobrikov, Zhanina Petkova, Pavletta Shestakova
Formato:	article
Lenguaje:	EN
Publicado:	MDPI AG 2021
Materias:	asymmetric reduction borane complexes chiral aminoalcohols DOSY NMR squaramides Organic chemistry QD241-441
Acceso en línea:	https://doaj.org/article/ad7341feec5148f6891c12d37280b2a9
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spelling	oai:doaj.org-article:ad7341feec5148f6891c12d37280b2a92021-11-25T18:27:56ZChiral Aminoalcohols and Squaric Acid Amides as Ligands for Asymmetric Borane Reduction of Ketones: Insight to In Situ Formed Catalytic System by DOSY and Multinuclear NMR Experiments10.3390/molecules262268651420-3049https://doaj.org/article/ad7341feec5148f6891c12d37280b2a92021-11-01T00:00:00Zhttps://www.mdpi.com/1420-3049/26/22/6865https://doaj.org/toc/1420-3049A series of squaric acid amides (synthesized in 66–99% isolated yields) and a set of chiral aminoalcohols were comparatively studied as ligands in a model reaction of reduction of α-chloroacetophenone with BH<sub>3</sub>•SMe<sub>2</sub>. In all cases, the aminoalcohols demonstrated better efficiency (up to 94% <i>ee</i>), while only poor asymmetric induction was achieved with the corresponding squaramides. A mechanistic insight on the in situ formation and stability at room temperature of intermediates generated from ligands and borane as possible precursors of the oxazaborolidine-based catalytic system has been obtained by <sup>1</sup>H DOSY and multinuclear 1D and 2D (<sup>1</sup>H, <sup>10/11</sup>B, <sup>13</sup>C, <sup>15</sup>N) NMR spectroscopy of equimolar mixtures of borane and selected ligands. These results contribute to better understanding the complexity of the processes occurring in the reaction mixture prior to the possible oxazaborolidine formation, which play a crucial role on the degree of enantioselectivity achieved in the borane reduction of α-chloroacetophenone.Yana NikolovaGeorgi M. DobrikovZhanina PetkovaPavletta ShestakovaMDPI AGarticleasymmetric reductionborane complexeschiral aminoalcoholsDOSY NMRsquaramidesOrganic chemistryQD241-441ENMolecules, Vol 26, Iss 6865, p 6865 (2021)
institution	DOAJ
collection	DOAJ
language	EN
topic	asymmetric reduction borane complexes chiral aminoalcohols DOSY NMR squaramides Organic chemistry QD241-441
spellingShingle	asymmetric reduction borane complexes chiral aminoalcohols DOSY NMR squaramides Organic chemistry QD241-441 Yana Nikolova Georgi M. Dobrikov Zhanina Petkova Pavletta Shestakova Chiral Aminoalcohols and Squaric Acid Amides as Ligands for Asymmetric Borane Reduction of Ketones: Insight to In Situ Formed Catalytic System by DOSY and Multinuclear NMR Experiments
description	A series of squaric acid amides (synthesized in 66–99% isolated yields) and a set of chiral aminoalcohols were comparatively studied as ligands in a model reaction of reduction of α-chloroacetophenone with BH<sub>3</sub>•SMe<sub>2</sub>. In all cases, the aminoalcohols demonstrated better efficiency (up to 94% <i>ee</i>), while only poor asymmetric induction was achieved with the corresponding squaramides. A mechanistic insight on the in situ formation and stability at room temperature of intermediates generated from ligands and borane as possible precursors of the oxazaborolidine-based catalytic system has been obtained by <sup>1</sup>H DOSY and multinuclear 1D and 2D (<sup>1</sup>H, <sup>10/11</sup>B, <sup>13</sup>C, <sup>15</sup>N) NMR spectroscopy of equimolar mixtures of borane and selected ligands. These results contribute to better understanding the complexity of the processes occurring in the reaction mixture prior to the possible oxazaborolidine formation, which play a crucial role on the degree of enantioselectivity achieved in the borane reduction of α-chloroacetophenone.
format	article
author	Yana Nikolova Georgi M. Dobrikov Zhanina Petkova Pavletta Shestakova
author_facet	Yana Nikolova Georgi M. Dobrikov Zhanina Petkova Pavletta Shestakova
author_sort	Yana Nikolova
title	Chiral Aminoalcohols and Squaric Acid Amides as Ligands for Asymmetric Borane Reduction of Ketones: Insight to In Situ Formed Catalytic System by DOSY and Multinuclear NMR Experiments
title_short	Chiral Aminoalcohols and Squaric Acid Amides as Ligands for Asymmetric Borane Reduction of Ketones: Insight to In Situ Formed Catalytic System by DOSY and Multinuclear NMR Experiments
title_full	Chiral Aminoalcohols and Squaric Acid Amides as Ligands for Asymmetric Borane Reduction of Ketones: Insight to In Situ Formed Catalytic System by DOSY and Multinuclear NMR Experiments
title_fullStr	Chiral Aminoalcohols and Squaric Acid Amides as Ligands for Asymmetric Borane Reduction of Ketones: Insight to In Situ Formed Catalytic System by DOSY and Multinuclear NMR Experiments
title_full_unstemmed	Chiral Aminoalcohols and Squaric Acid Amides as Ligands for Asymmetric Borane Reduction of Ketones: Insight to In Situ Formed Catalytic System by DOSY and Multinuclear NMR Experiments
title_sort	chiral aminoalcohols and squaric acid amides as ligands for asymmetric borane reduction of ketones: insight to in situ formed catalytic system by dosy and multinuclear nmr experiments
publisher	MDPI AG
publishDate	2021
url	https://doaj.org/article/ad7341feec5148f6891c12d37280b2a9
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_version_	1718411151831728128

Chiral Aminoalcohols and Squaric Acid Amides as Ligands for Asymmetric Borane Reduction of Ketones: Insight to In Situ Formed Catalytic System by DOSY and Multinuclear NMR Experiments

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