Studies on the synthesis of borazines from borane and 1,2-aminoalcohols

Stepanenko, Viatcheslav; Ortiz-Marciales, Margarita; Barnes, C. E.; García, Carmina Saldaña

doi:10.1016/j.tetlet.2006.08.071

Cited by 15 publications

(18 citation statements)

References 36 publications

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“…With the aim to better understand the reasons behind the significantly lower enantioselectivity obtained using chiral squaric acid derivatives as ligands compared to the corresponding free chiral aminoalcohols, more detailed studies were performed. According to literature data, different reactive intermediates, as well as monomeric and dimeric oxazaborolidine species, may exist in dynamic equilibrium in the reaction mixture depending on the ligand structure and concentration, type of the solvent and borane reagent [61][62][63][64][65][66][67]. The possible presence of these equilibrating species in situ is a key feature of the catalyst system influencing its performance and activity.…”

Section: Nmr Study Of the Catalytic Systemsmentioning

confidence: 99%

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

et al. 2021

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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 BH3•SMe2. In all cases, the aminoalcohols demonstrated better efficiency (up to 94% ee), 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 1H DOSY and multinuclear 1D and 2D (1H, 10/11B, 13C, 15N) 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.

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Section: Nmr Study Of the Catalytic Systemsmentioning

confidence: 99%

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

et al. 2021

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“…An attempted isolation by removal of volatiles with heating, results in the formation borazine 2, which is a much less active and selective catalyst compared to 1 (eq 4). 9 The B-alkyl derivatives of 1 can be readily prepared by its reaction with alkyllithium, followed by treatment with solid ammonium chloride (eq 5). 10 The polymer-linked B-aryl-substituted ent-1 has been prepared by the reaction of (1S,2R)-norephedrine with phenylboronic acid linked to the styrene/bromostyrene copolymer.…”

Section: Marek Zaidlewicz and Marek Krzeminski Nicolaus Copernicus Univmentioning

confidence: 99%

Norephedrine-Borane

Poli

Zaidlewicz

Krzemiński

2014

Encyclopedia of Reagents for Organic Synthesis

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“…Commonly employed B − H oxazaborolidines are prepared by the in situ addition of a chiral amino alcohol with an excess of borane, without isolation and characterization of the catalyst precursor. A recent study [99] has shown that polycyclic borazines are frequently formed via this method and could account for some of the unwanted side -products and low enantioselectivities sometimes observed in the catalyzed reactions. Indeed, borane was found to react initially with norephedrine at 0 ° C to give the expected N -borane adduct, as shown by multinuclear NMR spectroscopy.…”

Section: Catalyzed Reactionsmentioning

confidence: 99%