Practical Enantioselective Reduction of Ketones Using Oxazaborolidine Catalysts Generated In Situ from Chiral Lactam Alcohols

Kawanami, Yasuhiro; Yanagita, Ryo C.

doi:10.3390/molecules23102408

Cited by 12 publications

(10 citation statements)

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“…In a next step, the mixture of 2c and BH 3 •SMe 2 was heated in situ in the NMR tube at a temperature of 50 • C. The 10 B spectrum (Figure 3c) now shows only one signal at 18.82 ppm that is characteristic of monomeric oxazaborolidine C [10,[72][73][74]. Therefore, we consider this observation as evidence that upon heating of the reaction mixture, the intermediates A and B are subsequently transformed to oxazaborolidine catalyst (C) after evolution of H 2 .…”

Section: Nmr Study Of the Catalytic Systemsmentioning

confidence: 99%

“…Importantly, the 10/11 B spectra are not quantitative, since the relaxation of the quadrupolar B nuclei strongly depends on the symmetry of the boron environment. For example, the relaxation of the boron in structures with higher symmetry such as BH 3 •SMe 2 is generally slower as compared to the relaxation in species with lower symmetry such as A and B.In a next step, the mixture of 2c and BH 3 •SMe 2 was heated in situ in the NMR tube at a temperature of 50 • C. The 10 B spectrum (Figure3c) now shows only one signal at 18.82 ppm that is characteristic of monomeric oxazaborolidine C[10,[72][73][74]. Therefore,…”

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confidence: 99%

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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%

mentioning

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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“…9 In addition, due to the aging of catalysts during storage, CBS catalysts sometimes display low reproducibility. 9c Therefore, the development of more reliable and practical boron-based catalytic protocols remains highly desirable.…”

Section: Boron-based Chiral Organocatalystsmentioning

confidence: 99%

Recent Advances in Organocatalyzed Asymmetric Reduction of Prochiral Ketones: An Update

Qin

Han

2021

Synthesis

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Chiral alcohols are important synthetic intermediates or building blocks for the diverse synthesis of drugs, agrochemicals, and natural products. Asymmetric reduction of prochiral ketones has been the most popularly investigated method for accessing chiral alcohols. In this regard, the organocatalyzed asymmetric reduction as a complementary of transition-metal- and enzyme-catalyzed reactions have attracted tremendous interest in the past decades due to the nature of metal-free and easy operation, as well as, principly, the ease of recovery and reuse of catalysts. Following up a comprehensive overview on organocatalyzed asymmetric reduction of prochiral ketones in early 2018, this short review is intended to summarize the recent progress in this area from the beginning of the year 2018 to the end of Aug. 2021.

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“…Elegant base-mediated strategies require a strong base and a chiral amine catalyst; , the former precludes base-sensitive substrates, and the latter often requires multistep synthesis. The Corey–Bakshi–Shibata reduction also falls short when considering conjugated enones …”

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confidence: 99%

Bimetallic Radical Redox-Relay Catalysis for the Isomerization of Epoxides to Allylic Alcohols

McCallum

Lin

2019

J. Am. Chem. Soc.

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Organic radicals are generally short-lived intermediates with exceptionally high reactivity. Strategically, achieving synthetically useful transformations mediated by organic radicals requires both efficient initiation and selective termination events. Here, we report a new catalytic strategy, namely, bimetallic radical redox-relay, in the regio-and stereoselective rearrangement of epoxides to allylic alcohols. This approach exploits the rich redox chemistry of Ti and Co complexes and merges reductive epoxide ring opening (initiation) with hydrogen atom transfer (termination). Critically, upon effecting key bond-forming and -breaking events, Ti and Co catalysts undergo proton transfer/electron transfer with one another to achieve turnover, thus constituting a truly synergistic dual catalytic system.

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Practical Enantioselective Reduction of Ketones Using Oxazaborolidine Catalysts Generated In Situ from Chiral Lactam Alcohols

Cited by 12 publications

References 42 publications

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

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

Recent Advances in Organocatalyzed Asymmetric Reduction of Prochiral Ketones: An Update

Bimetallic Radical Redox-Relay Catalysis for the Isomerization of Epoxides to Allylic Alcohols

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