Ternary complexes of chiral disulfonimides in transfer-hydrogenation of imines: the relevance of late intermediates in ion pair catalysis

Žabka, Matej; Gschwind, Ruth M.

doi:10.1039/d1sc03724b

Cited by 12 publications

(20 citation statements)

References 57 publications

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“…As can be seen from Scheme , the oxidation potentials of common organic single-electron reductants [ E ox o (XH 2 )] span a very large range about 2.777 V [∼64.0 kcal/mol] from −2.298 V [ E ox o (H • )] to 0.479 V [ E ox o (HEH 2 )] . Since HEH 2 has always been used as a classical electron donor in chemical reactions, especially the photocatalytic reaction, − HEH 2 is assigned as a medium strong electron donor. Compared with common organic single-electron reductants (−2.298 to 0.479 V), all YH – (−0.350 to −0.134 V) with lower oxidation potentials have strong electron-donating abilities, even better than HEH 2 (0.479 V) and BNAH (0.219 V) …”

Section: Resultsmentioning

confidence: 99%

Discovering and Evaluating the Reducing Abilities of Polar Alkanes and Related Family Members as Organic Reductants Using Thermodynamics

Shen

Qian

et al. 2022

J. Org. Chem.

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In this work, the pK a values of 69 polar alkanes (YH 2 ) in acetonitrile were computed using the method developed by Luo and Zhang in 2020, and representative 69 thermodynamic network cards on 22 elementary steps of YH 2 and related polar alkenes (Y) releasing or accepting H 2 were naturally established. Potential electron reductants (YH − ), hydride reductants (YH − ), antioxidants (YH 2 and YH − ), and hydrogen molecule reductants (YH 2 ) are unexpectedly discovered according to thermodynamic network cards. It is also found that there are great differences between YH 2 and common hydrogen molecule reductants (XH 2 ), such as Hantzsch ester (HEH 2 ), benzothiazoline (BTH 2 ), and dihydro-phenanthridine (PH 2 ), releasing two hydrogen ions to unsaturated compounds. During the hydrogenation process, XH 2 release hydrides first, then the oxidation state XH + release protons. However, in the case of YH 2 , YH 2 release protons first, then YH − release hydrides. It is the differences on acidic properties of YH 2 and XH 2 that result in the behavioral and thermodynamic differences on YH 2 and XH 2 releasing two hydrogen ions (H − −H + ). The redox mechanisms and behaviors of Y, YH − , and YH 2 as electron, hydrogen atom, hydride, and hydrogen molecule donors or acceptors in the chemical reaction are reasonably investigated and discussed in this paper using thermodynamics.

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Section: Resultsmentioning

confidence: 99%

Discovering and Evaluating the Reducing Abilities of Polar Alkanes and Related Family Members as Organic Reductants Using Thermodynamics

Shen

Qian

et al. 2022

J. Org. Chem.

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“…Next, we studied the binary complex of CPA and hydrazone by NMR at low temperature. Previously, we were able to obtain structural information about CPA and DSI binary and ternary complexes with imines [32–34] . Thus, we prepared a CPA C1 /( E )‐ 1 a 1 : 1 complex in CD 2 Cl 2 and acquired NMR spectra at 233 K. At this temperature, acid‐promoted isomerization is stopped.…”

Section: Resultsmentioning

confidence: 99%

“…Previously, we were able to obtain structural information about CPA and DSI binary and ternary complexes with imines. [32][33][34] Thus, we prepared a CPA C1/(E)-1 a 1 : 1 complex in CD 2 Cl 2 and acquired NMR spectra at 233 K. At this temperature, acid-promoted isomerization is stopped. Two distinct hydrogen bond signals emerged in a 1 : 1 ratio (δ H 12.87 and 9.60 ppm), corresponding to the two NH sites of the protonated hydrazone.…”

Section: Cyclization Reactionmentioning

confidence: 99%

Substrate Photoswitching for Rate Enhancement of a Organocatalytic Cyclization Reaction

Žabka

Gschwind

2022

Eur J Org Chem

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In this article, we report that applying in situ LED‐NMR irradiation with appropriate wavelength resulted in the photoswitching of an α,β‐unsaturated hydrazone C=N double bond configuration. This reaction was previously reported to be the first step in a chiral Brønsted acid‐catalyzed cyclization reaction, where the minor but stable Z‐isomer is the reactive intermediate. By enhancing the rate of the isomerization, we could show that the overall rate of the cyclization could be increased and followed directly by NMR kinetics. Exclusively light with a specific wavelength matching the isomerization process affected the cyclization. The light‐ and acid‐mediated isomerization provide complementary pathways that can be exploited in synthetic applications to increase reaction rates of asymmetric transformations, especially in reactions requiring high loadings of elaborate chiral catalysts.

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“…Thus far, this report has only focused on the ( Z )-isomer of methylethylideneimine as past studies on reductive amination using organic hydride donors found that the ( Z )-isomer was more kinetically favored than the ( E )-isomer due to a decrease in steric hindrance for the hydride attack. , Our own DFT calculations align with these studies, as it was found that hydride transfer to the ( Z )-isomer of the iminium was slightly kinetically favored by 0.4 kcal/mol over the ( E )-isomer.…”

Section: Resultsmentioning

confidence: 99%

Density Functional Theory Study on the Selective Reductive Amination of Aldehydes and Ketones over Their Reductions to Alcohols Using Sodium Triacetoxyborohydride

Oliphant

Morris

2022

ACS Omega

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Reductive amination is one of the most important methods to synthesize amines, having a wide application in the pharmaceutical, fine chemicals, and materials industries. In general, the reaction begins with dehydration between a carbonyl compound and an amine compound, forming an imine, which is then reduced to an alkylated amine product. Sodium triacetoxyborohydride (STAB) is a popular choice for the reducing agent as it shows selectivity for imines over aldehydes and ketones, which is particularly important in direct reductive amination where the imine and carbonyl compounds are present concurrently. Here, we analyze the reaction pathways of acid-catalyzed direct reductive amination in 1,2-dichloroethane (DCE) with acetaldehyde and methylamine. We find that the transition states for the formation and subsequent reduction of Z -methylethylideneimine (resultant aldimine from acetaldehyde and methylamine) have lower energies than the reduction of acetaldehyde. Transition state structures for the hydride transfers are organized by the Lewis-acidic sodium ion. Additionally, reduction reactions with formaldehyde and acetone and their imine derivatives (with methylamine) are investigated, and again, the hydride transfer to the resultant aldimine or ketimine is lower in energy than that of their parent carbonyl compound.

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Ternary complexes of chiral disulfonimides in transfer-hydrogenation of imines: the relevance of late intermediates in ion pair catalysis

Abstract: In ion pairing catalysis, the structures of advanced intermediates are often not accessible. Here, we present a combined experimental and computational study of ternary complexes in Brønsted acid catalysis, which show unexpected H-bond switching.

Cited by 12 publications

References 57 publications

Discovering and Evaluating the Reducing Abilities of Polar Alkanes and Related Family Members as Organic Reductants Using Thermodynamics

Discovering and Evaluating the Reducing Abilities of Polar Alkanes and Related Family Members as Organic Reductants Using Thermodynamics

Substrate Photoswitching for Rate Enhancement of a Organocatalytic Cyclization Reaction

Density Functional Theory Study on the Selective Reductive Amination of Aldehydes and Ketones over Their Reductions to Alcohols Using Sodium Triacetoxyborohydride

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