Unconventional Bifunctional Lewis-Brønsted Acid Activation Mode in Bicyclic Guanidine-Catalyzed Conjugate  Addition Reactions

Cho, Bokun; Wong, Ming Wah

doi:10.3390/molecules200815108

Cited by 13 publications

(12 citation statements)

References 40 publications

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“…The proton affinity of the N2 atom (226.4 kcal·mol −1 ) is higher than those of N3 (196.3 kcal·mol −1 ) and N5 (199.6 kcal·mol −1 ). This indicated that the N2 atom with strong basicity [ 38 , 39 , 40 , 41 , 42 , 43 , 49 ] could work as the reacting site for the deprotonation of CH 3 NO 2 in the Henry reaction.…”

Section: Resultsmentioning

confidence: 99%

“…It can abstract a proton from the substrate and catalyze the reaction as its conjugated acid (i.e., the guanidinium cation). A bifunctional Brønsted acid activation mode has been proposed, in which the electrophile and nucleophile are positioned by a guanidinium cation via hydrogen bonding [ 38 , 39 , 40 , 41 , 42 , 43 ]. In 2015, Feng and Liu [ 44 ] developed an open-chain guanidine–amide organocatalyst for asymmetric aza-Henry reactions of isatin-derived N -Boc ketimines.…”

Section: Introductionmentioning

confidence: 99%

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Guanidine–Amide-Catalyzed Aza-Henry Reaction of Isatin-Derived Ketimines: Origin of Selectivity and New Catalyst Design

Tang

et al. 2021

Molecules

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Density functional theory (DFT) calculations were performed to investigate the mechanism and the enantioselectivity of the aza-Henry reaction of isatin-derived ketimine catalyzed by chiral guanidine–amide catalysts at the M06-2X-D3/6-311+G(d,p)//M06-2X-D3/6-31G(d,p) (toluene, SMD) theoretical level. The catalytic reaction occurred via a three-step mechanism: (i) the deprotonation of nitromethane by a chiral guanidine–amide catalyst; (ii) formation of C–C bonds; (iii) H-transfer from guanidine to ketimine, accompanied with the regeneration of the catalyst. A dual activation model was proposed, in which the protonated guanidine activated the nitronate, and the amide moiety simultaneously interacted with the ketimine substrate by intermolecular hydrogen bonding. The repulsion of CPh3 group in guanidine as well as N-Boc group in ketimine raised the Pauli repulsion energy (∆EPauli) and the strain energy (∆Estrain) of reacting species in the unfavorable si-face pathway, contributing to a high level of stereoselectivity. A new catalyst with cyclopropenimine and 1,2-diphenylethylcarbamoyl as well as sulfonamide substituent was designed. The strong basicity of cyclopropenimine moiety accelerated the activation of CH3NO2 by decreasing the energy barrier in the deprotonation step. The repulsion between the N-Boc group in ketimine and cyclohexyl group as well as chiral backbone in the new catalyst raised the energy barrier in C–C bond formation along the si-face attack pathway, leading to the formation of R-configuration product. A possible synthetic route for the new catalyst is also suggested.

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Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Guanidine–Amide-Catalyzed Aza-Henry Reaction of Isatin-Derived Ketimines: Origin of Selectivity and New Catalyst Design

Tang

et al. 2021

Molecules

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“…Equation 5 below depicts the dissociation of GuI to its conjugate acid and base pair. 484 The guanidinium ion (Gu + ) can donate a H + in a reaction 485,486 (discussed later in chapter 7.6), meanwhile the Icontributes an electron to reduce a thiophene molecule as seen for Iodine doping on polyaniline. [487][488][489][490][491] Equation 6 depicts the proposed equation for the redox reaction.…”

Section: Proposed Mechanisms For Increased Seebeck Coefficientmentioning

confidence: 99%

“…This gives further evidence the dissociated guanidinium ions underwent redox reactions. 486 In the desulphonation mechanism (Figure 7.6.3.2) the electron rich 𝜋𝜋 electrons of benzenesulfonic acid attacks the electron deficient H from the N + in a nucleophilic elimination reaction whereby SO3 is the elimination product and H + added onto the benzene ring to replace it. 584,585 The now basic guanidine and guanidinium (source of H + ) is involved in a further reaction whereby it guanidine reduces the S03 group into SH2 (refer to Equation 6) .…”

Section: P a G Ementioning

confidence: 99%

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Improvement to the thermoelectric properties of PEDOT:PSS

Atoyo¹

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Thermoelectric materials can convert waste heat to electricity without moving parts. Extensive research into improving the efficiency of inorganic thermoelectric materials has allowed some materials such as bismuth tellurides to be commercialized. These materials, however, contain materials in low abundance on earth such as tellurium therefore their use and scaled production would be limited. Organic and hybrid thermoelectric materials can meet the gap for niche markets as well as be synthesized on mass, due to utilization of earth abundant elements such as carbon, sulphur, and nitrogen. The thermoelectric generators require several n and p-type materials connected for optimal efficiency. There are many ways to create inorganic thermoelectric n and p-types. However, for the organic thermoelectric materials the efficiency lags because of their lower electrical conductivity and Seebeck coefficient as well as the lack of effective strategies in the development of n-type materials. Poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) is one of the most successful and researched p-type organic thermoelectric material and thus, the thesis will explore effective strategies for decoupling the apparent trade-offs observed when improving either the electrical conductivity or Seebeck coefficient. The first major contribution to knowledge discussed in this study is the utilization of a reducing agent treatment on PEDOT-ionic liquid composites (reader is advised to refer to chapter 5). Another significant finding was the successful development of a novel route to an n-type single walled carbon nanotube, PEDOT:PSS composite (please refer to chapter 6). The final and most significant contribution to knowledge in this research project was the development of a set of novel single walled carbon nanotube, ionic liquid, PEDOT:PSS composites whereby after a post treatment with a guanidinium iodide in ethylene glycol solution allowed for improvement of the electrical conductivity from 3.4 S cm -1 to 3665 S cm-1 and Seebeck coefficient from 12 μV K-1 to 27 μV K-1 thereby leading to an optimised power factor of 236 μW m-1 K-1 at 140 °C (please refer to chapter 7).

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Addition Reactions: Polar Additions

Knipe¹

2019

Organic Reaction Mechanisms Series

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Unconventional Bifunctional Lewis-Brønsted Acid Activation Mode in Bicyclic Guanidine-Catalyzed Conjugate Addition Reactions

Cited by 13 publications

References 40 publications

Guanidine–Amide-Catalyzed Aza-Henry Reaction of Isatin-Derived Ketimines: Origin of Selectivity and New Catalyst Design

Guanidine–Amide-Catalyzed Aza-Henry Reaction of Isatin-Derived Ketimines: Origin of Selectivity and New Catalyst Design

Improvement to the thermoelectric properties of PEDOT:PSS

Addition Reactions: Polar Additions

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