Lewis Base‐Catalyzed, Lewis Acid‐Mediated Reactions (<scp>n</scp>?→?σ*)

Rossi, Sergio; Denmark, Scott E.

doi:10.1002/9783527675142.ch21

Cited by 7 publications

(9 citation statements)

References 77 publications

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“…Inspired by previously reported examples, we decided to start our investigation by employing the phthalic acid primary diamide moiety as a recognition system [ 17 , 18 , 19 ]. Binaphthyl diamine-derived phosphoramide was selected as the catalytic center, since this type of structure has proven to be an efficient organocatalyst in many type of reactions involving the generation of hypervalent trichlorosilyl species [ 1 , 2 ]. As the Lewis base and the self-assembly recognition system are fixed, the subsequent step consisted of the evaluation of the correct linker between these two functionalities.…”

Section: Resultsmentioning

confidence: 99%

“…29 Si spectra showed two signals only: −19 ppm, due to free SiCl 4 and one at −46 ppm, corresponding to a tetravalent silicon atom bounded with oxygen atoms. No signals were observed in the range from −200 to −210 ppm, expected for hexacoordinated silicon species [ 2 , 33 , 34 ]. Moreover, raising the temperature from −50 °C to RT, it was possible to observe a partial degradation of the ligand 7c corresponding to the elimination of 4- n Bu-aniline 10 with consequent formation of a phthalimide derivative 9 .…”

Section: Resultsmentioning

confidence: 99%

“…The most important examples of mono- and bis-phosphoroamides used in stereoselective processes were developed by Denmark [ 1 ]. These compounds have found extensive application as catalysts in the so called “Lewis base-catalyzed Lewis acid-mediated reactions” [ 2 ] where the combination of chlorosilanes with enantiomerically pure phosphoroamides or phosphinoxides [ 3 ] leads to an in situ formation of a new hypervalent (cationic) silicon species with increased acidity at the silicon center that acts as chiral Lewis acid and efficiently promotes highly stereoselective reactions ( Figure 1 ) [ 4 , 5 , 6 ].…”

Section: Introductionmentioning

confidence: 99%

“…C 2 symmetric bis-phosphoroamides have been preferentially used, due to the possibility of generating a highly defined space around the silicon atom that can better guarantee high stereocontrol. The conformational restriction provided by the linkage, if well optimized, favorably influences the selectivity and the activity of the catalyst [ 2 , 7 ]. Generally, the structure of these bisdentate phosphoroamides presents two distinct Lewis basic moieties connected through a covalent achiral linker, and their synthesis requires a long and not trivial sequence of synthetic steps.…”

Section: Introductionmentioning

confidence: 99%

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Novel Chiral Bis-Phosphoramides as Organocatalysts for Tetrachlorosilane-Mediated Reactions

et al. 2017

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The formation of novel chiral bidentate phosphoroamides structures able to promote Lewis base-catalyzed Lewis acid-mediated reactions was investigated. Two different classes of phosphoroamides were synthetized: the first class presents a phthalic acid/primary diamine moiety, designed with the aim to perform a self-assembly recognition process through hydrogen bonds; the second one is characterized by the presence of two phosphoroamides as side arms connected to a central pyridine unit, able to chelate SiCl4 in a 2:1 adduct. These species were tested as organocatalysts in the stereoselective allylation of benzaldehyde and a few other aromatic aldehydes with allyl tributyltin in the presence of SiCl4 with good results. NMR studies confirm that only pyridine-based phosphoroamides effectively coordinate tetrachlorosilane and may lead to the generation of a self-assembled entity that would act as a promoter of the reaction. Although further work is necessary to clarify and confirm the formation of the hypothesized adduct, the study lays the foundation for the design and the synthesis of chiral supramolecular organocatalysts.

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Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Novel Chiral Bis-Phosphoramides as Organocatalysts for Tetrachlorosilane-Mediated Reactions

et al. 2017

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“…In particular, the Sakurai-Hosomi-Denmark allylation reaction (Scheme 1) is commonly used for the development of new chiral Lewis bases. Significant experimental contributions in this field include the work of Denmark, Kočovský, Malkov, Nakajima, and more recently from one of us [4][5][6][7][8][9][10][11]. The stereochemical aspects of these reactions have been initially rationalized using conventional stereoelectronic arguments for the transition states (TSs) of the transient hypervalent silicon intermediates [12].…”

Section: Introductionmentioning

confidence: 99%

Steps toward Rationalization of the Enantiomeric Excess of the Sakurai–Hosomi–Denmark Allylation Catalyzed by Biisoquinoline N,N’-Dioxides Using Computations

et al. 2021

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Allylation reactions of aldehydes are chemical transformations of fundamental interest, as they give direct access to chiral homoallylic alcohols. In this work, we focus on the full computational characterization of the catalytic activity of substituted biisoquinoline-N,N’-dioxides for the allylation of 2-naphthaldehyde. We characterized the structure of all transition states as well as identified the π stacking interactions that are responsible for their relative energies. Motivated by disagreement with the experimental results, we also performed an assessment of 34 different density functional methods, with the goal of assessing DFT as a general tool for understanding this chemistry. We found that the DFT results are generally consistent as long as functionals that correctly account for dispersion interactions are used. However, agreement with the experimental results is not always guaranteed. We suggest the need for a careful synergy between computations and experiments to correctly interpret the data and use them as a design tool for new and improved asymmetric catalysts.

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Chelation Equilibria and π-Electron Delocalization in Neutral Hypercoordinate Organosilicon Complexes of Pyrithione

et al. 2022

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A series of neutral pyrithionato (OPTO) organosilicon compounds, R 3 Si(OPTO) [R = Me (1), Ph (2)], cis-R 2 Si(OPTO) 2 [R = Me (3), Et (4), i Pr (5), t Bu (6), mesityl (10), allyl (11), p-tolyl (13); R 2 = (CH 2 ) 3 ( 7), (CH 2 ) 4 ( 8), (CH 2 ) 5 (9), Me, allyl (12)], and cis-R 2 Si(OPTO)Cl [R = Me (14), i Pr (15), allyl ( 16), p-tolyl (17), mesityl (18), Ph (19)], have been prepared and characterized by 1 H, 13 C, and 29 Si NMR spectroscopy. X-ray crystallographic analysis reveals four-coordinate silicon atoms in 1, 2, 6, and 10, five-coordinate in 3, 9, 11, 12, and 14−19, six-coordinate in 7 and 8, and primarily six-coordinate with cocrystallized five-coordinate forms in 13. Collectively, a wide range of chelate strengths of the OPTO ligand is observed in these complexes characterized by the Si−S bond length and S−Si−O bite angle in the solid state, which correlates well with the solutionstate 13 C NMR C�S chemical shift. In TBP five-coordinate silicon complexes, the ambidentate potential of the OPTO ligand and πelectron delocalization (π-ED) that occurs within the ligand generally allows the chelate effect to be enhanced with sulfur occupying an equatorial vs axial position. For 8, 9, and 18, reversible chelation equilibria involving Si ← S bond formation and concurrent π-ED have been characterized by variable-temperature 13 C and 29 Si NMR spectroscopy. Solvents of varying dielectric constants were found to have pronounced effects on the 13 C NMR chemical shifts of 1, 15, and pyrithione.

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Lewis Base‐Catalyzed, Lewis Acid‐Mediated Reactions (n?→?σ*)

Cited by 7 publications

References 77 publications

Novel Chiral Bis-Phosphoramides as Organocatalysts for Tetrachlorosilane-Mediated Reactions

Novel Chiral Bis-Phosphoramides as Organocatalysts for Tetrachlorosilane-Mediated Reactions

Steps toward Rationalization of the Enantiomeric Excess of the Sakurai–Hosomi–Denmark Allylation Catalyzed by Biisoquinoline N,N’-Dioxides Using Computations

Chelation Equilibria and π-Electron Delocalization in Neutral Hypercoordinate Organosilicon Complexes of Pyrithione

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