scholarly journals The Bull–James assembly as a chiral auxiliary and shift reagent in kinetic resolution of alkyne amines by the CuAAC reaction

2016 ◽  
Vol 14 (46) ◽  
pp. 10778-10782 ◽  
Author(s):  
William D. G. Brittain ◽  
Brette M. Chapin ◽  
Wenlei Zhai ◽  
Vincent M. Lynch ◽  
Benjamin R. Buckley ◽  
...  
Keyword(s):  
Nmr Spectroscopy ◽  
Boronic Acid ◽  
Kinetic Resolution ◽  
Enantiomeric Excess ◽  
Shift Reagent ◽  
Chiral Auxiliary ◽  
H Nmr ◽  
Chiral Shift Reagent ◽  
Cuaac Reaction

The Bull–James boronic acid assembly is used simultaneously as a chiral auxiliary for kinetic resolution and as a chiral shift reagent for in situ enantiomeric excess (ee) determination by 1H NMR spectroscopy.

An improved chiroporphyrin shift reagent for the enantiomeric assay of amino acid derivatives by 1H NMR spectroscopy: evaluation of iodorhodium(III) tetramethylchiroporphyrin

2002 ◽  
Vol 06 (06) ◽  
pp. 396-402 ◽  
Author(s):  
Magalie Claeys-Bruno ◽  
Jacques Pécaut ◽  
Michel Bardet ◽  
Jean-Claude Marchon
Keyword(s):  
Amino Acid ◽  
Nmr Spectroscopy ◽  
Kinetic Resolution ◽  
Dimethyl Ester ◽  
Spectroscopic Studies ◽  
Shift Reagent ◽  
Strong Impact ◽  
H Nmr ◽  
Derivatizing Agent ◽  
Amino Acid Mixtures

1 H NMR spectroscopic studies of amino ester complexation indicate that iodorhodium(III) tetramethylchiroporphyrin RhI(TMCP) has a single axial site available for the coordination of amine groups, and that it retains its iodo ligand trans to the coordinated amine. This conclusion is confirmed by the X-ray structure of the 1:1 adduct of n-propylamine with RhI(TMCP). This stoichiometry of amine binding makes RhI(TMCP) a superior chiral derivatizing agent relative to CoCl ( TMCP ), which gives 1:2 adducts. It may have a strong impact in the utilization of RhI(TMCP) for the enantiomeric assay of amino acid mixtures by 1 H NMR spectroscopy. Axial exchange of the (R)- and (S)-enantiomers of aspartic acid dimethyl ester on RhI(TMCP) is moderately slow, and equilibrium is reached in a few minutes without kinetic resolution.

Revisiting the iridacycle-catalyzed hydrosilylation of enolizable imines

2018 ◽  
Vol 8 (24) ◽  
pp. 6316-6329
Author(s):  
Jorge Pèrez-Miqueo ◽  
Virginia San Nacianceno ◽  
F. Borja Urquiola ◽  
Zoraida Freixa
Keyword(s):  
Nmr Spectroscopy ◽  
H Nmr

In situ1H NMR spectroscopy reveals a cascade mechanism for the hydrosilylation of enolizable imines catalyzed by iridium(iii) metallacycles.

A new chiral shift reagent for the determination of enantiomeric excess and absolute configuration in cyanohydrins

2009 ◽  
pp. 1067 ◽  
Author(s):  
Lomary S. Moon ◽  
Ravinder S. Jolly ◽  
Yoganjaneyulu Kasetti ◽  
Prasad V. Bharatam
Keyword(s):  
Absolute Configuration ◽  
Enantiomeric Excess ◽  
Shift Reagent ◽  
Chiral Shift Reagent

scholarly journals On-Demand Release of Secondary Amine Bases for the Activation of Catalysts and Crosslinkers

2021 ◽  
Author(s):  
Benjamin Spitzbarth ◽  
Rienk Eelkema
Keyword(s):  
Nmr Spectroscopy ◽  
Secondary Amine ◽  
Self Healing ◽  
Polymer Gel ◽  
Free Base ◽  
H Nmr ◽  
On Demand ◽  
Water Shift ◽  
Reaction Cascades

We demonstrate that the species present in the equilibrium of DCv ureas can be employed in reaction cascades and as triggered organocatalysts. Easily controllable stimuli like heat or addition of water shift the equilibrium towards isocyanate and free base which can function as an in situ released reagent, both catalytically and in an equimolar fashion in different reactions. While applying heat to the system leads to a reversible liberation of amine base, addition of water makes this release irreversible. We demonstrate this application of DCv ureas with two examples via <sup>1</sup>H-NMR spectroscopy. Firstly, we use the liberated base to activate a protected organocatalyst for acylhydrazone formation. Secondly, this base can be employed to trigger the release of nitrile-N-oxides from chlorooximes, which can react with 4-arm PEG-thiols to form a thiohydroximate polymer gel. These findings show the utility of DCv hindered ureas beyond their application in self-healing.

scholarly journals Living β-selective cyclopolymerization using Ru dithiolate catalysts

2019 ◽  
Vol 10 (39) ◽  
pp. 8955-8963 ◽  
Author(s):  
Kijung Jung ◽  
Tonia S. Ahmed ◽  
Jaeho Lee ◽  
Jong-Chan Sung ◽  
Hyeyun Keum ◽  
...  
Keyword(s):  
Nmr Spectroscopy ◽  
Kinetic Studies ◽  
Steric Factor ◽  
Rational Engineering ◽  
H Nmr ◽  
Mechanistic Investigation

Herein, we demonstrate the first example of living β-selective CP by rational engineering of the steric factor on monomer or catalyst structures, along with a mechanistic investigation by in situ kinetic studies using 1H NMR spectroscopy.

Enantioselective Michael Addition: An Experimental Introduction to Asymmetric Synthesis

2019 ◽  
Author(s):  
Martin Tiano
Keyword(s):  
Undergraduate Students ◽  
Michael Addition ◽  
Enantiomeric Excess ◽  
Diethyl Malonate ◽  
2D Nmr ◽  
Shift Reagent ◽  
Experimental Session ◽  
H Nmr ◽  
Asymmetric Michael Addition ◽  
Chiral Lewis Acid

<p> We adapted a classical asymmetric Michael addition for a 1-day experimental session (6-8 hrs) for third or fourth-year undergraduate students. The experiment follows up three steps : synthesis of a chiral Lewis Acid, LiAl(BINOL)<sub>2</sub>, then its use as a catalyst in the Michael addition of diethyl malonate on cyclopentenone, followed by purification through column chromatography on silica gel. The desired product can be fully characterized by 1D and 2D NMR experiments and IR spectroscopy. The enantiomeric excess can be determined by polarimetry and <sup>1</sup>H NMR using chiral lanthanide shift reagent Eu(hfc)<sub>3</sub>.</p>

In situ reactions with trichloroacetyl isocyanate and their application to structural assignment of hydroxy compounds by 1H NMR spectroscopy. A general comment

1979 ◽  
Vol 44 (2) ◽  
pp. 558-588 ◽  
Author(s):  
Zdeněk Samek ◽  
Miloš Buděšínský
Keyword(s):  
Nmr Spectroscopy ◽  
Structural Analysis ◽  
Functional Groups ◽  
1H Nmr Spectroscopy ◽  
H Nmr ◽  
Structural Assignment ◽  
Trichloroacetyl Isocyanate ◽  
In Situ Reactions ◽  
Hydroxy Compounds

The application possibilities of the in situ reactions of trichloroacetyl isocyanate (TAI method) to structural assignment of alcohols by means of 1H NMR spectroscopy are critically evaluated. The possibilities of TAI acylations in various solvents are demonstrated and the reactivity of various functional groups, potentially complicating or extending the applications of TAI, is discussed. In addition to their use in structural analysis such reactions also can serve as model experiments for preparative purposes.

In situ reactions of amines and amino alcohols and their application to structural assignment by 1H NMR spectroscopy

1980 ◽  
Vol 45 (10) ◽  
pp. 2784-2803 ◽  
Author(s):  
Miloš Buděšínský ◽  
Zdeněk Samek ◽  
Miloš Tichý
Keyword(s):  
Nmr Spectroscopy ◽  
Structural Analysis ◽  
1H Nmr Spectroscopy ◽  
Amino Alcohols ◽  
Sample Tube ◽  
H Nmr ◽  
Structural Assignment ◽  
Trichloroacetyl Isocyanate ◽  
In Situ Reactions

The in situ reaction of amines with trichloroacetyl isocyanate (TAI) in the NMR sample tube was investigated as a tool in structural analysis by means of 1H NMR spectroscopy. Preferred conformations of the adducts were suggested which explain different behaviour of NH protons and the induced CH protons shifts. On the example of amino alcohols it was shown how to use the TAI method in combination with other in situ reactions (protonation, acetylation, trifluoroacetylation) for simultaneous differentiation between functional groups in polyfunctional molecules.

In situ preparation of cyclopropanones with the bicyclo[3.1.0]hexan-6-one skeleton (substituted examples of the Loftfield intermediate). Confirmation of a very facile intramolecular alkyl cyclopropanone – dienol rearrangement

1996 ◽  
Vol 74 (1) ◽  
pp. 79-87 ◽  
Author(s):  
T. S. Sorensen ◽  
F. Sun
Keyword(s):  
Nmr Spectroscopy ◽  
Sigmatropic Rearrangement ◽  
Unsaturated Ketone ◽  
Tert Butyl ◽  
H Nmr ◽  
In Situ Preparation ◽  
Rate Determining Step ◽  
Enol Formation ◽  
C Nmr

Four substituted bicyclo[3.1.0]hexan-6-ones (cyclopropanones) were prepared in situ, starting from the corresponding 2,6-dibromocyclohexanone and reductively removing the bromine atoms with the organometallic salt PPN+Cr(CO)4NO− The reaction is essentially instantaneous at −78 or−100 °C, and can be conveniently carried out in an NMR tube for easy characterization of the products by low-temperature 1H and 13C NMR spectroscopy. The1,5-di-tert-butyl and 1-tert-butyl analogs were thermally stable to ca. 0 °C, but the 1-tert-butyl-5-methyl and 1-tert-butyl-5-ethyl derivatives were extremely labile, rearranging at ca. −80 °C into a cross-conjugated enol, where the methyl (or ethyl) substituent was converted into an exomethylene group. These enols were also characterized as in situ species using 1H and 13C NMR spectroscopy, and by allowing the enol → α,β-unsaturated ketone rearrangement to take place at about 25 °C. The mechanism of the enol formation was investigated using a 1 -tert-butyl-5-CD3 analog, and the kH/kD ratio for enol formation was determined to be 6 ± 2. From this, the rate-determining step in the enol formation was postulated as a C-H → H-O transfer of a hydrogen atom in a cyclohexyl oxyallyl intermediate. The 1,5-di-tert-butylbicyclohexanone shows dynamic 1H NMR line broadening, the origin of which is also proposed to involve a cyclohexyl oxyallyl intermediate. Key words: cyclopropanone, oxyallyl, bicyclo[3.1.0]hexan-6-one, dienol, sigmatropic rearrangement.

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