Stereoselective and Stereospecific Triflate Mediated Intramolecular Schmidt Reaction: Easy Access to Alkaloid Skeletons

2020 ◽  
Author(s):  
Lars Gnägi ◽  
Remo Arnold ◽  
Florence Giornal ◽  
Harish Jangra ◽  
Ajoy Kapat ◽  
...  
Keyword(s):  
Theoretical Calculations ◽  
Easy Access ◽  
Chiral Alcohols ◽  
Schmidt Reaction ◽  
Salt Reduction ◽  
Iminium Salt ◽  
Whole Process ◽  
Structural Skeleton

The stereoselectivity and stereospecificity of the triflate mediated intramolecular Schmidt reaction of substituted 3-(1-azidocyclohexyl)propanol derivatives leading to octahydro-1<i>H</i>-pyrrolo[1,2-a]azepine, the structural skeleton of several important families of alkaloids such as the <i>Stemona</i> alkaloids, has been examined. The reaction involves an initial intramolecular S<sub>N</sub>2 reaction between the azide moiety and the triflate affording an intermediate spirocyclic aminodiazonoium salt that undergoes the expected 1,2-shift/N<sub>2</sub>-elimination followed by hydride mediated iminium salt reduction. Remarkably, chiral alcohols are converted to the azabicylic derivative with no or limited racemization. The initial asymmetric alcohol center controls the diastereoselectivity of the whole process leading to the formation of one out of the four possible diastereoisomers of disubstituted octahydro-1<i>H</i>-pyrrolo[1,2-a]azepine. The origin of the stereoselectivity is rationalized based on theoretical calculations. The concise synthesis of (–)-(<i>cis</i>)-3-propylindolizidine and (–)-(<i>cis</i>)-3-butyllehmizidine, two alkaloids found in the venom of workers of the ant <i>Myrmicaria melanogaster</i>, is reported.<br>

scholarly journals Stereochemical Control of the Triflate Mediated Intramolecular Schmidt Reaction

2020 ◽  
Author(s):  
Lars Gnägi ◽  
Florence Giornal ◽  
Harish Jangra ◽  
Ajoy Kapat ◽  
Erich Nyfeler ◽  
...  
Keyword(s):  
Theoretical Calculations ◽  
Chiral Alcohols ◽  
Schmidt Reaction ◽  
Salt Reduction ◽  
Iminium Salt ◽  
Whole Process ◽  
Stereochemical Control ◽  
Structural Skeleton

The stereoselectivity of the triflate mediated intramolecular Schmidt reaction of substituted 3-(1-azidocyclohexyl)propanol derivatives leading to octahydro-1<i>H</i>-pyrrolo[1,2-a]azepine, the structural skeleton of several important families of alkaloids such as the <i>Stemona</i> alkaloids, has been examined. The reaction involves an initial intramolecular S<sub>N</sub>2 reaction between the azide moiety and the triflate affording an intermediate spirocyclic aminodiazonoium salt that undergoes the expected 1,2-shift/N<sub>2</sub>-elimination followed by hydride mediated iminium salt reduction. Remarkably, chiral alcohols are converted to the azabicylic derivative with no or limited racemization. The initial asymmetric alcohol center controls the diastereoselectivity of the whole process leading to the formation of one out of the four possible diastereoisomers of disubstituted octahydro-1<i>H</i>-pyrrolo[1,2-a]azepine. The origin of the stereoselectivity of is rationalized based on theoretical calculations.

scholarly journals Stereochemical Control of the Triflate Mediated Intramolecular Schmidt Reaction

2020 ◽  
Author(s):  
Lars Gnägi ◽  
Florence Giornal ◽  
Harish Jangra ◽  
Ajoy Kapat ◽  
Erich Nyfeler ◽  
...  
Keyword(s):  
Theoretical Calculations ◽  
Chiral Alcohols ◽  
Schmidt Reaction ◽  
Salt Reduction ◽  
Iminium Salt ◽  
Whole Process ◽  
Stereochemical Control ◽  
Structural Skeleton

The stereoselectivity of the triflate mediated intramolecular Schmidt reaction of substituted 3-(1-azidocyclohexyl)propanol derivatives leading to octahydro-1<i>H</i>-pyrrolo[1,2-a]azepine, the structural skeleton of several important families of alkaloids such as the <i>Stemona</i> alkaloids, has been examined. The reaction involves an initial intramolecular S<sub>N</sub>2 reaction between the azide moiety and the triflate affording an intermediate spirocyclic aminodiazonoium salt that undergoes the expected 1,2-shift/N<sub>2</sub>-elimination followed by hydride mediated iminium salt reduction. Remarkably, chiral alcohols are converted to the azabicylic derivative with no or limited racemization. The initial asymmetric alcohol center controls the diastereoselectivity of the whole process leading to the formation of one out of the four possible diastereoisomers of disubstituted octahydro-1<i>H</i>-pyrrolo[1,2-a]azepine. The origin of the stereoselectivity of is rationalized based on theoretical calculations.

scholarly journals Stereoselective and Stereospecific Triflate Mediated Intramolecular Schmidt Reaction: Easy Access to Alkaloid Skeletons

2021 ◽  
Author(s):  
Philippe Renaud ◽  
Lars Gnägi ◽  
Remo Arnold ◽  
Florence Giornal ◽  
Harish Jangra ◽  
...  
Keyword(s):  
Easy Access ◽  
Schmidt Reaction

The interaction of formylporphyrins with weak CH-acids

2003 ◽  
Vol 07 (11) ◽  
pp. 761-765 ◽  
Author(s):  
Yurij V. Ishkov ◽  
Zinaida I. Zhilina ◽  
Ludmila P. Barday
Keyword(s):  
Perchloric Acid ◽  
Condensation Product ◽  
Free Base ◽  
Schmidt Reaction ◽  
Ch Acids ◽  
Iminium Salt

A series of 2(α,β-unsaturated-γ-keto)-5,10,15,20-tetraphenylporphyrins was obtained by condensation of 2-formyl-5,10,15,20-tetraphenylporphyrin with acetone, 1,4-diacetylbenzene, 2-acetylthiophene, acetylacetone and acetophenone according to the Claisen-Schmidt reaction. The condensation product with 1,4-diacetylbenzene could react similarly with another formyl derivative – quinoxalin-6-carboxaldehyde and 2-formyl-5,10,15,20-tetraphenylporphyrin. It is shown that this reaction passes through formation of iminium salt formylporphyrin in presence of free base piperidine and perchloric acid.

XUV Absorption Spectra of Carbon Ions

1988 ◽  
Vol 102 ◽  
pp. 71-73
Author(s):  
E. Jannitti ◽  
P. Nicolosi ◽  
G. Tondello
Keyword(s):  
Absorption Spectra ◽  
Cross Section ◽  
Theoretical Calculations ◽  
Photoionization Cross Section ◽  
Carbon Ions

AbstractThe photoabsorption spectra of the carbon ions have been obtained by using two laser-produced plasmas. The photoionization cross-section of the CV has been absolutely measured and the value at threshold, σ=(4.7±0.5) × 10−19cm2, as well as its behaviour at higher energies agrees quite well with the theoretical calculations.

Relative Intensities in ED Patterns From Thin Gold Films

1972 ◽  
Vol 30 ◽  
pp. 636-637
Author(s):  
R. H. Morriss ◽  
J. D. C. Peng ◽  
C. D. Melvin
Keyword(s):  
Theoretical Calculations ◽  
Diffraction Theory ◽  
Gold Films ◽  
Reasonable Accuracy ◽  
Experimental Conditions ◽  
Crystal Perfection ◽  
Heavy Atoms ◽  
Fine Focus ◽  
Convergent Beam ◽  
Beam Diffraction

Although dynamical diffraction theory was modified for electrons by Bethe in 1928, relatively few calculations have been carried out because of computational difficulties. Even fewer attempts have been made to correlate experimental data with theoretical calculations. The experimental conditions are indeed stringent - not only is a knowledge of crystal perfection, morphology, and orientation necessary, but other factors such as specimen contamination are important and must be carefully controlled. The experimental method of fine-focus convergent-beam electron diffraction has been successfully applied by Goodman and Lehmpfuhl to single crystals of MgO containing light atoms and more recently by Lynch to single crystalline (111) gold films which contain heavy atoms. In both experiments intensity distributions were calculated using the multislice method of n-beam diffraction theory. In order to obtain reasonable accuracy Lynch found it necessary to include 139 beams in the calculations for gold with all but 43 corresponding to beams out of the [111] zone.

Effects of Higher-Order Laue Zone reflections on structure images

1993 ◽  
Vol 51 ◽  
pp. 450-451
Author(s):  
H. S. Kim ◽  
S. S. Sheinin
Keyword(s):  
Wave Vector ◽  
Theoretical Calculations ◽  
Reciprocal Lattice ◽  
Image Plane ◽  
Bloch Wave ◽  
Dynamical Theory ◽  
Higher Order ◽  
Lattice Image ◽  
Lattice Vector ◽  
Image Position

The importance of image simulation in interpreting experimental lattice images is well established. Normally, in carrying out the required theoretical calculations, only zero order Laue zone reflections are taken into account. In this paper we assess the conditions for which this procedure is valid and indicate circumstances in which higher order Laue zone reflections may be important. Our work is based on an analysis of the requirements for obtaining structure images i.e. images directly related to the projected potential. In the considerations to follow, the Bloch wave formulation of the dynamical theory has been used.The intensity in a lattice image can be obtained from the total wave function at the image plane is given by: where ϕg(z) is the diffracted beam amplitide given by In these equations,the z direction is perpendicular to the entrance surface, g is a reciprocal lattice vector, the Cg(i) are Fourier coefficients in the expression for a Bloch wave, b(i), X(i) is the Bloch wave excitation coefficient, ϒ(i)=k(i)-K, k(i) is a Bloch wave vector, K is the electron wave vector after correction for the mean inner potential of the crystal, T(q) and D(q) are the transfer function and damping function respectively, q is a scattering vector and the summation is over i=l,N where N is the number of beams taken into account.

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