Structure assignment of aminoconduritols by 15N NMR correlation spectroscopy; synthesis of a positional isomer of 7-deoxypancratistatin

2001 ◽  
Vol 79 (11) ◽  
pp. 1659-1667 ◽  
Author(s):  
Stefan Schilling ◽  
Uwe Rinner ◽  
Collin Chan ◽  
Ion Ghiviriga ◽  
Tomas Hudlicky
Keyword(s):  
Nmr Spectroscopy ◽  
Lewis Acid ◽  
Positional Isomer ◽  
Correlation Spectroscopy ◽  
15N Nmr ◽  
Early Stages ◽  
12 Steps ◽  
Nmr Techniques ◽  
Acid Catalyzed ◽  
Structure Assignment

A positional isomer of 7-deoxypancratistatin was synthesized in 12 steps from epoxyaziridines 4 and 5. An intermolecular opening of the aziridine rather than the epoxide in the early stages of the synthesis led to 13, which did not match the properties of tetraacetate 10 derived from 7-deoxypancratistatin. At no stage of the synthesis did standard NMR techniques, involving 1H–1H or 1H–13C coupling, prove adequate for the structure assignment. Unambiguous structure was assigned by 1H–15N correlation NMR spectroscopy as well as by the conversion of epoxide 11 to diol 29 synthesized independently by another route. Experimental and spectral details are reported for all new compounds.Key words: 15N NMR spectroscopy, iso-7-deoxypancratistatin, Lewis acid catalyzed intramolecuar opening of epoxides, aminoconduritols.

Recent advances in the application of 13C and 15N NMR spectroscopy to soil organic matter studies

Soil Research ◽  
2000 ◽  
Vol 38 (4) ◽  
pp. 769 ◽  
Author(s):  
N. J. Mathers ◽  
X. A. Mao ◽  
P. G. Saffigna ◽  
Z. H. Xu ◽  
S. J. Berners-Price ◽  
...  
Keyword(s):  
Organic Matter ◽  
Nmr Spectroscopy ◽  
Soil Organic Matter ◽  
Environmental Science ◽  
Soil Extract ◽  
15N Nmr ◽  
Particle Size Fractionation ◽  
15N Nmr Spectroscopy ◽  
Nmr Techniques ◽  
Pre Treatment

Nuclear magnetic resonance (NMR) spectroscopy has been applied to many studies in soil science, geochemistry, and environmental science. In recent years, the study of soil organic matter (SOM) using NMR techniques has progressed rapidly. NMR spectroscopy has been used to study chemical changes of SOM during decomposition, and also of soil extract fractions such as humic acid and fulvic acid. NMR spectroscopy of soils has improved rapidly in recent years with the introduction of pre-treatment and particle-size fractionation. In addition to routine liquid- and solid-state 13C NMR applications, 15N NMR spectra of natural abundant samples have been reported, but 15N-enriched material is more convenient to use due to the low natural abundance of 15N. Some newly developed NMR techniques have also been utilised, such as 2-dimensional NMR spectroscopy and improved 1H NMR techniques. These are reviewed and commented on in this paper.

Catalytic Carbonyl-Olefin Metathesis of Aliphatic Ketones: Iron(III) HomoDimers as Lewis Acidic Superelectrophiles

2018 ◽  
Author(s):  
Haley Albright ◽  
Paul S. Riehl ◽  
Christopher C. McAtee ◽  
Jolene P. Reid ◽  
Jacob R. Ludwig ◽  
...  
Keyword(s):  
Lewis Acid ◽  
Olefin Metathesis ◽  
Acid Activation ◽  
Lewis Acid Catalysts ◽  
Distinct Mode ◽  
Aliphatic Ketones ◽  
Carbon Carbon Bond ◽  
Metathesis Reactions ◽  
Acid Catalyzed

<div>Catalytic carbonyl-olefin metathesis reactions have recently been developed as a powerful tool for carbon-carbon bond</div><div>formation. However, currently available synthetic protocols rely exclusively on aryl ketone substrates while the corresponding aliphatic analogs remain elusive. We herein report the development of Lewis acid-catalyzed carbonyl-olefin ring-closing metathesis reactions for aliphatic ketones. Mechanistic investigations are consistent with a distinct mode of activation relying on the in situ formation of a homobimetallic singly-bridged iron(III)-dimer as the active catalytic species. These “superelectrophiles” function as more powerful Lewis acid catalysts that form upon association of individual iron(III)-monomers. While this mode of Lewis acid activation has previously been postulated to exist, it has not yet been applied in a catalytic setting. The insights presented are expected to enable further advancement in Lewis acid catalysis by building upon the activation principle of “superelectrophiles” and broaden the current scope of catalytic carbonyl-olefin metathesis reactions.</div>

Synthesis of cyano(selenone)gold(I) complexes and investigation of their scrambling reactions using 13C and 15N NMR spectroscopy

Polyhedron ◽  
2002 ◽  
Vol 21 (21) ◽  
pp. 2099-2105 ◽  
Author(s):  
Saeed Ahmad ◽  
Anvarhusein A. Isab ◽  
Abdul Rahman Al-Arfaj ◽  
Alan P. Arnold
Keyword(s):  
Nmr Spectroscopy ◽  
15N Nmr ◽  
15N Nmr Spectroscopy

scholarly journals Comparison of Corn Stover Pretreatments with Lewis Acid Catalyzed Choline Chloride, Glycerol and Choline Chloride-Glycerol Deep Eutectic Solvent

Polymers ◽  
2021 ◽  
Vol 13 (7) ◽  
pp. 1170
Author(s):  
Yuan Zhu ◽  
Benkun Qi ◽  
Xinquan Liang ◽  
Jianquan Luo ◽  
Yinhua Wan
Keyword(s):  
Corn Stover ◽  
Lewis Acid ◽  
Choline Chloride ◽  
Deep Eutectic Solvent ◽  
Enzymatic Saccharification ◽  
Glycerol Solution ◽  
Cellulose Conversion ◽  
Biomass Processing ◽  
Acid Catalyzed ◽  
Highly Correlated

Herein, corn stover (CS) was pretreated by less corrosive lewis acid FeCl3 acidified solutions of neat and aqueous deep eutectic solvent (DES), aqueous ChCl and glycerol at 120 °C for 4 h with single FeCl3 pretreatment as control. It was unexpected that acidified solutions of both ChCl and glycerol were found to be more efficient at removing lignin and xylan, leading to higher enzymatic digestibility of pretreated CS than acidified DES. Comparatively, acidified ChCl solution exhibited better pretreatment performance than acidified glycerol solution. In addition, 20 wt% water in DES dramatically reduced the capability of DES for delignification and xylan removal and subsequent enzymatic cellulose saccharification of pretreated CS. Correlation analysis showed that enzymatic saccharification of pretreated CS was highly correlated to delignification and cellulose crystallinity, but lowly correlated to xylan removal. Recyclability experiments of different acidified pretreatment solutions showed progressive decrease in the pretreatment performance with increasing recycling runs. After four cycles, the smallest decrease in enzymatic cellulose conversion (22.07%) was observed from acidified neat DES pretreatment, while the largest decrease (43.80%) was from acidified ChCl pretreatment. Those findings would provide useful information for biomass processing with ChCl, glycerol and ChCl-glycerol DES.

scholarly journals Metal-Free Catalysts for the Polymerization of Alkynyl-Based Monomers

Catalysts ◽  
2020 ◽  
Vol 11 (1) ◽  
pp. 1 ◽  
Author(s):  
Jie Zhang ◽  
Zhiming Zhang ◽  
Fulin Yang ◽  
Haoke Zhang ◽  
Jingzhi Sun ◽  
...  
Keyword(s):  
Lewis Acid ◽  
Research Focus ◽  
Catalytic Systems ◽  
Metal Free ◽  
Catalyst Free ◽  
Material Sciences ◽  
Acid Catalyzed

Novel polymerizations based on alkyne monomers are becoming a powerful tool to construct polymers with unique structures and advanced functions in the areas of polymer and material sciences, and scientists have been attracted to develop a variety of novel polymerizations in recent decades. Therein, catalytic systems play an indispensable role in the influence of polymerization efficiencies and the performances of the resultant polymers. Concerning the shortcomings of metallic catalysts, much of the recent research focus has been on metal-free polymerization systems. In this paper, metal-free catalysts are classified and the corresponding polymerizations are reviewed, including organobase-catalyzed polymerizations, Lewis-acid-catalyzed polymerizations, as well as catalyst-free polymerizations. Moreover, the challenges and perspectives in this area are also briefly discussed.

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