Evidence against reversible Wittig reaction of a stabilized ylide: high (E)-olefin selectivity under kinetic control

1987 ◽  
Vol 52 (20) ◽  
pp. 4637-4639 ◽  
Author(s):  
E. Vedejs ◽  
T. Fleck ◽  
S. Hara
Keyword(s):  
Wittig Reaction ◽  
Kinetic Control ◽  
Olefin Selectivity

ChemInform Abstract: Evidence Against Reversible Wittig Reaction of a Stabilized Ylide: High E-Olefin Selectivity Under Kinetic Control.

ChemInform ◽  
1988 ◽  
Vol 19 (11) ◽  
Author(s):  
E. VEDEJS ◽  
T. FLECK ◽  
S. HARA
Keyword(s):  
Wittig Reaction ◽  
Kinetic Control ◽  
Olefin Selectivity

The synthesis, isomerization and stability of some enol-lactones

1982 ◽  
Vol 35 (9) ◽  
pp. 1903 ◽  
Author(s):  
IR Doyle ◽  
RA Massy-Westropp
Keyword(s):  
Thermal Decomposition ◽  
Wittig Reaction ◽  
Alder Reaction ◽  
Diels Alder ◽  
Kinetic Control ◽  
Relative Stabilities ◽  
Diels Alder Reaction ◽  
Wittig Reactions

The photoisomerization of enol-lactones is described. Thermal decomposition of (E) and (Z) ethyl 3-oxo-1,3,3aβ,4α,7α,7aβ-hexahydro-4,7-methanoisobenzofran-1-yideneacetates provides a good route to (E) and (Z) ethyl 5-oxo-2,5-dihydrofuran-2-ylideneacetates. Other examples of this retro-Diels-Alder reaction are reported. The relative stabilities of (E) and (Z) enol-lactones from the Wittig reaction between substituted succinic anhydrides and ethoxycarbonylmethylenetriphenylphosphorane have been determined. These Wittig reactions are under kinetic control.

Aspects of the mechanism of the Wittig reaction between cyclic anhydrides and stabilized phosphoranes

1982 ◽  
Vol 35 (10) ◽  
pp. 2077 ◽  
Author(s):  
AD Abell ◽  
RA Massy-Westropp
Keyword(s):  
Intermediate Product ◽  
Wittig Reaction ◽  
Product Formation ◽  
Initial Reaction ◽  
Kinetic Control ◽  
Cyclic Anhydrides ◽  
Influence Of Substituents ◽  
Phthalic Anhydrides

It has been established that the Wittig reaction between cyclic anhydrides and methoxycarbonylmethylenetriphenylphosphorane, a reaction used for the preparation of enol-lactones, proceeds via an acyclic intermediate acylated phosphorane for the three classes of anhydrides studied: succinic, maleic and phthalic. The formation of the acyclic intermediate can be irreversible or reversible, depending on the structure of the anhydride. The stereochemistry of the enol-lactones produced is not controlled by the initial reaction of the anhydride with the ylide but either during or after cyclization of the acyclic intermediate. Product formation appears to be under kinetic control with all the anhydrides studied. The influence of substituents in substituted phthalic anhydrides has been investigated.

Double Ring-Closing Approach for the Synthesis of 2,3,6,7-Substituted Anthracene Derivatives

2020 ◽  
Author(s):  
Birgit Meindl ◽  
Katharina Pfennigbauer ◽  
Berthold Stöger ◽  
Martin Heeney ◽  
Florian Glöcklhofer
Keyword(s):  
Wittig Reaction ◽  
Condensation Reaction ◽  
Synthetic Methods ◽  
Anthracene Derivative ◽  
Double Ring ◽  
Mild Conditions ◽  
Wide Range ◽  
Anthracene Derivatives

Anthracene derivatives have been used for a wide range of applications and many different synthetic methods for their preparation have been developed. However, despite continued synthetic efforts, introducing substituents in some positions has remained difficult. Here we present a method for the synthesis of 2,3,6,7-substituted anthracene derivatives, one of the most challenging anthracene substitution patterns to obtain. The method is exemplified by the preparation of 2,3,6,7-anthracenetetracarbonitrile and employs a newly developed, stable protected 1,2,4,5-benzenetetracarbaldehyde as the precursor. The precursor can be obtained in two scalable synthetic steps from 2,5-dibromoterephthalaldehyde and is converted into the anthracene derivative by a double intermolecular Wittig reaction under very mild conditions followed by a deprotection and intramolecular double ring-closing condensation reaction. Further modification of the precursor is expected to enable the introduction of additional substituents in other positions and may even enable the synthesis of fully substituted anthracene derivatives by the presented approach.<br>

Revisiting Wittig Olefination and Aza-Wittig Reaction for Carbohydrate Transformations and Stereocontrol in Sugar Chemistry

2014 ◽  
Vol 18 (13) ◽  
pp. 1731-1748 ◽  
Author(s):  
Vasco Cachatra ◽  
Amelia Rauter
Keyword(s):  
Wittig Reaction ◽  
Sugar Chemistry ◽  
Wittig Olefination

Computational Study on the Kinetics and Mechanisms of Unimolecular Reactions of (Z)-(Z)-N-(λ5-phosphanylidene) Formohydrazonic Formic Anhydride: Intramolecular aza-Wittig Reaction in Competition with Mumm Rearrangement

2020 ◽  
Vol 17 (11) ◽  
pp. 884-889
Author(s):  
Somayeh Mirdoraghi ◽  
Hamed Douroudgari ◽  
Farideh Piri ◽  
Morteza Vahedpour
Keyword(s):  
Rate Constants ◽  
Density Functional ◽  
Wittig Reaction ◽  
Computational Study ◽  
Single Step ◽  
Low Energy ◽  
Coupled Cluster ◽  
Unimolecular Reaction ◽  
Single Step Reaction ◽  
Good Agreement

For (Z)-(Z)-N-(λ5-phosphanylidene) formohydrazonic formic anhydride, Aza-Wittig reaction and Mumm rearrangement are studied using both density functional and coupled cluster theories. For this purpose, two different products starting from one substrate are considered that are competing with each other. The obtained products, P1 and P2, are thermodynamically favorable. The product of the aza-Wittig reaction, P1, is more stable than the product of Mumm rearrangement (P2). For the mentioned products, just one reliable pathway is separately proposed based on unimolecular reaction. Therefore, the rate constants based on RRKM theory in 300-600 K temperature range are calculated. Results show that the P1 generation pathway is a suitable path due to low energy barriers than the path P2. The first path has three steps with three transition states, TS1, TS2, and TS3. The P2 production path is a single-step reaction. In CCSD level, the computed barrier energies are 14.55, 2.196, and 10.67 kcal/mol for Aza-Wittig reaction and 42.41 kcal/mol for Mumm rearrangement in comparison with the corresponding complexes or reactants. For final products, the results of the computational study are in a good agreement with experimental predictions.

Trypsin entrapped within liposomes. Partition of a low-molecular-mass substrate as the main factor in kinetic control of hydrolysis

1991 ◽  
Vol 56 (3) ◽  
pp. 712-717 ◽  
Author(s):  
Jana Formelová ◽  
Albert Breier ◽  
Peter Gemeiner ◽  
Lubica Kurillová
Keyword(s):  
Molecular Mass ◽  
Egg Yolk ◽  
Kinetic Control ◽  
Hydrolysis Kinetics ◽  
Liposomal Membrane ◽  
Kinetics Of ◽  
Main Factor

Trypsin has been entrapped within liposomes prepared from egg yolk phospholipides by the method of controlled dialysis, and the hydrolysis kinetics of Nα-benzoyl-DL-arginine p-nitroaniline catalyzed by the liposome-entrapped trypsin has been studied by monitoring the flux of substrate and product across the liposomal membrane. The partitioning of the substrate and product between liposomal and extraliposomal environment has been found to represent the main factor in the kinetic control of the hydrolysis.

Kinetic Control of Length and Morphology of Segmented Polymeric Nanofibers in Microfluidic Chips

Langmuir ◽  
2020 ◽  
Vol 36 (44) ◽  
pp. 13364-13370
Author(s):  
Zhengping Tan ◽  
Zaiyan Hou ◽  
Ke Wang ◽  
Yuce Li ◽  
Lianbin Zhang ◽  
...  
Keyword(s):  
Kinetic Control ◽  
Microfluidic Chips ◽  
Polymeric Nanofibers

scholarly journals Near quantitative synthesis of urea macrocycles enabled by bulky N-substituent

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Yingfeng Yang ◽  
Hanze Ying ◽  
Zhixia Li ◽  
Jiang Wang ◽  
Yingying Chen ◽  
...  
Keyword(s):  
High Efficiency ◽  
Molecular Structures ◽  
High Yield ◽  
Kinetic Control ◽  
High Concentration ◽  
Weak Association ◽  
Quantitative Synthesis ◽  
Thermodynamic Stabilization ◽  
Discrete Structures ◽  
Very High

AbstractMacrocycles are unique molecular structures extensively used in the design of catalysts, therapeutics and supramolecular assemblies. Among all reactions reported to date, systems that can produce macrocycles in high yield under high reaction concentrations are rare. Here we report the use of dynamic hindered urea bond (HUB) for the construction of urea macrocycles with very high efficiency. Mixing of equal molar diisocyanate and hindered diamine leads to formation of macrocycles with discrete structures in nearly quantitative yields under high concentration of reactants. The bulky N-tert-butyl plays key roles to facilitate the formation of macrocycles, providing not only the kinetic control due to the formation of the cyclization-promoting cis C = O/tert-butyl conformation, but also possibly the thermodynamic stabilization of macrocycles with weak association interactions. The bulky N-tert-butyl can be readily removed by acid to eliminate the dynamicity of HUB and stabilize the macrocycle structures.

scholarly journals Tackling Pristinamycin IIB Problems: Synthetic Studies toward Some Fluorinated Analogs

2020 ◽  
Vol 3 (1) ◽  
pp. 107
Author(s):  
Assia Chebieb ◽  
Chewki Ziani-Cherif
Keyword(s):  
Chemical Structure ◽  
Wittig Reaction ◽  
Antimicrobial Agents ◽  
Synthetic Approach ◽  
Solubility In Water ◽  
Fluorinated Analogs ◽  
Human Therapy ◽  
Primary Structures ◽  
Synthetic Studies

Streptogramins are potent antibiotics against numerous highly resistant pathogens and therefore are used in last-resort human therapy. These antibiotics are formed of both A- and B-group compounds named pristinamycins that differ in their basic primary structures. Although pristinamycin IIB is among the most interesting antibiotics in this family, it presents numerous problems related to its chemical structure, such as instability at most pH levels, weak solubility in water, and resistance by bacteria. As a response to the need for developing new antimicrobial agents, we have designed a new analog of pristinamycin IIB, based most importantly on the introduction of fluorine atoms. We conjectured indeed that the introduced modifications may solve the above-mentioned problems exhibited by pristinamycin IIB. Our multistep synthetic approach relies on few key reactions, namely a Wittig reaction, a Grubbs reaction, and dihydroxy, -difluoro API (Advanced Pharmaceutical Intermediate) synthesis

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