[2,3]-Sigmatropic rearrangement of an in situ prepared ylide and a thio ether to thio ester conversion as key steps in short syntheses of sarkomycin and its phenyl thio ester

1985 ◽  
Vol 50 (16) ◽  
pp. 2965-2968 ◽  
Author(s):  
Theodore Cohen ◽  
Zenyk Kosarych ◽  
Kunio Suzuki ◽  
Lin Chen Yu
Keyword(s):  
Sigmatropic Rearrangement ◽  
Key Steps

scholarly journals Methionine-stabilized nonclassical growth within self-assembled de novo gold nanoparticles in conjunction with secondary nucleation inhibition

2021 ◽  
Author(s):  
Jitendra Sahu ◽  
Shahbaz Lone ◽  
Kalyan Sadhu
Keyword(s):  
Self Assembly ◽  
De Novo ◽  
Noble Metal Nanoparticles ◽  
Secondary Nucleation ◽  
Unique Case ◽  
Primary Particles ◽  
Growth Reaction ◽  
Aurophilic Interaction ◽  
Key Steps

Abstract The key steps for seed mediated growth of noble metal nanoparticles involve primary and secondary nucleation, which depends upon the energy barrier and ligand supersaturation standards of the medium. Herein we report the unique case of methionine (Met) controlled growth reaction, which rather proceeds via impeding secondary nucleation in presence of citrate stabilized gold nanoparticle (AuNP). The interaction between freshly generated Au+ and thioether group of Met in the medium restricts the secondary nucleation process involving further Au+ reduction. This incomplete conversion of Au+ results in a significant enhancement of the zeta (ζ) potential even at low concentration of Met. Furthermore, the aurophilic interaction of Au+ controls the self-assembly process of the in situ generated emissive nucleated particles. Nucleation of primary particles on seed surface, their segregation and time dependent conversion to larger particles within self-assembly confirm the nonclassical growth, which has further been explored with Met containing bio-inspired peptides.

scholarly journals Vanadium-catalyzed selenide oxidation with in situ [2,3] sigmatropic rearrangement (SOS reaction): scope and asymmetric applications

2004 ◽  
Vol 2 (9) ◽  
pp. 1315-1329 ◽  
Author(s):  
T. Campbell Bourland ◽  
Rich G. Carter ◽  
Alexandre F. T. Yokochi
Keyword(s):  
Sigmatropic Rearrangement

Acylation of Nitronates: [3,3]-Sigmatropic Rearrangement of in Situ Generated N-Acyloxy,N-oxyenamines

2018 ◽  
Vol 83 (18) ◽  
pp. 11057-11066 ◽  
Author(s):  
Aleksandr O. Kokuev ◽  
Yulia A. Antonova ◽  
Valentin S. Dorokhov ◽  
Ivan S. Golovanov ◽  
Yulia V. Nelyubina ◽  
...  
Keyword(s):  
Sigmatropic Rearrangement

scholarly journals The Tidal Stream Energy Resource of the Fromveur Strait—A Review

2020 ◽  
Vol 8 (12) ◽  
pp. 1037
Author(s):  
Nicolas Guillou ◽  
Jean-Frédéric Charpentier ◽  
Mohamed Benbouzid
Keyword(s):  
Energy Resource ◽  
Tidal Energy ◽  
Energy Output ◽  
Wake Interactions ◽  
Tidal Stream ◽  
Technical Specifications ◽  
Tidal Stream Energy ◽  
Key Steps ◽  
A Site

Refined assessments of the available tidal stream energy resource are required to optimize turbines design and guarantee successful implementations and operations of devices in the marine environment. Investigations primary focused on identifying areas with maximum current speeds. However, further information may be reached by exhibiting (i) resource temporal variability, (ii) superimposed effects of meteo-oceanographic conditions (including especially wind-generated surface-gravity waves), and (iii) potential environmental impacts of operating turbines at the regional (e.g., changes in sediment transport and surrounding seabed features, effects on marine water quality, etc.) and local (wake-wake interactions and energy output) scales. These aspects are here investigated by reviewing a series of research studies dedicated to the Fromveur Strait off western Brittany, a region with strong potential for tidal array development along the coast of France. Particular attention is dedicated to the exploitation of combined in-situ and remote-sensing observations and numerical simulations. Beyond a site specific characterization of the tidal stream energy resource, this review promotes a series of original approaches and analysis methods for turbines optimization, thus complementing technical specifications to secure the key steps of a tidal energy project and promote the growth of a reliable tidal stream energy exploitation.

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.

scholarly journals Exploring the Scope of Tandem Palladium and Isothiourea Relay Catalysis for the Synthesis of α-Amino Acid Derivatives

Molecules ◽  
2020 ◽  
Vol 25 (10) ◽  
pp. 2463
Author(s):  
Jacqueline Bitai ◽  
Alexandra M. Z. Slawin ◽  
David B. Cordes ◽  
Andrew D. Smith
Keyword(s):  
Amino Acid ◽  
Transition State ◽  
Quaternary Ammonium ◽  
Palladium Catalyst ◽  
Quaternary Ammonium Salts ◽  
Sigmatropic Rearrangement ◽  
Ammonium Salts ◽  
Amino Acid Derivatives ◽  
Substitution Pattern

The scope and limitations of a tandem N-allylation/[2,3]-rearrangement protocol are investigated through the incorporation of a variety of functional groups within an allylic phosphate precursor. This method uses readily accessible N,N-dimethylglycine aryl esters and functionalized allylic phosphates, forming quaternary ammonium salts in situ in the presence of a palladium catalyst. Subsequent enantioselective [2,3]-sigmatropic rearrangement, promoted by the chiral isothiourea tetramisole, generates α-amino acid derivatives with two contiguous stereocenters. The incorporation of electron-withdrawing ester and amide groups gave the best results, furnishing the desired products in moderate to good yields (29–70%), with low diastereocontrol (typically 60:40 dr) but high enantioselectivity (up to 90:10 er). These results indicate that substrate–catalyst interactions in the proposed transition state are sensitive to the substitution pattern of the substrates.

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