scholarly journals Azirinium ylides from α-diazoketones and 2H-azirines on the route to 2H-1,4-oxazines: three-membered ring opening vs 1,5-cyclization

2015 ◽  
Vol 11 ◽  
pp. 302-312 ◽  
Author(s):  
Nikolai V Rostovskii ◽  
Mikhail S Novikov ◽  
Alexander F Khlebnikov ◽  
Galina L Starova ◽  
Margarita S Avdontseva
Keyword(s):  
Dft Calculations ◽  
Ring Opening ◽  
Membered Ring ◽  
Nucleophilic Attack ◽  
Aziridine Ring

Strained azirinium ylides derived from 2H-azirines and α-diazoketones under Rh(II)-catalysis can undergo either irreversible ring opening across the N–C2 bond to 2-azabuta-1,3-dienes that further cyclize to 2H-1,4-oxazines or reversibly undergo a 1,5-cyclization to dihydroazireno[2,1-b]oxazoles. Dihydroazireno[2,1-b]oxazoles derived from 3-aryl-2H-azirines and 3-diazoacetylacetone or ethyl diazoacetoacetate are able to cycloadd to acetyl(methyl)ketene generated from 3-diazoacetylacetone under Rh(II) catalysis to give 4,6-dioxa-1-azabicyclo[3.2.1]oct-2-ene and/or 5,7-dioxa-1-azabicyclo[4.3.1]deca-3,8-diene-2-one derivatives. According to DFT calculations (B3LYP/6-31+G(d,p)), the cycloaddition can involve two modes of nucleophilic attack of the dihydroazireno[2,1-b]oxazole intermediate on acetyl(methyl)ketene followed by aziridine ring opening into atropoisomeric oxazolium betaines and cyclization. Azirinium ylides generated from 2,3-di- and 2,2,3-triaryl-substituted azirines give rise to only 2-azabuta-1,3-dienes and/or 2H-1,4-oxazines.

Delineating the possibilities for intramolecular interception of the squarate ester cascade through the use of metalated enecarbamates

2000 ◽  
Vol 78 (6) ◽  
pp. 689-696 ◽  
Author(s):  
Jinsung Tae ◽  
Leo A Paquette
Keyword(s):  
Ring Opening ◽  
Membered Ring ◽  
Sequential Treatment ◽  
Nucleophilic Attack ◽  
Ring Strain ◽  
Multistep Process

Highly functionalized and annulated 2,4-cyclooctadienones are formed in a stereoselective manner by sequential treatment of squarate esters with a lithiated enecarbamate (six-membered ring or larger) and a cycloalkenyl- or 1-alkenyllithium reagent. The mechanistic details of this multistep process are presented. Particular attention is drawn to the step that involves intramolecular nucleophilic attack by a proximal oxido anion at the carbamate carbonyl and results in redirection of the cascade. This step is thwarted when five-membered cyclic enecarbamates are employed because of the excessive buildup of ring strain in the associated transition state.Key words: squarate esters, enecarbamates, conrotatory ring opening, intramolecular acylation, alkenyllithium reagents.

scholarly journals Bio-Glycidol Conversion to Solketal over Acid Heterogeneous Catalysts: Synthesis and Theoretical Approach

Catalysts ◽  
2018 ◽  
Vol 8 (9) ◽  
pp. 391 ◽  
Author(s):  
Maria Ricciardi ◽  
Laura Falivene ◽  
Tommaso Tabanelli ◽  
Antonio Proto ◽  
Raffaele Cucciniello ◽  
...  
Keyword(s):  
Dft Calculations ◽  
Theoretical Approach ◽  
Ring Opening ◽  
Heterogeneous Catalysts ◽  
Nucleophilic Attack ◽  
The Novel ◽  
Reaction Conditions

The present work deals with the novel use of heterogeneous catalysts for the preparation of solketal from bio-glycidol. Sustainable feedstocks and mild reaction conditions are considered to enhance the greenness of the proposed process. Nafion NR50 promotes the quantitative and selective acetalization of glycidol with acetone. DFT calculations demonstrate that the favored mechanism consists in the nucleophilic attack of acetone to glycidol concerted with the ring opening assisted by the acidic groups on the catalyst and in the following closure of the five member ring of the solketal.

Reversible Oxidative-Addition and Reductive-Elimination of Thiophene from a Titanium Complex and Its Thermally-Induced Hydrodesulfurization Chemistry

2019 ◽  
Author(s):  
Alejandra Gomez-Torres ◽  
J. Rolando Aguilar-Calderón ◽  
Carlos Saucedo ◽  
Aldo Jordan ◽  
Alejandro J. Metta-Magaña ◽  
...  
Keyword(s):  
Dft Calculations ◽  
Ring Opening ◽  
Thiophene Ring ◽  
Oxidative Addition ◽  
Reductive Elimination ◽  
Thermally Induced ◽  
Titanium Complex

<p>The masked Ti(II) synthon (<sup>Ket</sup>guan)(<i>η</i><sup>6</sup>-Im<sup>Dipp</sup>N)Ti (<b>1</b>) oxidatively adds across thiophene to give ring-opened (<sup>Ket</sup>guan)(Im<sup>Dipp</sup>N)Ti[<i>κ</i><sup>2</sup>-<i>S</i>(CH)<sub>3</sub><i>C</i>H] (<b>2</b>). Complex <b>2</b> is photosensitive, and upon exposure to light, reductively eliminates thiophene to regenerate <b>1</b> – a rare example of early-metal mediated oxidative-addition/reductive-elimination chemistry. DFT calculations indicate strong titanium π-backdonation to the thiophene π*-orbitals leads to the observed thiophene ring opening across titanium, while a proposed photoinduced LMCT promotes the reverse thiophene elimination from <b>2</b>. Finally, pressurizing solutions of <b>2 </b>with H<sub>2</sub> (150 psi) at 80 °C leads to the hydrodesulfurization of thiophene to give the Ti(IV) sulfide (<sup>Ket</sup>guan)(Im<sup>Dipp</sup>N)Ti(S) (<b>3</b>) and butane. </p>

Kinetics of the Imidazolium Ring-Opening of mRNA 5'-cap Analogs in Aqueous Alkali

2006 ◽  
Vol 71 (4) ◽  
pp. 567-578 ◽  
Author(s):  
Alicja Stachelska ◽  
Zbigniew J. Wieczorek ◽  
Janusz Stępiński ◽  
Marzena Jankowska-Anyszka ◽  
Harri Lönnberg ◽  
...  
Keyword(s):  
Electrostatic Interaction ◽  
Ring Opening ◽  
Nucleophilic Attack ◽  
Amino Groups ◽  
Hydroxide Ion ◽  
Methyl Group ◽  
Structural Modifications ◽  
Alkyl Groups ◽  
Imidazolium Ring ◽  
Kinetics Of

Second-order rate constants for the hydroxide-ion-catalyzed imidazolium ring-opening of several mono- and dinucleosidic analogs of mRNA 5'-cap have been determined. Intramolecular stacking of the two nucleobases in the dinucleosidic analogs, m7GpppN (m7G = 7-methylguanosine, N = 5'-linked nucleoside), and electrostatic interaction between the N-alkylated imidazolium ring and phosphate moiety have been shown to shield the m7G moiety against the nucleophilic attack of hydroxide ion. In addition, the effect of methylation of the nucleobase amino groups and replacement of the 7-methyl group with other alkyl groups have been studied. The influence of all the structural modifications studied turned out to be modest, the cleavage rates of the most and least reactive analogs (with the exception of non-phosphorylated nucleosides) differing only by a factor of 5.

scholarly journals Intramolecular N–Me and N–H aminoetherification for the synthesis of N-unprotected 3-amino-O-heterocycles

2021 ◽  
Author(s):  
Mahesh P. Paudyal ◽  
Mingliang Wang ◽  
Juha H. Siitonen ◽  
Yimin Hu ◽  
Muhammed Yousufuddin ◽  
...  
Keyword(s):  
Ring Opening ◽  
Domino Reaction ◽  
Aziridine Ring

A mild Rh-catalyzed method for synthesis of cyclic unprotected N–Me and N–H 2,3-aminoethers using an olefin aziridination–aziridine ring-opening domino reaction has been developed.

Stereoselective Syntheses of 4-Oxa Diaminopimelic Acid and Its Protected Derivatives via Aziridine Ring Opening

2007 ◽  
Vol 9 (21) ◽  
pp. 4211-4214 ◽  
Author(s):  
Hongqiang Liu ◽  
Vijaya R. Pattabiraman ◽  
John C. Vederas
Keyword(s):  
Ring Opening ◽  
Diaminopimelic Acid ◽  
Aziridine Ring ◽  
Stereoselective Syntheses

Construction of isoquinolinone framework from carboxylic ester directed umpolung ring opening of methylenecyclopropanes

2021 ◽  
Author(s):  
Min Shi ◽  
Hao-Zhao Wei ◽  
Yin Wei
Keyword(s):  
Ring Opening ◽  
Nucleophilic Attack ◽  
Reaction Pattern ◽  
Carboxylic Ester ◽  
Anionic Species

An unprecedented reaction pattern of functionalized methylenecyclopropanes (MCPs) has been disclosed in this paper, in which the nucleophilic attack of anionic species onto partially polarity-reversed MCP unit can be realized...

ChemInform Abstract: Five- and Six-Membered Ring Opening of Pyroglutamic Diketopiperazine.

ChemInform ◽  
2010 ◽  
Vol 33 (34) ◽  
pp. no-no
Author(s):  
Dennis A. Parrish ◽  
Lon J. Mathias
Keyword(s):  
Ring Opening ◽  
Membered Ring
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