Search results for "Michael"

Asymmetric Organocatalytic Michael Addition–Cyclization Cascade of Cyclopentane-1,2-dione with Substituted α,β-Unsaturated Aldehydes

2017

An asymmetric organocatalytic Michael addition–cyclization cascade reaction has been developed using cyclopentane-1,2-dione as a Michael donor and α,β-unsaturated aldehydes as Michael acceptors. Bicyclic hemiacetals were obtained in excellent yields and enantioselectivities. On the basis of the results, a one-pot reaction has been developed to obtain chiral 3-substituted cyclopentane-1,2-diones and substituted dihydropyrans in good yields and excellent enantioselectivity.

CaCl2, Bisoxazoline, and Malonate: A Protocol for an Asymmetric Michael Reaction

2015

A mild protocol for the asymmetric Michael addition of dimethyl malonate to various α,β-unsaturated carbonyl compounds was developed. The salient feature of this methodology is that a cheap and environmentally friendly Lewis acid, CaCl2, was used as a catalyst. An aminoindanol- and pyridine-derived ligand provided in the presence of CaCl2 Michael adducts in moderate to high enantioselectivities. The scope of the reaction was demonstrated.

"I just saw someone die omfg" : multimodal representations of the shooting of Michael Brown on Tumblr

2015

Tämän tutkielman aiheena on tutkia suosiotaan kasvattavan sosiaalisen median sivuston Tumblrin rakentamia representaatioita postauksissa, jotka jatkuvasti käsittelivät tavalla tai toisella Yhdysvalloissa, Fergusonin kaupungissa elokuussa 2014 tapahtunutta poliisin ja tummaihoisen nuoren miehen, Michael Brownin, välistä yhteenottoa jossa Brown sai surmansa. Ampumatapaus ja sitä seuranneet mielenosoitukset saivat huomiota sekä perinteisessä että sosiaalisessa mediassa. Tutkielmani tarkoitus on selvittää kuinka kyseiseen ampumatapaukseen liittyvissä postauksissa Tumblrissa tapausta representoitiin, eli millaisia merkityksiä siitä rakennettiin multimodaalisin eli monikanavaisin keinoin. Aineist…

Las victorias de Bush

2001

Squaramide-Catalyzed Enantioselective Michael Addition of Pyrazol-3- ones to ortho-Quinone Methides

2020

A bifunctional squaramide catalyzed the enantioselective Michael addition of pyrazol-3- ones to ortho-quinone methides, generated in situ from 2-(1-tosylalkyl)phenols is presented. The corresponding chiral pyrazolones are obtained with good to excellent yields (27-98%) and enantiomeric excess (14-99% ee).

Comparative computational analysis of different active site conformations and substrates in a chalcone isomerase catalyzed reaction.

2006

Chalcone isomerase catalyzes the transformation of chalcones to flavanones. We present a computational study of the rate-limiting chemical step, an intramolecular Michael addition of a 2'-oxyanion to the alpha,beta-double bound. By using quantum mechanical/molecular mechanical hybrid methods we traced the free-energy profiles associated with the reaction of two different substrates (chalcone and 6'-deoxychalcone) in two different conformations of the active site that are described in the different crystallographic structures available. We have obtained significant differences (about 4 kcal/mol) in the free-energy barriers calculated for the two active sites. According to our results, the ac…

A Novel Strategy to Study Electrostatic Effects in Chemical Reactions: Differences between the Role of Solvent and the Active Site of Chalcone Isomer…

2015

The electrostatic behavior of active site residues in enzyme catalysis is quite different from that of water molecules in solution. To highlight the electrostatic differences between both environments, we propose a QM/MM strategy to study the role of the environment in chemical reactions. The novelty of the present communication is that free energy surfaces are generated by means of two distinguished reaction coordinates: a solute coordinate and the electrostatic potential created by the environment. This is applied to analyze the origin of catalysis in the transformation of a chalcone into a flavanone, a Michael addition that requires the desolvation of the nucleophile.

A molecular electron density theory (MEDT) study of the role of halogens (X2= F2, Cl2, Br2and I2) on the aza-Michael-addition reactions

2020

Using the Molecular Electron Density Theory (MEDT), a set of uncatalyzed and X2 molecule-catalyzed (X2 = F2, Cl2, Br2, or I2) aza Michael addition reactions (aza-MARs) between pyrrolidine (PYR) and methyl acrylate (MA) have been studied in the gas phase and in dichloromethane (DCM) medium from the kinetics and molecular mechanism aspects. Analysis of the conceptual DFT reactivity indices indicates that the coordination of the X2 molecules to the oxygen of the MA's carbonyl group increases both the softness and the electrophilic character of MA, thus explaining the catalytic role of the X2 molecules. The nucleophilic attack of the nitrogen of PYR on the MA's β conjugated carbon is the rate-d…

ChemInform Abstract: Microwave-Assisted Organocatalytic Enantioselective Intramolecular Aza-Michael Reaction with α,β-Unsaturated Ketones.

2012

The combination of an epi-hydroquinine catalyst and pentafluoropropionic acid accelerates the process.

ChemInform Abstract: Intramolecular Michael Reaction of tert-Butylsulfinyl Ketimines: Asymmetric Synthesis of 3-Substituted Indanones.

2012

The reaction proceeds in the presence of the Ruppert—Prakash reagent (Tms-CF3) with either TBAT or TBAF as a base.