Search results for "Química orgànica"
showing 10 items of 84 documents
Intramolecular Cycloaddition Azomethine Ylides and α-(Trifluoromethyl)styrenes as Dipolarophiles
2019
The synthesis of polycyclic fluorinated tertiary amines has been accomplished by means of an intramolecular azomethine ylide cycloaddition with fluorinated dipolarophiles. Thus, tri- and tetracyclic fused pyrrolidines bearing a quaternary trifluoromethyl group were obtained in moderated yields in a stereoselective manner. This is one of the few examples reported in the literature of intramolecular 1,3-dipolar cycloaddition of azomethine ylides with fluorinated dipolarophiles. Initial attempts of the asymmetric version of the process have been performed, but low levels of diastereoselectivity were achieved.
Visible-light-accelerated amination of quinoxalin-2-ones and benzo[1,4]oxazin-2-ones with dialkyl azodicarboxylates under metal and photocatalyst-fre…
2021
A direct sp3 C-H amination of cyclic amines (dihydroquinoxalinones and dihydrobenzoxazinones) with dialkyl azo dicarboxylates accelerated by visible-light irradiation under metal and photocatalyst-free conditions is described. This protocol features very mild reaction conditions for the synthesis of aminal quinoxaline and benzoxazine derivatives with good to high yields (up to 99%). These aminal derivatives respresent versatile building blocks for the divergent synthesis of quinoxalin-2-one derivatives.
Approach Matters : The Kinetics of Interfacial Inverse-Electron Demand Diels-Alder Reactions
2017
Rapid and quantitative click functionalization of surfaces remains an interesting challenge in surface chemistry. In this regard, inverse electron demand Diels Alder (IEDDA) reactions represent a promising metal-free candidate. Herein, we reveal quantitative surface functionalization within 15 min. Furthermore, we report the comprehensive effects of substrate stereochemistry, surrounding microenvironment and substrate order on the reaction kinetics as obtained via a combination of XPS and surface-bound mass spectrometry (DART-MS).
Merging Visible-Light-Photoredox and Nickel Catalysis
2015
A new combination: The merging of visible‐light‐photoredox catalysis and nickel catalysis has been successfully achieved for cross‐coupling reactions. The synthetic scope and limitations of the combination of nickel and photoredox catalysis for Csp3-Csp2 cross‐coupling reactions is discussed.
Organic Monolayers by B(C6F5)3-Catalyzed Siloxanation of Oxidized Silicon Surfaces
2017
Inspired by the homogeneous catalyst tris(pentafluorophenyl) borane [B(C6F5)3], which acts as a promotor of Si-H bond activation, we developed and studied a method of modifying silicon oxide surfaces using hydrosilanes with B(C6F5)3 as the catalyst. This dedihydrosiloxanation reaction yields complete surface coverage within 10 min at room temperature. Organic monolayers derived from hydrosilanes with varying carbon chain lengths (C8-C18) were prepared on oxidized Si(111) surfaces, and the thermal and hydrolytic stabilities of the obtained monolayers were investigated in acidic (pH 3) medium, basic (pH 11) medium, phosphate-buffered saline (PBS), and deionized water (neutral conditions) for …
Enantioselective Friedel-Crafts reaction of hydroxyarenes with nitroenynes to access chiral heterocycles via sequential catalysis
2021
Naphthols, hydroxyindoles and an activated phenol are reacted with differently substituted (E)-nitrobut-1-en-3-ynes using the commercially available Rawal's chiral squaramide. The corresponding β-nitroalkynes were obtained with good yields and excellent enantioselectivities. Moreover, dihydronaphthofurans can be accessed via silver catalysed cyclization in a tandem one-pot procedure, with high preservation of the optical purity.
Enantioselective Synthesis of 5-Trifluoromethyl-2-oxazolines under Dual Silver/Organocatalysis.
2019
[EN] The first enantioselective formal [3 + 2] cycloaddition between ¿-isocyanoesters and trifluoromethylketones to give 5-trifluoromethyl-2-oxazolines bearing two contiguous stereogenic centers, one of them being a quaternary stereocenter substituted with a CF3 group, has been developed. The reaction is based upon a multicatalytic approach that combines a bifunctional Brønsted base-squaramide organocatalyst and Ag+ as Lewis acid. The reaction could be achieved with a range of aryl and heteroaryl trifluoromethyl ketones, and the resulting oxazolines were obtained with good to excellent diastereo- and enantioselectivity.
Mg/BOX complexes as efficient catalysts for the enantioselective Michael addition of malonates to β-trifluoromethyl-α,β-unsaturated ketones and their…
2021
Abstract Magnesium (II)-BOX complexes catalyze the enantioselective Michael addition of malonates to β-trifluoromethyl enones and their N-sulfonyl imines to give ketones or (E)-enamines bearing a trifluoromethylated stereogenic center, respectively, with good yields and high enantiomeric excesses. Magnesium complexes proved to be more active and stereoselective than zinc and copper analogues in these reactions.
Copper-catalysed enantioselective Michael addition of malonic esters to β-trifluoromethyl-α,β-unsaturated imines
2017
[EN] Copper triflate-BOX complexes catalyse the enantioselective conjugate addition of methyl malonate to beta-trifluoromethyl-alpha,beta-unsaturated imines to give the corresponding enamines bearing a trifluoromethylated stereogenic centre with good yields, and diastereo- and enantioselectivities. The usefulness of the method has been shown with the synthesis of optically active beta-trifluoromethyl delta-amino esters and optically active trifluoromethyl piperidones.
Diarylprolinol as a Ligand for Enantioselective Alkynylation of Cyclic Imines
2017
An easily accessible prolinol derived ligand, (S)-bis(3,5-bis(trifluoromethyl)phenyl)(pyrrolidin-2-yl)methanol, has been efficiently applied in the catalytic enantioselective addition of terminal alkynes to cyclic imines using dimethylzinc (Me2Zn) under mild reaction conditions. The developed catalytic system led to chiral propargylic sulfamidates with high yields (up to 97%) and excellent enantioselectivities (up to 97% ee).