Search results for "selective synthesis"
showing 10 items of 430 documents
A DFT study on the chiral synthesis of R-phenylacetyl carbinol within the quantum chemical cluster approach
2017
Abstract The reaction pathway leading to R-phenylacetyl carbinol within the quantum chemical cluster approach is addressed by means of density functional theory (DFT) calculations. The study includes calculation of Fukui functions, activation free energies, and potential energy surface scans, both in gas and solution phase. The protonation states of the nitrogen atoms of the pyrimidine moiety are determined. The reaction appears to be slightly exergonic (ΔG 0 = −5.6 and −4.0 kcal/mol for gas and solution phase, respectively) following a concerted synchronous mechanism having activation free energy barriers of 16.2 and 13.3 kcal/mol, in gas phase and solution phase, respectively.
Multigram Scale Enzymatic Synthesis of (R)-1-(4′-Hydroxyphenyl)ethanol Using Vanillyl Alcohol Oxidase
2018
The enantioselective oxyfunctionalisation of C−H bonds is a highly interesting reaction, as it provides access to chiral alcohols that are important pharmaceutical building blocks. However, it is hard to achieve using traditional methods. One way in which it can be achieved is through the action of oxidative enzymes. Although many reports of the oxyfunctionalisation capabilities of enzymes at an analytical scale have been published, reports on the use of enzymes to achieve oxyfunctionalisation on a synthetically relevant scale are fewer. Here, we describe the scale-up of the conversion of 4-ethylphenol to (R)-1-(4′-hydroxyphenyl)ethanol using the flavin-dependent enzyme vanillyl alcohol oxi…
Asymmetric synthesis of 3,3′-pyrrolidinyl-dispirooxindoles via a one-pot organocatalytic Mannich/deprotection/aza-Michael sequence
2016
Chemical communications 52, 2249-2252 (2016). doi:10.1039/C5CC10057G
Reversed phase liquid chromatography for the enantioseparation of local anaesthetics in polysaccharide-based stationary phases. Application to biodeg…
2020
[EN] A comprehensive study on the chiral separation of bupivacaine, mepivacaine, prilocaine and propanocaine with eight commercial polysaccharide-based chiral stationary phases (CSPs) in reversed phase conditions compatible with MS detection is performed. Methanol and acetonitrile are used as organic modifiers. Retention and resolution values obtained for each compound in the different CSPs and mobile phases are compared. The polysaccharide-based CSPs tested present different enantioselectivity towards the analytes. From the results, the experimental conditions for determining the enantiomers of bupivacaine, mepivacaine, prilocaine and propanocaine in saline aqueous samples using MS detecti…
Aminosäureester als chirale Hilfsgruppen in Lewis-Säure-katalysierten Diels-Alder-Reaktionen
1990
Amino Acid Esters as Chiral Auxiliaries in Lewis Acid Catalyzed Diels-Alder Reactions Cyclopentadiene, cyclohexadiene and alkyl-substituted butadienes react with N-acryloyl-, N-crotonoyl- and N-(4-nitro-cinnamoyl)-(S)-proline benzyl and allyl ester in the presence of Lewis acids to give the cycloadducts in high yields and with stereoselectivities of up to 97:3 for the endo isomers. The sense of the asymmetric induction in these reactions can be directed by the use of differently coordinating catalysts (e.g. TiCl4: (2R):(2S) = 96:4; EtAlCl2: (2R):(2S) = 10:90 at 0°C). In the TiCl4-catalyzed reactions with the fumaric acid derivatives the ratio of the diastereomers reaches values of up to 112…
Asymmetric Addition and Cycloaddition Reactions with Ylidene‐Five‐Membered Heterocycles
2021
Five-membered heterocycles bearing an exocyclic double bond have been successfully used as substrates in asymmetric addition and cycloaddition reactions. Ylidene-heterocycles are attractive substrates due to their high functionalization and the presence of an electrophilic conjugated exocyclic double bound that can participate in nucleophilic addition reactions as well as cycloaddition reactions, which may be triggered by the formation of aromatic intermediates or products in many cases. During the last decades, catalytic methodologies have been developed using ylidene-heterocycles as substrates in order to synthesize useful optically active heterocyclic derivatives. 4-Ylidene-pyrazol-5-one…
Enantioselective Addition of Dimethylzinc to Aldehydes Catalyzed by N-Substituted Mandelamide-Ti(IV) Complexes.
2005
Abstract Amides derived from ( S )-(+)-mandelic acid in the presence of titanium isopropoxide catalyze the enantioselective addition of dimethylzinc to aromatic aldehydes with good yields and ee up to 90%.
Synthesis of new polydentate oxalamide-based ligands as chiral catalysts for the enantioselective addition of diethylzinc to benzaldehyde
2006
New polydentate oxalamide-based ligands have been studied as chiral catalysts in the enantioselective addition of diethylzinc to benzaldehyde
ChemInform Abstract: A Catalytic Highly Enantioselective Direct Synthesis of 2-Bromo-2-nitroalkan-1-ols Through a Henry Reaction.
2009
Highly enantiomerically enriched 2-bromo-2-nitroalkan-1-ols are prepared by direct condensation of aliphatic and aromatic aldehydes with bromonitromethane in the presence of a catalytic amount of copper(II) acetate and a C1-symmetric camphor-derived amino pyridine ligand.
Enantioselective synthesis of 2-substituted-1,4-diketones from (S)-mandelic acid enolate and α,β-enones
2006
[EN] An approach for the synthesis of chiral non-racemic 2-substituted-1,4-diketones from (S)-mandelic acid and ¿,ß-enones has been developed. The reaction of lithium enolate of the 1,3-dioxolan-4-one derived from optically active (S)-mandelic acid and pivalaldehyde with ¿,ß-unsaturated carbonyl compounds proceeds readily to give the corresponding Michael adducts in good yields and with high diastereoselectivities. The addition of HMPA (3 equiv) reverses and strongly enhances the diastereoselectivity of the reaction. A change in the reaction mechanism from a lithium catalyzed to the one where catalysis has been suppressed by coordination of HMPA to lithium is proposed to explain these resul…