Search results for "Stereoselectivity"
showing 10 items of 325 documents
Disposition and Anticoagulant Activity of the Enantiomers of Phenprocoumon in Phenobarbital Pretreated Rats
1978
The purpose of this study was to assess in rats the effect of enzyme induction on the stereoselective disposition and anticoagulant activity of phenprocoumon.
3.17 Synthetically Derived Auxiliaries: Phosphorus Derivatives
2012
This chapter aims to give an overall view of chiral-pool based asymmetric synthesis of organophosphorus compounds more particularly bearing the chirality on the phosphorus atom (P-stereogenic). The enantiomerically pure organophosphorus compounds can be obtained either by resolution of the racemate or by stereoselective synthesis using particularly ephedrine or sparteine as the main chiral auxiliaries and borane as a P(III)-protecting group.
Stereoselective Metabolic Activation of Dibenzo[a,l]Pyrene in the Human Mammary Carcinoma Cell Line MCF-7 Results in Formation of (-)-antiand (+)-syn…
1996
Abstract Dibenzo[a,l]pyrene (DB[a,l]P) is an important polycyclic aromatic hydrocarbon because of possible human exposure and its exceptionally high carcinogenicity in rodents. We examined the metabolism of DB[a,l]P and the formation of DB[a,l]P-DNA adducts in the human mammary carcinoma cell line (MCF-7). Analysis of the DNA adducts by 33P-postlabeling, immobilized boronate chromatography, HPLC and TLC demonstrated that DB[a,l]P is stereoselectively metabolized to specific optical isomers of DB[a,l]P-11,12-diol-13,14-epoxide (DB[a,l]PDE). The major anti-DB[a,l]PDE adduct formed in DB[a,l]P-treated MCF-7 cells resulted from reaction of (-)-anti-DB[a,l]PDE with DNA whereas the two major syn-…
Hydrophobically directed aldol reactions: polystyrene-supported L-proline as a recyclable catalyst for direct asymmetric aldol reactions in the prese…
2007
A simple synthetic methodology for the preparation of a polystyrene- supported L-proline material is reported, and this material has been used as catalyst in direct asymmetric aldol reactions between several ketones and arylaldehydes to furnish aldol products in high yields and stereoselectivities. Screening of solvents showed that these reactions take place only in the presence of water or methanol, at lower levels of conversion in the latter case. This solvent effect, coupled with the observed high stereoselectivities, has been ex- Introduction In the last decade organocatalysis has became a field of great interest.[1] Organocatalysts are metal-free small organic molecules that are able t…
Highly regio- and stereoselective iodocyclization of chiral 3-alkoxycarbonyl-4-propenyl-2,2-dimethyl-1,3-oxazolidines: a computational investigation
1999
The iodocyclization of allylic carbamates 3a and 3b proceeded with high regio- and stereoselection to give 2-oxobicyclo[4.3.0]nonane 5a as the major product. Both the regio- and diastereoselection of the reaction were investigated with the help of molecular mechanics and quantomechanical calculations. The energetic difference between the competing transition states TS-5a and TS-5b is in good agreement with the experimental results and from the calculated transition structures it appears that steric factors direct the discrimination.
ChemInform Abstract: Auxiliary-Controlled Stereoselective Enolate Protonation: Enantioselective Synthesis of cis and trans Annulated Decahydroquinoli…
2010
Abstract The diastereoselective synthesis of the octahydroquinoline enone precursor of pumiliotoxin C is achieved via tandem Mannich-Michael reaction on N-galactosyl imines. Conjugate cuprate addition to the bicyclic enone stereoselectively forms the trans annulated 4a- epi -pumiliotoxin C skeleton in the presence of the carbohydrate auxiliary, and the cis annulated pumiliotoxin C skeleton in its absence.
Direct catalytic cross-coupling of alkenyllithium compounds
2015
A catalytic method for the direct cross-coupling of alkenyllithium reagents with aryl and alkenyl halides is described. The use of a catalyst comprising Pd-2(dba)(3)/XPhos allows for the stereoselective preparation of a wide variety of substituted alkenes in high yields under mild conditions. In addition (1-ethoxyvinyl) lithium can be efficiently converted into substituted vinyl ethers which, after hydrolysis, give readily access to the corresponding methyl ketones in a one pot procedure.
N-Glycosyl Amides as Glycosyl Donors in Stereoselective Glycosylation Reactions
2004
Due to their high stability, N-glycosyl amides have so far not been considered as glycosyl donors for glycosylation reactions. Two new procedures for the cleavage of the anomeric amide functionality under mild reaction conditions and further stereoselective in situ conversions of the activated glycosyl donors with alcohols and amines to give β-configured O- and N-glycosides are described in this article.
A DFT study of the mechanism and selectivities of the [3 + 2] cycloaddition reaction between 3-(benzylideneamino)oxindole and trans -β-nitrostyrene
2016
The mechanism and regioselectivities and stereoselectivities of the [3 + 2] cycloaddition (32CA) reaction of 3-(benzylideneamino) oxindole (AY) and trans-β-nitrostyrene have been studied using both B3LYP and ωB97XD density functional theory methods together with the standard 6-31G(d) basis set. Four reactive pathways associated with the ortho and meta regioselective channels and endo and exo stereoselective approaches modes have been explored and characterized. While the B3LYP functional fails to predict the experimental regioselectivity, the ωB97XD one succeeds to predict the experimentally observed meta regioselectivity favoring the formation of meta/endo cycloadduct as the major isomer. …
Diels-Alder Reactions of 2-Azabutadienes with Aldehydes: Ab Initio and Density Functional Theoretical Study of the Reaction Mechanism, Regioselectivi…
1997
The Diels−Alder reaction of 2-azabutadiene with aldehydes has been studied using high level ab initio molecular orbital and density functional methods. Multiconfigurational calculations were carried out on the concerted and stepwise mechanisms. At the CASPT2F/6-31G*//CASSCF/6-31G* level of theory, the [π4s + π2s]-cycloaddition of 2-azabutadiene with formaldehyde is predicted to be a concerted reaction, in good agreement with the experimental evidence. The regio- and stereoselectivity of the reaction was studied at the HF/6-31G*, MP2/6-31G*, and Becke3LYP/6-31G* levels of theory. The density functional calculations appears to give a good description of the basic features of the reaction. The…