1,721,090 research outputs found
Computer-Assisted Design and Synthetic Applications of Chiral Enol Borinates: Novel, Highly Enantioselective Aldol Reagents
No full textWe have recently described the development of a quantitative transition state model for the prediction of stereoselectivity in the boron-mediated aldol reaction. This model provides qualitative insights into the factors contributing to the stereochemical outcome of a variety of reactions of synthetic importance. The force field model was used to assist the design and preparation of new chiral boron ligands derived from menthone. The chiral boron enolates were employed in various stereoselective processes, including the addition to chiral aldehydes and the reagent-controlled total synthesis of (3S,4S)-statine. The chiral enolates derived from alpha-halo and alpha-oxysubstituted thioacetates were added to aldehydes and imines. Addition to imines leads to the enantioselective synthesis of chiral aziridines, a formal total synthesis of (+)-thiamphenicol, and a new highly efficient synthesis of the paclitaxel (taxol®) C-13 side-chain and taxol semisynthesis from baccatin III. The stereochemical outcome of the addition to imines was rationalised with the aid of computational studies. Enantioselective addition reactions of the chiral boron enolate derived from thioacetate have successfully been applied to solid phase bound aldehydes to give aldol products in comparable yields and enantioselectivities to the usual solution conditions
2-(2-Hydroxyaryl)cinnamic amides: a new class of axially chiral molecules
No full textThe syntheses of several differently substituted amides formally derived from a chiral amine, either E-2-(2-hydroxyphenyl)cinnamic acid or both E- and Z-2-(2-hydroxynaphthyl)cinnamic acid, are reported. These molecules display a restricted rotation about the C2-Caryl bond. The barriers to rotation about the C2-Caryl bond were measured by the dynamic 1H NMR and were found to vary between 11.8 and 24.5 kcal mol-1, depending on the substitution. In particular, E-2-(2-hydroxynapthyl)cinnamic amides, displayed a high barrier to rotation (ΔGc‡ = 24.4 kcal mol-1) and could be isolated in both diastereomerically pure forms at room temperature. The X-ray structure of one E-2-(2-hydroxynapthyl)cinnamic amide, was resolved, enabling for the determination of the absolute configuration of the chiral axis (aR)
Copper-catalysed Enantioselective Desymmetrisation of meso Cyclic Allylic Bis(diethyl phosphates) with Organozinc Reagents
No full textChiral (salen)Co(III)(N-benzyl-L-serine) derived phosphites: monodentate P-ligands for enantioselective catalytic applications
No full textDiacetoneglucose Complexes of Manganese(II) and Iron(II) and Their Organometallic Derivatization.
No full textSynthesis and screening of new chiral ligands for the copper-catalysed enantioselective allylic substitution
No full textA Catalytic and Enantioselective Desymmetrization of Meso Cyclic Allylic Bisdiethylphosphates with Organozinc Reagents
No full textSupraBox: a New Class of Chiral Supramolecular Oxazoline Ligands
No full textA new class of oxazoline ligands, named SupraBox, was studied. These ligands possess an additional urea functionality to generate supramolecular bidentate ligands in transition metal complexes, by the establishment of hydrogen bonds between the urea N-hydrogens of one ligand and the carbonyl oxygen of a second one. A library of 16 SupraBox ligands was prepared containing five differently substituted oxazoline nuclei, four linkers and three different urea substituents. The formation of copper(II) and palladium(II) complexes was investigated by MS, UV-Vis and 1H-NMR spectroscopy. The SupraBox library was screened in the copper catalyzed asymmetric benzoylation of vic-diols. Good selectivities were obtained in the kinetic resolution of racemic hydrobenzoin (ee up to 86% and selectivity (s) = 28) and in the desymmetrization of meso-hydrobenzoin (ee up to 88%)
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