Search results for "Enantioselective"
showing 10 items of 427 documents
Enantioselective synthesis of fluorinated alpha-amino acids and derivatives in combination with ring-closing metathesis: intramolecular pi-stacking i…
2001
[reaction: see text]. Hydride reduction of C=N bonds stereocontrolled by intramolecular pi-stacking interactions of 1-naphthylsulfinyl and N-aryl groups, nonoxidative Pummerer rearrangement, and ring-closing metathesis are efficiently combined in a highly stereoselective entry to enantiomerically pure cyclic and acyclic fluorinated beta-amino alcohols and alpha-amino acid derivatives, respectively.
Microwave-Assisted Tandem Organocatalytic Peptide-Coupling Intramolecular aza-Michael Reaction: α,β-UnsaturatedN-Acyl Pyrazoles as Michael Acceptors
2014
Conjugated N-acyl pyrazoles have been successfully employed in the organocatalytic enantioselective intramolecular aza-Michael reaction as ester surrogates. Bifunctional squaramides under microwave irradiation provided the best results in this transformation. Furthermore, this protocol has been combined with a peptide-coupling reaction in a tandem sequence. The final products were easily converted into the corresponding ethyl esters.
Recent Advances in Enantioselective Desymmetrizations of Prochiral Oxetanes
2021
Abstract Strain relief of oxetanes offers a plethora of opportunities for the synthesis of chiral alcohols and ethers. In this context, enantioselective desymmetrization has been identified as a powerful tool to construct molecular complexity and this has led to the development of elegant strategies on the basis of transition metal, Lewis acid, and Brønsted acid catalysis. This review highlights recent examples that harness the inherent reactivity of prochiral oxetanes and offers an outlook on the immense possibilities for synthetic application.
Enantioselective Synthesis of (−)-Dihydrocodeine and Formal Synthesis of (−)-Thebaine, (−)-Codeine, and (−)-Morphine from a Deprotonated α-Aminonitri…
2014
The α-benzylation of a deprotonated bicyclic α-aminonitrile, followed by Noyori's asymmetric transfer hydrogenation combined with the Grewe cyclization onto a symmetrical A-ring precursor, are the key steps of a short and high-yielding enantioselective synthesis of the morphinan (-)-dihydrocodeine. This compound can be converted to (-)-thebaine in high yield by known transformations, while (-)-codeine and (-)-morphine are available from an advanced intermediate.
Organocatalytic enantioselective synthesis of quinolizidine alkaloids (+)-myrtine, (-)-lupinine, and (+)-epiepiquinamide
2011
The organocatalytic synthesis of quinolizidine alkaloids (+)-myrtine, (-)-lupinine, and (+)-epiepiquinamide is described. It involved, as the key step, an enantioselective intramolecular aza-Michael reaction (IMAMR) catalyzed by Jorgensen catalyst I, affording the common precursor with high enantioselectivity. This compound was subsequently transformed into the three alkaloids in a highly diastereoselective manner. (C) 2011 Elsevier Ltd. All rights reserved.
Natural eutectogels: sustainable catalytic systems for C–C bond formation reactions
2021
Natural eutecto gels were prepared combining properties of amino acids with the ones of deep eutectic solvents. Soft materials obtained were fully characterised determining the gel-sol transition temperatures and analysing mechanical and morphological features through rheological measurements and polarised optical microscopy. All eutecto gels were tested as catalytic reaction media for the enantioselective aldol reaction and, the best performing one was also used to carry out the Michael addition. In both cases, eutecto gels proved to have a great potential as sustainable reaction media, allowing to perform processes under mild conditions, obtaining excellent yields and, in some cases, also…
A Decade of Advance in the Asymmetric Vinylogous Mannich Reaction
2016
When the principle of vinylogy is applied to imines as electrophiles, the so-called vinylogous Mannich reaction (VMR), γ-aminocarbonyl (such as butenolides) and β-aminocarbonyl compounds are generated in a very efficient manner. The asymmetric version of this vinylogous Mannich reaction gives access to highly functionalized chiral synthons, which are suitable for further transformations. The versatility of this methodology is exemplified with the synthesis of several alkaloids and natural products. 1 Introduction 2 Asymmetric Vinylogous Mannich Reactions (VMR) with 2-Silyloxyfurans and 2-Silyloxypyrroles 3 Asymmetric VMR with Acyclic Silyl Dienolates and Silyl Dienol Ketene Acetals 4 Asymm…
Highly enantioselective aza-Henry reaction with isatin N-Boc ketimines.
2014
A highly enantioselective aza-Henry reaction with isatin N-Boc ketimines using a Cu(II)–BOX complex as a catalyst is described. The reaction, which does not require protection of the N1 atom, provides the corresponding nitroamines bearing a quaternary stereocentre with high yields and enantiomeric excesses (up to 99.9%).
Concise asymmetric synthesis of Linezolid through catalyzed Henry reaction
2013
A new asymmetric synthesis of the antibiotic Linezolid was performed through a copper-catalyzed Henry reaction as the key step. The use of camphor-derived aminopyridine ligands helped to improve the yields of the chiral precursor and to obtain Linezolid in good overall yield and enantiomeric excess.
A catalytic highly enantioselective direct synthesis of 2-bromo-2-nitroalkan-1-ols through a Henry reaction.
2008
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 camphorderived amino pyridine ligand. Blay Llinares, Gonzalo, Gonzalo.Blay@uv.es ; Hernandez Olmos, Victor, Victor.Hernandez@uv.es ; Pedro Llinares, Jose Ramon, Jose.R.Pedro@uv.es