Search results for "Chiral"

Synthetic Studies towards Pectenotoxin-2: Synthesis of the Nonanomeric 10-epi-ABCDE Ring Segment by Kinetic Spiroketalization

2011

The synthesis of the nonanomeric 10-epi-ABCDE ring system of pectenotoxin-2 has been achieved by using a kinetic spiroketalization reaction. The synthesis of the spiroketalization precursor was achieved through a cross-metathesis/hydro-genation sequence. The formation of the epi-C10 isomer resulted from an unexpected anti-Felkin selective addition of organometallic nucleophiles to the advanced CDE ring precursor. This addition reaction was investigated with differently protected α,β-dioxygenated model aldehydes, which displayed similar anti-Felkin selectivities with organometallic nucleophiles.

Synergy of Axial and Point Chirality to Construct Helical N -Heterotriangulene-Based Supramolecular Polymers

2018

Molecular Self-Assembly of Enantiopure Heptahelicene-2-Carboxylic Acid on Calcite (1014)

2012

Chirality can have a decisive influence on the molecular structure formation upon self-assembly on surfaces. In this paper, we study the structures formed by enantiopure (M)-heptahelicene-2-carboxylic acid ((M)-[7]HCA) on the calcite (10 (1) over bar4) cleavage plane under ultrahigh vacuum conditions. Previous noncontact atomic force microscopy studies have revealed that the racemic mixture of (M)-[7]HCA and (P)-[7]FICA (1:1) self-assembles into well-defined molecular double rows that are oriented along the calcite [01 (1) over bar0] direction. Here, we investigate the enantiopure (M)[7]HCA compound, resulting in distinctly different molecular structures upon deposition onto calcite (10 (1)…

A Co2O2 metallacycle exclusively supported by l-valine

2008

Abstract [Co2(OH)2( l -valine)4]·2.5H2O has been prepared under hydrothermal conditions and constitutes the first example of a [Co2O2] core supported exclusively by aminoacids. This synthetic dimetallic model for redox active metalloenzymes is one of the few binary aminoacid compounds of biologically relevant metal ions that has been structurally characterized, showing the possibilities of this synthetic approach for preparation of models in bioinorganic chemistry.

Amino Acid Esters as Chiral Auxiliary Groups in Lewis Acid Catalyzed Reactions of Electron-rich Siloxydienes with Imines

1990

Retro-Diels-Alder Protocol for the Synthesis of Pyrrolo[1,2-a]pyrimidine and Pyrimido[2,1-a]isoindole Enantiomers

2013

A simple protocol was introduced to prepare several enantiomerically pure heterocycles by using (–)-(1R,2R,3S,4S)-3-aminonorbornene-2-carboxylic acid as a chiral auxiliary. The protocol is based on a domino ring-closure reaction, in which the relative configuration of the new asymmetric center is controlled by the stereochemistry of the amino acid, followed by a microwave-induced retro-Diels–Alder reaction.

ChemInform Abstract: Solution-, Solid-Phase, and Fluorous Synthesis of β,β-Difluorinated Cyclic Quaternary α-Amino Acid Derivatives: A Comparative St…

2008

The diastereoselective synthesis of cyclic β,β-difluorinated α-amino acid derivatives bearing a quaternary stereocenter is described. The process relies on the chemo- and diastereoselective addition of allylic organometallic reagents to fluorinated α-imino esters and a subsequent ring-closing metathesis reaction (RCM). Complete selectivity in the nucleophilic addition was achieved with (R)-phenylglycinol methyl ether as a chiral auxiliary. The resulting amino acids were introduced into peptide chains, which could facilitate the preparation of potentially bioactive dipeptide derivatives. In addition, the solution synthesis of these cyclic fluorinated α-amino acids was successfully adapted to…

ChemInform Abstract: Amino Acid Esters as Chiral Auxiliary Groups

2010

ChemInform Abstract: Enantioselective Synthesis of α-Quaternary Amino Acids by Alkylation of Deprotonated α-Aminonitriles.

2015

An α-alkylation of deprotonated α-amino nitriles, prepared from chiral phenyldioxanamine (I) by Strecker reaction, leads to α-quaternary arylglycines with high optical purity after hydrolysis and oxidative cleavage of the chiral auxiliary.

ChemInform Abstract: New Strategy for the Stereoselective Synthesis of Fluorinated β-Amino Acids.

2010

Racemic and chiral nonracemic α-substituted and α-unsubstituted β-fluoroalkyl β-amino acid derivatives 6 and 9 have been synthesized in two steps starting from fluorinated imidoyl chlorides 1 and ester enolates. This approach is based on the chemical reduction of previously obtained γ-fluorinated β-enamino esters 4 by using ZnI2/NaBH4 in a nonchelated aprotic medium (dry CH2Cl2) as the reducing agent. A metal-chelated six-membered model has been suggested to explain the stereochemical outcome of the reduction reaction. The process takes place with high yields and with moderate to good diastereoselectivity. The best results related to diastereoselective reduction of chiral β-enamino esters 4…