Peptide Deravatives as New Chiral Ligands for Enantioselective Phenylacetylene Addition to Aldehydes

The asymmetric addition of alkynylzinc to aldehydes is an important method of synthesizing chiral propargyl alcohols, which are important precursors to many chiral organic compounds. Recently, many significant chiral ligands in this area have been disclosed.[1] Use of a short peptide as a catalyst would allow expansion beyond the (still uncharted) repertoire of single amino acids, while conserving the advantages of a small molecule catalyst. To the best of our knowledge,no results of peptide derivatives as chiral ligands in this reaction has been disclosed to date.[2] Herein, we report the initial results of peptide derivatives, which have been used directly as a chiral ligand in this reaction (Scheme 1).     

Synthesis and Catalytic Asymmetric Reaction of Chiral Pyridine Prolinol Derivatives

The enantioselective reduction of prochiral ketones with borane in the presence of a chiral ligand leading to enantiomerically pure secondary alcohols has received considerable attention in recent years. [1] Enantiomerically pure secondary alcohols are important intermediates for the synthesis of various other organic compounds such as halides, esters, ethers, ketones and amines. To the best of our knowledge, the use of pyridine prolinol derivatives in the reduction of ketones has not been reported so far. Thus, it should be of interest to investigate the catalytic a bility of such ligands. We have an ongoing project in the synthesis and application of chiral pyridine derivatives in chiral molecular recognition[2] and we want to evaluate the effect resulting from the introduction of a pyridinyl moiety onto the catalysts. We expect that the cooperation of pyridine unit and chiral prolinol unit in new ligands may result in unique properties for catalytic reaction.     

Synthesis of 7,7’-Disubstituted BINAP and Their Application in Asymmetric Catalytic Reaction

The design of new chiral ligands plays a very important role in the development of transition metal catalyzed asymmetric synthesis. Many chiral diphosphine ligands have been prepared and applied in asymmetric catalytic reactions with excellent enantioselectivities. Among the chiral diphosphine ligands reported, BINAP was found to have been the widest application in the transition metal catalyzed reaction. Recently we have developed a novel oxovanadium (Ⅳ) complex catalyst for the oxidative …     

The Enantioselective Addition of Diethylzinc to Aldehydes Catalyzed by 2-Methylquinoline Derived Chiral Ligands

One of the most important and fundamental synthetic procedures for the establishment of a carbon-carbon bond stereoselectively is the enantioselective addition of organometallic reagents to aldehydes affording chiral secondary alcohols1. In this process, a frequently used method is to perform the reaction in the presence of a chiral ligand such as amino alcohol2. Here, we first report that two new chiral ligands3, which were readily available by the reaction of chiral ketone with lithiated 2-m…     

Chiral Imidazoline Ligands and Their Applications in Metal-Catalyzed Asymmetric Synthesis

As a structural analog of oxazoline,imidazoline(4,5-dihydroimidazole)has received much attention in the rational design of chiral ligands.The additional N-substituent provides broader space for fine-tuning of electronic and steric effects,and it offers a good handle for immobilizing onto solid supports.In the past decades,imidazoline ring has emerged as a powerful candidate for the design of chiral nitrogen-containing ligands,as well as a significant alternative for oxazoline ring.Various chiral imidazoline ligands have been designed and utilized in asymmetric organic reactions.These new catalysts can not only be applied in classical reactions,but also be employed to develop new organic reactions with high enantioselectivities.This review provides an overview of chiral imidazoline ligands.Their applications in asymmetric synthesis are also summarized.     

Supramolecular Assemblies of (±-2,2''''-Dihydroxy-1,1''''-binaphthyl with 2,2''''-Bipyridine and Naphthodiazine

Introduction Optically active 1,1'-bi-2-naphthol (BINOL) and its derivatives have been widely used as chiral ligands of catalysts for asymmetric reactions and effective host compounds for the isolation or optical resolution of a wide range of organic guest molecules through the for-mation of crystalline inclusion complexes.1,2 The wide-ranging and important applications of these com-pounds in organic synthesis have stimulated great inter-est in developing efficient methods for their prepara-…     

Synthesis of (s)-(-)-Benzyl-2-tert-butoxycarbonyl amino-4-iodobutyrate

The proteinogenic (-amino acids constitute an important section of the "chiral pool", being inexpensive in the L-form (but available if necessary as the D enantiomers), structurally varied and chemically versatile1, they are useful starting materials for chiral reagents, auxiliaries and ligands2. Any high-yielding transformation of an (-amino acids which proceeds without racemization is thus of potential importance, especially if it generates another reactive center and may be applied to the s…     

Synthesis of Chiral N-Ferrocenylmethylaminoalcohols and their Application in Enantioselective Addition of Diethylzinc to Aldehydes

Three chiral N-ferrocenylmethylaminoalcohols were synthesized from readily available natural L-valine, leucine and phenylanine, and used as chiral ligands in the enantioselective addition of diethylzinc to aldehydes.     

Synthesis of Novel Chiral Dibenzo [ a, c ] cycloheptadiene Bis(oxazoline) and Catalytic Asymmetric Reactions

Over the last decade, C2-symmetric chiral oxazoline metal complexes have been recognized as an effective classof chiral catalyst in a variety of transition metal catalyzed asymmetric reactions. [1] High catalytic activities and enantiomeric excesses have been obtained using C2-symmetric chiral ligands in conjunction with suitable transition metal ion, for example, the hydrosilylation of ketone, allylic alkylation, Michael addition, Diels-Alder cycloaddition, and cyclopropanation. Thus, the design and synthesis of new chiral oxazoline ligands have inspired many scientists to work with great efforts.     

NMR Studies of 3-Acylcamphor

6-Diketones are useful chelating agents with many metal ions. Chiral 6-diketones.especially chiral 3-acylcamphors as an outstanding representation, have even moreextensive applications as stationary phases in chromatograpy and as ligands of chemicalshifting reagents in NMR spectroscopy'for determining the enantiomeric excess of 'chrialcompoundsl=. Furthermore, they can be 'used as ligands in asymmetric catalysis'-'.Much work has been done for the synthesis of 3-acylcamphors due to their broad…     

A Novel Bimetallic Tetrahedron Cobalt Complex Promoting the Addition of Diethylzinc to Benzaldehyde

Asymmetric catalytic addition of dialkyzinc to aldehyde using chiral ligands has become one of the most active areas in asymmetric synthesis. In recent years, various chiral ligands have exhibited good results in promoting this asymmetric addition1, such asβ- amino alcohol and chiral amine which possess chiral carbon centers, chiral ((6-arene) chromium complexes2, derivatives of Ferrocene3, which possess planar chirality, and BINOL and NOBIN4. Further development of novel catalysts is sti…     

Enantiomeric Separation of Amino Alcohols by Ion-pair Chromatography

Many drugs or physiologically important compounds are chiral molecules and the optical isomers of them may differ in their pharmacological activities. In some instances differences in undesirable side-effects of these enantiomers are important. So the separation of chiral compounds is becoming increasingly important. Liquid chromatography (LC) is well known as an excellent method for separating and analyzing mixtures of stereoisomers. For resolving the ionic chiral compounds it is available t…     

Enantioselective Synthesis of Chiral 1-Ferrocenyl Alcohol via CBS-Reduction

In recent years present interest in the synthesis of chiral ligands has directed attention to the preparation of optically active compounds bearing a ferrocenyl or other organometallic group at the alpha carbon atom. The chirality of all the optically active ferrocenes is due to the ferrocene planar chirality. And many chiral phosphines or amines bearing a ferrocene unit have been used as ligands for transition metal catalyzed asymmetric transportations1. These complexes have been convenien…     

Synthesis and Crystal Structure of the Novel Chiral o—Hydroxyphenyloxazoline Metal Complexes

1 INTRODUCTION Optically active oxazolines have been extensi- vely used as valuable chiral ligands for transition metals in asymmetric catalysis[1]. The design and syntheses of new chiral oxazoline ligands have inspired many scientists to work with great efforts during the recent years. Our interest has been focus- ed on the studies of enantioselective transition- metal catalysis of heterocyclic ligands. In the pre- sent work, we choose o-hydroxyphenyloxazoline ligand for it has a rigi…     

Spontaneous resolution and absolute chiral induction of 3d-4f heterometal-organic frameworks from achiral precursors

The asymmetric assembly and spontaneous resolution of chiral heterometal-organic frameworks from achiral precursors remain a great challenge. Herein, we report the formation and spontaneous resolution of three-dimensional(3 D) chiral 3 d-4 f heterometal-organic frameworks from achiral ligands in the presence of lactic acid enantiomers as chiral inducers. In the absence of a chiral inducer, the reactants randomly generated both enantiopure crystals in equal measure. However, enantiopure lactic acid induced asymmetric resolution to achieve single chiral crystallization. DFT theoretical calculations showed that the absolute chiral resolution of the enantiomers is due to the difference in the interactions between the two enantiomeric Λ/Δ-[Fe L3]3-units and the chiral inducer.     

Synthesis of New Chiral Phosphine Ligands and Their Application in Asymmetric Hydrogenation of Ketones

The design of new chiral ligands is the key in the development of transition metal catalyzed asymmetric synthesis. Many chiral diphosphine ligands have been prepared and applied in asymmetric catalytic reactions with excellent enantioselectivities. Among the chiral diphosphine ligands that have been reported, the atropisomeric C2-symmetric phosphines with a biaryl scaffold initiated by Noyori and co-workers with BINAP were found to have the widest application in the transition metal catalyze…     

Using Natural Cinchona Alkaloids to Promote the Enantioselective Addition of Dialkylzinc to N－Diphenylphosphinylimines

Cinchona alkaloids are utilized as chiral ligands to promote the enantioselective addition of dialkylzinc to N-diphenyiphosphinylirnlnes affording enantiomerically enriched N-diphenyiphosphinylamines in up to 91% ee.     

Asymmetric Synthesis of Anisodine

Anisodine was synthesized from 3α-hydroxy-6β-acetyltropine in 11 steps. Laevorotary isomer of anisodine was prepared from the asymmetric dihydroxylation of compound 10 via the osmium catalyzed process employing p-chlorobenzoyl dihydroquinidine as the chiral ligands.     

Asymmetric Diels—Alder Reaction Catalyzed by Novel Chiral Dibenzo[a,c] cycloheptadiene Bis（oxazoline） Metal Complexes

A series of novel chiral C2-symmetric bis (oxazoline) ligands have been synthesized.The copper and magnesium complexes,prepared in situ from copper(Ⅱ)-triflate of magnesium triflate with the new enantiopure oxazoline ligands,were evaluated as chiral catalysts in the enantioselective Diels-Alder reaction of cyclopentadiene with N-crotenoyl-oxazolidin-2-one.Primary results showed that diastereoselectivity up to 94% and enantioselectivity up to 68% ee for endo products were observed respectively with these ligands.     

Highly Enantioselective Diels-Alder Reactions Promoted by Non C2-Symmetric Chiral Ligands

Ligand design and synthesis occupy a central theme in asymmetric catalysis. [1] In developing chiral ligands, their design should provide an opportunity for tuning through easy modification of substituents. In a large number of cases, this means starting from a new chiral source. We have been interested in design/synthesis of novel chiral ligands that allow for diversity to be introduced with ease. We have designed a new ligand system containing a core dihydropyrazole moiety with chiraliuy residing remotely to the fluxional group as shown in Scheme 1. There are three points of diversity and these are indicated on the structure.