A New Chiral Director for the Highly Diastereoselective Borane Reductionof Steroid-20-ones

Summary.  The synthesis of a new chiral boroxazolidine was achieved which was used to control the stereochemistry of the borane reduction of the 20-keto group of steroids. The otherwise hardly accessible 20α-(20S)-alcohol can thus be prepared in a yield of 91%. Received April 10, 2000. Accepted (revised) May 2, 2000     

A New Chiral Catalyst for the Enantioselective Reduction of Prochiral Ketones with Borane

A new chiral β-amino alcohol, (s)-2-amino-1, 1-diphenyl-3-(2-naphthyl)-1-propanol and its use as a catalyst in the enantioselective reduction of prochiral ketones with borane were described.     

A Continuously Regenerable Chiral Ammonia Borane for Asymmetric Transfer Hydrogenations

A novel chiral ammonia borane was designed and developed through the dehydrogenation of ammonia borane with a chiral phosphoric acid, which was highly effective for the asymmetric transfer hydrogenation of imines and β‐enamino esters to afford high levels of reactivities and enantioselectivities. Significantly, this chiral ammonia borane can be continuously regenerated during the transfer hydrogenation with the assistance of water and ammonia borane, which made it possible to obtain satisfactory results using only 0.1 mol % of the chiral phosphoric acid. Notably, the role of chiral phosphoric acid is to produce the chiral ammonia borane.     

Simple and Efficient Procedure for Highly Diastereoselective Synthesis of trans- 1,1-Disubstituted-2,6-diarylcyclohexane-4-ones

A simple and efficient method has been developed for highly diastcreoselective synthesis of trans-1,1-disubstituted-2,6-diarylcyclohexane-4-ones from dibenzalacetone and malononitril with trans-1,2-diaminocyclohexane as catalyst. The substrate 1,5-diaryl-1,4-pentadien-3-ones and active methylene compounds proceeded to give the products with good to excellent yield within a short time.     

Highly Enantio- and Diastereoselective Hetero-Diels–Alder Reactions Catalyzed by New Chiral Tridentate Chromium(III) Catalysts

Even moderately nucleophilic dienes react with simple aldehydes in the presence of a new Cr^III catalyst in a hetero-Diels–Alder reaction [Eq. (1)]. Tetrahydropyranyl products with up to three stereogenic centers are generated in near-perfect diastereoselectivities and with greater than 90 % ee (99 % ee for the example shown). TBAF=tetrabutylammonium fluoride; TBS=tert-butyldimethylsilyl; TES=triethylsilyl.     

A Simple Diastereoselective Synthesis of Chiral Nonracemic Aliphatic Amines

An efficient procedure has been developed for the diastereoselective synthesis of chiral aliphatic amines (diastereoisomeric excess >96%) from (1S)-N-(1-methylethylidene)-1-phenylethylamine, i.e., Schiff base derived from the simplest ketone (acetone) and (1S)-1-phenylethylamine. The procedure includes successive lithiation, alkylation, and reduction and is characterized by high regioselectivity in the formation of alkylated syn-Z-imines. Hydride reduction of the prochiral C=N bond in the latter gives mainly optically active aliphatic amines with R configuration. All reactions are performed as a one-pot process without isolation of intermediate products.__________Translated from Zhurnal Organicheskoi Khimii, Vol. 41, No. 6, 2005, pp. 827–831.Original Russian Text Copyright © 2005 by Grishina, Luk’yanenko, Borisenko.     

Non-cross-linked Polystyrene Supported Cyclosulfamide:A New Chiral Auxiliary for Highly Stereoselective Alkylation Reactions

The asymmetric alkylation reactions induced by non-cross-linked polystyrene supported cyclosulfamide chiral auxiliary occurred in moderate to good yields with a very high stereoselectivity（e.e.〉99%）. Compared to non-supported cyclosulfamide chiral auxiliary, this chiral auxiliary can be recovered by simple precipitation and filtration, and could be reused at least four cycles without appreciable reduction in the yield or stereoselectivity.     

A New Chiral Binaphthalene‐Based Fluorescence Polymer Sensor for the Highly Enantioselective Recognition of Phenylalaninol

A new (S)‐binaphthalene‐based polymer ( P ‐ 1 ) was synthesized by the polymerization of 5,5′‐((2,5‐dibutoxy‐1,4‐phenylene)bis(ethyne‐2,1‐diyl))bis(2‐hydroxy‐3‐(piperidin‐1‐ylmethyl) benzaldehyde ( M ‐ 1 ) with (S)‐2,2′‐dimethoxy‐(1,1′‐binaphthalene)‐3,3′‐diamine ( M ‐ 2 ) through the formation of a Schiff base; the corresponding chiral polymer ( P ‐ 2 ) could be obtained by the reduction of polymer P ‐ 1 with NaBH₄. Chiral polymer P ‐ 1 exhibited a remarkable “turn‐on” fluorescence‐enhancement response towards (D )‐phenylalaninol and excellent enantioselective recognition behavior with enantiomeric fluorescence difference ratios (ef) as high as 8.99. More importantly, chiral polymer P ‐ 1 displays a bright blue fluorescence color change upon the addition of (D )‐phenylalaninol under a commercially available UV lamp, which can be clearly observed by the naked eye. On the contrary, chiral polymer P ‐ 2 showed weaker enantioselective fluorescence ability towards the enantiomers of phenylalaninol.     

Chiral-at-Iron Catalyst for Highly Enantioselective and Diastereoselective Hetero-Diels-Alder Reaction

This study demonstrates that chiral-at-iron complexes, in which all coordinated ligands are achiral and the overall chirality the consequence of a stereogenic iron center, are capable of catalyzing asymmetric transformations with very high enantioselectivities. The catalyst is based on a previously reported design (J. Am. Chem. Soc. 2017 , 139, 4322), in which iron(II) is surrounded by two configurationally inert achiral bidentate N-(2-pyridyl)-substituted N-heterocyclic carbenes in a C₂-symmetric fashion and complemented by two labile acetonitriles. By replacing mesityl with more bulky 2,6-diisopropylphenyl substituents at the NHC ligands, the steric hindrance at the catalytic site was increased, thereby providing a markedly improved asymmetric induction. The new chiral-at-iron catalyst was applied to the inverse electron demand hetero-Diels-Alder reaction between β,γ-unsaturated α-ketoester and enol ethers provide 3,4-dihydro-2H-pyrans in high yields with excellent diastereoselectivities (up to 99 : 1 dr) and excellent enantioselectivities (up to 98 % ee). Other electron rich dienophiles are also suitable as demonstrated for a reaction with a vinyl azide.     

测定手性有机酸对映体纯度的新试剂

用NMR技术测定微量手性化合物的对映体纯度,已有多种方法。其中,加手性镧化物位移试剂法适用面最广,但对有机酸,结果常不理想。另一种使用较广的方法是加手性试剂,将样品中两对映体转变成非对映异构体,然后比较非对映基因NMR信号的强度,确定原样品中对映体的组成比例。国外已出售的手性试     

手性噁唑硼烷结构与还原苯基乙基甲酮的对映选择性研究~≠

本文以苯基乙基甲酮为还原底物,研究了原地(in situ)制备的在3、4、5位具有不同取代基的手性1,3,2-(口恶)唑硼烷催化剂的结构与不对称催化效应关系。研究结果表明,在不对称催化硼烷还原反应中(CBS方法),产物的构型和对映选择性主要受手性(口恶)唑硼烷的4位取代基控制。     

Bis(O-nitrophenyl) Carbonate as a New Reagent for the Synthesis of Chiral Oxazolidin-2-ones

Bis(o-nitrophenyl) carbonate reacts under mild conditions with chirals 1,2-amino alcohols and, after addition of DMAP, affords the corresponding oxazolidin-2-ones in very good yields.     

Diastereoselective Cyclopropanation Utilizing a New Chiral N,O-Acetals Prepared by Electrochemical Oxidation of Carbamates

A new chiral bicyclic tetrahydropyridine derivative was synthesized from L -lysine derivatives utilizing electrochemical oxidation as a key step. Allyl alcohols were incorporated into the tetrahydropyridine derivative to afford N,O-acetals, and the reaction of the resulting N,O-acetals with a carbenoid, which was generated from Et₂Zn and CH₂l₂, yielded cyclopropanated products in moderate diastereoselectivities.     

Diastereoselective Alkene Hydroesterification Enabling the Synthesis of Chiral Fused Bicyclic Lactones

Palladium-catalysed diastereoselective hydroesterification of alkenes assisted by the coordinative hydroxyl group in the substrate afforded a variety of chiral γ-butyrolactones bearing two stereocenters. Employing the carbonylation-lactonization products as the key intermediates, the route from the alkenes with single chiral center to chiral THF-fused bicyclic γ-lactones containing three stereocenters was developed.     

Single-Layered Chiral Nanosheets with Dual Chiral Void Spaces for Highly Efficient Enantiomer Absorption

Although considerable effort in recent years has been devoted to the development of two-dimensional nanostructures, single-layered chiral sheet structures with a lateral assembly of discrete clusters remain elusive. Here, we report single-layered chiral 2D sheet structures with dual chiral void spaces in which discrete clusters of planar aromatic segments are arranged with in-plane AB order in aqueous methanol solution. The chirality of the sheet is induced by the slipped-cofacial stacks of rectangular plate-like aromatic segments in the discrete clusters which are arranged laterally with up and down packing, resulting in dual chiral void spaces. The chiral nanosheets function as superfast enantiomer separation nanomaterials, which rapidly absorb a single enantiomer from a racemic mixture with greater than 99 % ee.