Stereoselective polymerization of racemic lactide (rac-LA) was examined using Al-achiral ligand complexes. By introduction substituents in aromatic rings Schiff base ligands, a higher selectivity obtained without any chiral auxiliaries the catalyst via chain-end control mechanism. The T(m) values (T(m) 170-192 degrees C) were comparable to or than that homochiral polymer, poly(L-LA) 162 C), and thermally more stable polylactide prepared from rac-LA.

Electron-donating group-substituted 2-iodoxybenzoic acids (IBXs) such as 5-Me-IBX (1g), 5-MeO-IBX (1h), and 4,5-Me2-IBX (1i) were superior to IBX 1a catalysts for the oxidation of alcohols with Oxone (a trademark DuPont) under nonaqueous conditions, although was almost insoluble in most organic solvents. The catalytic proceeded more rapidly cleanly nitromethane. Furthermore, 2-iodoxybenzenesulfonic acid (IBS, 6a) much active than modified IBXs. Thus, we established a highly efficient...

The 1,2-diamine (vicinal diamine) motif is present in a number of natural products with interesting biological activity and many chiral molecular catalysts. efficient stereocontrolled synthesis enantioenriched vicinal diamines still challenge to modern chemical methodology. We report here both syn- anti-selective asymmetric direct Mannich reactions N-protected aminoacetaldehydes N-Boc-protected imines catalyzed by proline the axially amino sulfonamide (S)-3. This organocatalytic process...

BBr3-chiral phosphoric acid complexes are highly effective and practical Lewis acid-assisted Brønsted (LBA) catalysts for promoting the enantioselective Diels-Alder (DA) reaction of α-substituted acroleins α-CF3 acrylate. In particular, DA with 1,2-dihydropyridines gave corresponding optically active isoquinuclidines high enantioselectivities. Moreover, transformations to key intermediates indole alkaloids, catharanthine allocatharanthine, demonstrated.

Pick and choose: The asymmetric synthesis of two different enantiomeric products has been achieved through the use a single organocatalyst with or without achiral organic acid additives (see scheme). These may assist in altering substrate orientations at catalytic center, leading to efficient inversions both aldol Mannich products. Detailed facts importance specialist readers are published as "Supporting Information". Such documents peer-reviewed, but not copy-edited typeset. They made...

This communication describes the rational design of an l-histidine-derived minimal artificial acylase. Our new acylase, tert-butyldiphenylsilyl ether N-(2,4,6-triisopropylbenzenesulfonyl)-pi(Me)-l-histidinol, is a simple and small molecule (molecular weight = 660) that contains only one chiral carbon center originates from natural l-histidine. The kinetic acylation racemic secondary alcohols induced by this compound showed S (kfast/kslow) value up to 93. A reusable polystyrene-bound acylase...

We have designed a minimal artificial metalloenzyme that is prepared in situ from Cu(OTf) 2 or Cu(NTf 2) (1.0 equiv) and L-DOPA-derived monopeptide (1.1 based on the cation-pi attractive interaction between copper(II) aromatic arm of ligand, which postulated basis X-ray diffraction analysis theoretical calculations. This catalyst (2-10 mol %) highly effective for not only enantioselective Diels-Alder reaction with alpha,beta-unsaturated 1-acyl-3,5-dimethylpyrazoles but also Mukaiyama-Michael...

The Mukaiyama cross-aldol reaction of α-fluoro-, α-chloro-, and α-bromoacetaldehyde-derived (Z)-tris(trimethylsilyl)silyl enol ethers is described, furnishing anti-β-siloxy-α-haloaldehydes. A highly diastereoselective, one-pot, sequential double-aldol process developed, affording novel β,δ-bissiloxy-α,γ-bishaloaldehydes. Reactions are catalyzed by C(6)F(5)CHTf(2) C(6)F(5)CTf(2)AlMe(2) (0.5-1.5 mol %) provide access to halogenated polyketide fragments.

The rational design of bis(oxazoline)-copper(II) catalysts based on postulated intramolecular secondary n-cation interaction for the highly enantioselective Diels-Alder reaction is presented. A theoretical calculation suggested that n electrons 4,4'-sulfonamidomethyl groups successfully interact with Cu(II) cation and counteranions protons sulfonamido groups. These interactions might be essential high catalytic activity, broad range substrates, level induction enantioselectivity.

Swapped selectivities: The use of tailor-made catalysts results in anomalous endo/exo selectivities and high enantioselectivities the Diels–Alder reactions cyclopentadiene with different acroleins (see scheme). These supramolecular are prepared situ from chiral diols, arylboronic acid, tris(pentafluorophenyl)borane, can discriminate re/si face dienophile as well approach diene. Detailed facts importance to specialist readers published "Supporting Information". Such documents peer-reviewed,...

Brønsted base-assisted boronic acid catalysis for the dehydrative self-condensation of carboxylic acids is described. Arylboronic bearing bulky (N,N-dialkylamino)methyl groups at 2,6-positions can catalyze intramolecular condensation di- and tetracarboxylic acids. This first successful method catalytic

Catalytic and highly enantioselective Diels−Alder reaction of cyclic acyclic dienes with α-phthalimidoacroleins provides α-quaternary α-amino acid precursors. The conformationally flexible chiral ammonium salt H-l-Phe-l-Leu-N(CH2CH2)2-reduced triamine pentafluorobenzensulfonic is very effective as an asymmetric catalyst for the reaction.

Teaming up to make it happen: In the title reaction, Lewis basic site of catalyst activated ethyl cyanoformate, and deep flexible Brønsted acidic cavity stabilized selectively recognized key reaction intermediate promote asymmetric acylation (see scheme). As a service our authors readers, this journal provides supporting information supplied by authors. Such materials are peer reviewed may be re-organized for online delivery, but not copy-edited or typeset. Technical support issues arising...

A new chiral tethered 8-quinolinol-based ligand class is developed. The binuclear titanium complex of the operates through a novel mechanism allowing for regio- and stereoselective epoxidation primary tertiary homoallylic alcohols (up to 98% ee), as well first examples 2-allylic phenols 92% ee). catalyst system also promotes asymmetric oxidation γ-hydroxypropyl sulfides giving an important sulfoxides that have been inaccessible date 95%

Ketone super silyl enol ethers are shown to be excellent nucleophiles in the Mukaiyama aldol reaction as well sequential one-pot diastereoselective reactions. High yields and diastereoselectivities obtained with a variety of ether/aldehyde/Grignard combinations. The utility this is exemplified 4-component generating two secondary one tertiary alcohol step.

Di-tert-butyl methylenemalonate (1) could be employed as a reactive equivalent of three-carbon Michael acceptor such acrylate in direct asymmetric conjugate addition aldehydes catalyzed by an axially chiral amino diol (S)-3a. Furthermore, acrylate, unexplored and challenging substrate enamine catalysis, has also been successfully reaction. Relatively inert is doubly activated polyfluoroalkyl group 2 the hydroxyl on catalyst (S)-3b, giving corresponding adducts high yield with excellent...

The aldol addition of methyl ketones to β-siloxy and α-methyl aldehydes is described. Careful control mechanistically distinct reactions leverages 1,2- 1,3-asymmetric induction, selectively forming syn anti adducts with excellent diastereocontrol. Experimental theoretical investigations have provided insight the factors governing diastereoselectivity.

Oil-soluble N,N-diarylammonium pyrosulfates as nonsurfactant-type catalysts for the dehydrative ester condensation under aqueous conditions are described. Preheat treatment of dibasic sulfuric acid with bulky N,N-diarylamines generates water-tolerant salts pyrosulfuric active catalyst species. The present in water can also widely be applied to unusual selective esterifications and glycosylation.

Bifunctional Brønsted base-assisted boronic acid catalysts, arylboronic acids bearing two sterically bulky (N,N-dialkylamino)methyl groups at the 2,6-positions, exhibit remarkable activities for dehydrative intramolecular condensation of dicarboxylic acids. The steric bulkiness 1, which prevents formation less active species such as N→B chelated and triarylboroxines 3, is crucial high catalytic activity. This first successful method self-condensation di- tetracarboxylic

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTAsymmetric Diels-Alder Reaction of Unsymmetrical Maleates. A Chemical Access to Chiral, cis-Cyclohexene-1,2-dicarboxylatesKeiji Maruoka, Matsujiro Akakura, Susumu Saito, Takashi Ooi, and Hisashi YamamotoCite this: J. Am. Chem. Soc. 1994, 116, 14, 6153–6158Publication Date (Print):July 1, 1994Publication History Published online1 May 2002Published inissue 1 July...

An enantioselective Diels–Alder reaction of 1,2-dihydropyridines with α-acyloxyacroleins catalyzed by a chiral primary ammonium salt has been developed.

ABSTRACT Nucleophilic phosphite–urea cooperative catalysts are highly efficient for the bromonium‐induced cyclization of 2‐geranylphenols. Phosphite– N,N ’‐dimethylurea also show moderate activity, probably due to steric effect their bent conformation. Chirality 26:355–359, 2014. © 2014 Wiley Periodicals, Inc.

Silyl superpowers: The supersilyl group was investigated as a superior carboxylic acid protecting group. Supersilyl esters were also utilized stable synthetic equivalents in highly stereoselective aldol and Mannich reactions (see scheme). value of this method lies easy photodeprotection the rapid synthesis polyketide subunits.