New chiral diphosphoramidite rhodium(I) complexes for asymmetric hydrogenation

Chiral 1,5‐cyclooctadiene rhodium(I) cationic complexes with C₂‐symmetric chelate diphosphoramidite ligands containing (R,R)‐1,2‐diaminocyclohexane as the backbone and two atropoisomeric biaryl units were easily synthesized and fully characterized by multinuclear one‐ and two‐dimensional NMR spectroscopy and elemental analysis. These complexes were used as catalysts in the asymmetric hydrogenation of dimethyl itaconate, methyl 2‐acetamidoacrylate and (Z)‐methyl‐2‐acetamido‐3‐phenylacrylate. The rhodium complexes derived from diphosphoramidite ligands that contain two (R) or (S) BINOL (2,2′‐dihydroxy‐1,1′‐binaphthyl) units proved to be efficient catalysts, giving complete conversion and very good enantioselectivity (up to 88% ee). An uncommon positive H₂ pressure effect on the enantioselectivity was observed in the hydrogenation of dimethyl itaconate catalyzed by Rh‐complex with diphosphoramidite ligand that contains two (S)‐binaphthol moieties. Copyright © 2014 John Wiley & Sons, Ltd.     

New amidophosphine-phosphinites (tLANOPs) as chiral ligands for asymmetric hydrogenation reactions

The new amidophosphine-phosphinite (AMPP) ligands 4a–g (called tLANOP ligands) derived from the chiral hydroxy amide (R)- or (S)-2-hydroxy-3,3,N-trimethylbutyramide have been prepared in 48–83% yield. The crystal structures of the square planar complexes [(SP-4-3)-Pd((R)-dmphea)((S)-4a)]BF₄ and [Rh((R)-4a)(COD)]BF₄ have allowed the absolute configurations of the ligands to be assigned. In both complexes the 7-membered chelating ring of 4a has virtually the same twist-boat conformation. With this class of ligands the rhodium catalyzed asymmetric hydrogenation of 4-oxoisophorone enol acetate gave (S)-phorenol acetate in up to 71% ee. The iridium catalyzed asymmetric hydrogenation of the cyclic iminium salts 16a and 16b afforded after work-up the corresponding cyclic secondary amine (S)-17 in up to 86% ee, when bulky groups were present on the phenyl substituents on the two phosphorus atoms.     

New chiral (salen)manganese(III) systems for asymmetric epoxidation of styrene

Highly enantioselelctive and repeatable epoxidation of styrene was performed by using new chiral (salen)Mn(III) catalysts, which were derived from the initial immobilization of a homogeneous (salen)Mn(III) complex on solid carriers and subsequent dispersion into ionic liquids. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Palladium-catalyzed asymmetric tandem allylic substitution using chiral 2-(phosphinophenyl)pyridine ligand

Palladium-catalyzed asymmetric tandem allylic substitution of (Z)-1,4-diacyloxy- and (Z)-1,4-bis(alkoxycarbonyloxy)-2-butene (2a-c) using 2-(phosphinophenyl)pyridine 1 as chiral ligand provided optically active six-membered 2-vinyl-1,4-diheterocyclic compounds with good to high enantioselectivity. For example, the reactions with catechol, 2-(benzylamino)phenol, or 1,2-bis(benzylamino)ethane as a nucleophile gave 2-vinyl-1,4-benzodioxane (71% ee), 4-benzyl-2-vinyl-1,4-benzoxazine (86% ee), and 1,4-dibenzyl-2-vinylpiperazine (86% ee), respectively.     

Chirality and asymmetric transformations of axially chiral 4,5-disubstituted phenanthreneamides

We have investigated the rotation barriers of 4-carbamoylphenanthrene and 4-thiocarbamoylphenanthrene and the asymmetric transformations of the novel 4-carboxy-5-carbamoylphenanthrenes. The similar ArC and CN barriers of 92 kJ/mol of 4-carbamoylphenanthrene indicate a strongly correlated process of both rotations. Only the corresponding thioamide could be separated on microcrystalline triacetylcellulose and a barrier of 115.6 kJ/mol was obtained from thermal racemization. Despite the large steric hindrance of the tightly interlocked substituents of the 4-carboxy-5-carbamoylphenanthrenes, the chirality became visible only at temperatures below −60°C by ¹H NMR spectroscopy. Only six of the eight possible stereoisomers, which may form four racemates, have been observed, namely two anti and one syn species. After the asymmetric transformation, one further syn arrangement is less populated or does not exist and the two anti isomers exist in an unequal ratio. Two orientations were found for the amide group: a major form A with the Me^E ‘outside’ and the carbonyl group ‘inside’ the bay-area and a minor form B with the reverse arrangement. The low barriers of 4-carboxy-5-carbamoylphenanthrenes indicate that steric hindrance and electrostatic repulsion in the transition state are compensated by correlated ArC and CN rotations and by twisting the phenanthrene plane. In the transition state, the carbonyl group passes the bay area and the pyramidal amide group passes H³ or H⁶ of the phenanthrene ring.     

Aza-bis(oxazolines): new chiral ligands for asymmetric catalysis

Aza-bis(oxazolines) are introduced as chiral ligands for asymmetric catalysis combining the advantages of easy availability of bis(oxazolines) and backbone variability of aza-semicorrins. Especially, the title ligands could be attached to a polymeric support, which allowed the development of easily recoverable copper(I)-catalysts for asymmetric cyclopropanation reactions.     

5,5-Dimethyl-2-phenylamino-2-oxazoline as an effective chiral auxiliary for asymmetric alkylations

The novel chiral auxiliaries, 5,5-diphenyl-2-phenylamino-2-oxazoline and 5,5-dimethyl-2-phenylamino-2-oxazoline, were prepared from l-valine methyl ester. The 5,5-dimethyl compound was shown to be a particularly effective chiral auxiliary for asymmetric alkylation affording high yields and diastereoselectivities.     

New 2-azanorbornyl derivatives: chiral (N,N)-donating ligands for asymmetric catalysis

New chiral 2-azanorbornane derivatives were prepared and used as (N,N)-donating ligands in a copper-catalyzed Henry reaction yielding up to 62% ee.     

Axially chiral electron-rich TunePhos-type ligand: synthesis and applications in asymmetric hydrogenation

A new electron-rich TunePhos type ligand has been synthesized; excellent enantioselectivities (up to 99% ee) have been achieved in Rh-catalyzed asymmetric hydrogenation of α-dehydroamino acid methyl esters and dimethyl itaconate.     

A new chiral sulfinyl-NH-pyridine ligand for Ir-catalyzed asymmetric transfer hydrogenation reaction

A new flexible C₁-symmetric tridentate ligand (S)-N-(2-(tert-butylsulfinyl)benzyl)-1-(pyridin-2-yl)methanamine sulfoxide (L1) was successfully prepared and utilized as a chiral ligand for Ir(I)-catalyzed ATH (asymmetric transfer hydrogenation) reactions. Without any cooperation of other chiral center, encouraging ee and conversion values have been achieved, which provide us a better understanding on these types of ligands and a new strategy to develop new high-efficiency chiral catalysts for asymmetric reaction.     

Optically active 1,2-bis(1-arylhydroxymethyl) ferrocene: a new, efficient chiral ligand for scandium-catalyzed asymmetric Diels-Alder reaction

[reaction: see text] The Sc(OTf)3/FERRODIOL (2) complex was prepared at -78 degrees C in CH2Cl2 in the presence of 2,6-lutidine and MS 4A. The chiral scandium Lewis acid-catalyzed asymmetric Diels-Alder reaction of cyclopentadiene (3) with 3-acyloxazolidin-2-ones (4) effectively produced the adduct (5) in a high yield with good selectivity, i.e., endo/exo = 90:10 up to 91% ee (endo).     

Highly effective chiral phosphorus amidite-olefin ligands for palladium-catalyzed asymmetric allylic substitutions

This paper describes the development of a type of novel P-olefin hybrid ligand by the incorporation of terminal olefins onto phosphorus amidite ligands for palladium-catalyzed asymmetric allylic alkylations of indoles and substitutions with amines to give the desired products in 70-97% yield with 91-98% ee.     

New monodentate chiral phosphite ligands for asymmetric hydrogenation

We report the synthesis of new chiral monodentate phosphite ligands with a biphenyl backbone, the axial chirality of which is introduced early in the synthesis and locked by a chiral alkylenedioxy bridge. We also describe results obtained with these ligands in rhodium-catalysed asymmetric hydrogenation of various substrates.     

New camphor derived chiral ligands for asymmetric synthesis

New enantiomerically pure 1,4-diols and 1,4-aminoalcohols have efficiently been prepared in one and two steps, respectively, from a commercially available camphor derived exo fused lactone. Using sterically hindered amines, an aldol addition of two lactone molecules was observed and the stereochemistry of the products was determined by X-ray crystallography.     

New chiral auxiliaries for highly stereoselective asymmetric methoxyselenenylations

Replacement of the 2-keto group of readily available di(endo-3-camphoryl) diselenide with oxime or O-benzoyloxime substituents, followed by conversion into the corresponding selenenyl triflates, produced highly effective chiral selenium electrophiles for the asymmetric oxyselenenylation of alkenes in the presence of methanol.     

SimplePHOX, a readily available chiral ligand system for iridium-catalyzed asymmetric hydrogenation

[reaction: see text] New Ir-SimplePHOX complexes Ir-6-Ir-9 catalyze the quantitative, highly enantioselective hydrogenation of a range of unfunctionalized and functionalized olefins. Synthesis, catalytic results, and X-ray crystal structures are presented here.