Enantioselective Hydrogenation of α-Substituted Acrylic Acids Catalyzed by Iridium Complexes with Chiral Spiro Aminophosphine Ligands

Highly active: Iridium complexes with chiral spiro aminophosphine ligands were synthesized and applied as catalysts for the asymmetric hydrogenation of α-substituted acrylic acids. The complexes were highly active catalysts, showing turnover frequencies of up to 6000?h(-1) , and catalyst loadings could be reduced to 0.01?mol?%.     

Enantio- and Diastereoselective Oxidation of N-Alkylimines Using Chiral α-Bromonitriles and Hydrogen Peroxide System

Chiral α-bromonitriles were prepared with good chemical and optical yields starting from natural α-amino acids by dehydrating the corresponding α-bromoamides with thionyl chloride. The combined system α-bromonitriles/hydrogen peroxide was examined for the enantio- and diastereoselective oxidation of N-alkylimines in basic media at room temperature. The oxidation of N-tertiobutylarylimines leads to optically active oxaziridines with moderate enantiomeric excess. However, the oxidation of (S)-1-phenylethylarylimines affords the corresponding oxaziridines with good diasteromeric excess up to 97/3 as proved by gaseous-phase chromatography.     

Selective Hydrogenation of Avermectin Catalyzed by Iridium-Phosphine Complexes

A series of new iridium complexes, IrCl（COD）（TMOPP） （1） [COD=1,5-cyclooctadiene, TMOPP=tris（4- methoxyphenyl）phosphine], IrCl（COD）（TFMPP） （2） [TFMPP = tris（4-trifluoromethylphenyl）phosphine], IrCl（COD）（BDNA） （3） [BDNA= 1,8-bis（diphenylphosphinomethyl）naphthalene], IrCl（COD）（BISBI） （4） [BISBI= 2,2＇-bis（diphenylphosphinomethyl）biphenyl] and IrCl（COD）（BDPB） （5） [BDPB= 1,2-bis（diphenylphosphinomethyl）benzene], were synthesized and characterized by NMR spectra and elemental analyses. In order to obtain the relationships between complex structures and their catalytic properties, IrCl（COD）（DPPM） （6） [DPPM = bis（diphenylphosphino）methane], IrCl（COD）（DPPE） （7） [DPPE= 1,2-bis（diphenylphosphino）ethane], IrCl（COD）（DPPP） （8） [DPPP=1,3-bis（diphenylphosphino）propane] and IrCl（COD）（TPP） （9） [TPP=triphenylphosphine], were also synthesized according to the reported methods. The hydrogenation results showed that the low electronic density at the central metal was favorable to increase the catalytic activity for the hydrogenation of avermectin, but decrease the selectivity to ivermectin. The complex with a large chelating ring and a bulky chelating backbone would easily cause the cleavage of C-O bond in avermectin to give a byproduct avermectin aglycon.     

The Activation and Carbonylation of the C-Cl Bond Catalyzed by Transition-Metal Complexes

Thecarbonylationoforganichalides,catalyzedbytransition-metalcomPlexes,isareactionofindustrialinterestleadingtoawiderange0fproductslilieesters,aldehydes,awhdesandacids.Formanyyears,catalyticactivationandfunctionalisationofthecarbonthalogenbondsinorganichalideshavebeenoneofthemostchallengingproblemsanddesirablegoalsforchendsts.Oforganichalides,0rgancchlorideisthemodrmaforeundiDexPdrieerefD1thepeDfu3efulboinboLalindusny.However,because0ftheinertness0ftheirC-Clbonds,organicchloridesexhibitl0wre…     

Enantioselective Aldol Reaction of α-Ketoester and Cyclopentaone Catalyzed by L-Proline

A concise and enantioselective synthesis of (S)‐ethyl 2‐cyclopentyl‐2‐hydroxy‐2‐arylacetate, a key intermediate for the muscarinic receptor, is reported. The tertiary stereogenic center was constructed with good stereoselectivity through the L‐proline‐catalyzed direct asymmetric aldol reaction of ethyl arylglyoxylate and cyclopentanone. The carbonyl of the condensation product was reduced using a modified Clemmensen reaction which provided an easier workup and was more environmentally acceptable. The enantioselectivity of the aldol reactions was between 58.3%–93.2%, which means that the stereoselective is efficient in controlling configuration of reaction product.     

Asymmetric Hydroformylation of Olefins Catalyzed by a Chiral Diphosphite-Rhodium Complex

A C2-symmetrical aryl diphosphite derived from chiral binaphthol was prepared and its rhodium complex was used as catalysts in the asymmetric hydroformylation of olefins. High catalytic activity and good regioselectivity were observed. Up to 31.2% ee and 38.1% ee were achieved for the hydroformylation of 4-fluoro-styrene and vinyl acetate respectively. The influences of ligand-to-metal ratio, reaction temperature and the pressure of syn-gas on the enantioselectivity and regioselectivity were also studied.     

Homocoupling of Aryl Iodides Catalyzed by Cyclopalladated Complexes of Tertiary Arylamines

Homocoupling of aryl iodides catalyzed by cyclopalladated complexes of tertiary arylamines gives symmetric biaryls with good yields in DMA or ionic liquid [Bmim]BF4. This catalytic alternative of the Ullmann reaction has proved to be sensitive to both electronic and steric factors of substrates.     

Enantio- and Diastereoselective Synthesis of Chiral Tetrasubstituted α-Amino Allenoates Bearing a Vicinal All-Carbon Quaternary Stereocenter with Dual-Copper-Catalysis

The skeletons of chiral tetrasubstituted allenes bearing a vicinal all-carbon quaternary stereocenter are of importance but still challenging to synthesize. Herein, we report enantio- and diastereoselective γ-additions of 1-alkynyl ketimines with dual-copper-catalysis under mild conditions, affording chiral tetrasubstituted α-amino allenoates bearing a vicinal all-carbon quaternary stereocenter in high yields (up to 99 % yield) with excellent enantioselectivities (up to 99 % ee) and diastereoselectivities (up to >20 : 1 dr). Importantly, the stereodivergent synthesis of the products was realized by the asymmetric γ-addition reaction and the Grignard reagent promoted epimerization. Moreover, the dual-copper-catalyzed γ-addition reactions were smoothly applied to a gram-scale reaction and adopted to introduce chiral tetrasubstituted allenyl moieties into bioactive molecules. Mechanistic experiments and density functional theory (DFT) calculations demonstrated that the asymmetric γ-addition reactions were catalyzed by double chiral copper catalysts.     

Enantioselective Amination of β-Keto Esters Catalyzed by Chiral Calcium Phosphates

A catalytic enantioselective amination of β-keto esters using (S)-BINOL chiral calcium phosphate has been developed. The reaction produces chiral α-amino-β-keto ester derivatives in most cases with moderate to excellent enantioselectivities (up to 99 %) and good yields (up to 99 %). This mild synthetic method highlights a low catalyst loading and high catalytic efficiency. When the substrate backbone was changed to 1-tetralone-derived β-keto esters, unexpectedly high yields of selective redox products were obtained. The practicality of the reaction was realized by a scale-up without any significant loss in the enantioselectivity and yield. Chiral calcium phosphate was successfully recovered and reused for four runs, indicating its stability and high catalytic activity.     

Enantio- and diastereoselective Michael addition reactions of α-cyanoketones to nitroalkenes catalyzed by binaphthyl-derived organocatalyst

The catalytic enantioselective and diastereoselective Michael addition reactions promoted by chiral bifunctional organocatalysts are described. The treatment of α-cyanoketones with nitroalkenes under mild reaction conditions afforded the corresponding γ-niro α-cyanoketones with excellent diastereoselectivities (up to syn/anti >99/1) and excellent enantioselectivities (up to 99% ee).     

Asymmetric Reformatsky Reaction of Aldehydes Catalyzed by Novel β-Amino Alcohols and Zinc Complexes

A series of β-amino alcohols derived from (1R, 2S)-2-amino-1,2-diphenylethanol and substituted salicylaldehydes as novel chiral tridentate ligands has been applied to an asymmetric Reformatsky reaction of aldehydes with ethyl iodoacetate in the presence of ZnMe₂. This novel catalytic system produced the desired β-hydroxyl esters with moderate to good enantioselectivities (up to 81% ee) and yields for many aldehydes, including aromatic, heteroaromatic, conjugated, and aliphatic aldehydes.     

Aqueous-Phase Synthesis of α-Hydroxyphosphonates Catalyzed by β-Cyclodextrin

α-Hydroxyphosphonates were synthesized from aromatic/heteroaromatic aldehydes with triethyl phosphite in the presence of β-cyclodextrin in an aqueous medium. The β-cyclodextrin can be recovered and reused without loss of catalytic activity.     

Methyl Iodide Accelerated Asymmetric Epoxidation of Alkenes Catalyzed by Chiral Salen-Mn（Ⅲ） Complexes with Tertiary Amine Units

A series of chiral salen-Mn（Ⅲ） complexes featuring two tertiary amine units were synthesized and employed in the enantioselective epoxidation of unfunctionalized alkenes in the presence of pyridine N-oxide and 2,6-dimethylpyridine N-oxide as proximal ligands, respectively. Moderate to high enantioselectivity and acceptable yields were achieved when NaClO was used as terminal oxidant under CH2Cl2/H2O biphasic media. Methyl iodide was found to be an effective additive to accelerate the epoxidation, possibly owing to the formation of quaternary ammonium units on catalysts, which may facilitate the reaction in an oil/water biphasic medium. The subsequent stimulation experiment was carried out, and the resulting ESI-HRMS analysis revealed the formation of a novel （salen）manganese（m） intermediate featuring two quaternary ammonium units, and bearing a pyridine N-oxide and a molecule of water simultaneously axially-coordinated backbone.     

Oxidation of Alcohols Catalyzed by Ruthenium Complexes with Iodosylbenzene as Oxidant

Five ruthenium complexes such as Phen-Ru-Phen, Phen-Ru-Bipy, Phen-Ru-Quin, Quin-Ru-Quin and Bipy-Ru-Quin (where Phen=l, 10-phenanthroline, Quin=8-hydroxyquinoline, Bipy=2, 2‘-bipyridine) were synthesized and used as catalysts for the oxidation of benzylic and primary aliphatic alcohols with iodosylbenzene as oxidant. The oxidations were carried out at room temperature, affording the corresponding aldehydes and ketones with high selectivity.     

Enantioselective Pinacol Coupling of Aromatic Aldehydes Induced by Chiral Titanium Complexes

The reductive coupling of carbonyl compounds catalyzed by the transition metal is an important group of carbon-carbon bond forming reaction. The pinacol coupling reaction of aldehydes is one of the most efficient methods for synthesis of vicinal diols1. L…     

Investigation of Inclusion Complexes Between α-Cyclodextrin and Ferrocene by ESI-MSn and Cyclic Voltammetry

The inclusion complexes of α-cyclodextrin (α-CD) and FcCO2 (CH2)18(FcSH) and their self-as-sembled monolayers (SAMs) on gold surface were investigated by electrospray tandem ionization mass spectrometry (ESI-MS″) and cyclic voltammetry, respectively. The interfacial electrochemical response of the SAMs is related to the way in which the inclusion complexes formed.     

Investigation of Inclusion Complexes Between α-Cyclodextrin and Ferrocene by ESI-MSn and Cyclic Voltammetry

The inclusion complexes of α-cyclodextrin(α-CD) and FcCO2(CH2)18 (FcSH) and their self-assembled monolayers(SAMs) on gold surface were investigated by electrospray tandem ionization mass spectrometry(ESI-MSn) and cyclic voltammetry, respectively. The interfacial electrochemical response of the SAMs is related to the way in which the inclusion complexes formed.     

Enantio-, Regio-, and Chemoselective Reduction of Aromatic α-Diketones by Baker’s Yeast

Summary. The enantio- and regioselective reduction of several symmetric and nonsymmetrically para-substituted benzil derivatives (21–92%) was achieved by means of Saccharomyces cerevisiae (bakers yeast). After modification of the reaction conditions reduction of nonsymmetric -diketones led chemoselectively to chiral -hydroxy ketones with up to 82% ee.Received December 16, 2002; accepted (revised) January 9, 2003 Published online July 28, 2003     

Chiral Primary Amine Catalyzed α-Arylation of Simple Ketones via Asymmetric Retro-Claisen Cleavage

Highly enantioselective α-arylation of simple ketones has been achieved by chiral primary amine catalyzed asymmetric retro-Claisen cleavage of β-diketones. This mild organocatalytic strategy enables the construction of α-aryl tertiary carbon stereocenters in good yields and excellent enantioselectivities (up to 98 % ee) with the para-quinone monoimines as aryl sources. Furthermore, oxidative catalytic asymmetric α-arylation has also been realized with free p-aminophenols.