Enantioselective phenylacetylene addition to aldehydes and ketones catalyzed by recyclable polymeric Zn(salen) complex

New polymeric Zn(salen) complex was employed in the enantioselective phenylacetylene addition to aldehydes and ketones to produce corresponding chiral secondary propargylic alcohols with yields (up to 96%) and enantioselectivity (up to 72%) and tertiary propargylic alcohols with yields (up to 79%) and enantioselectivity (up to 68%) at room temperature, with added advantage of four times reuse with retention of enantioselectivity.     

Asymmetric addition of phenylacetylene to aromatic ketones catalyzed by zinc or titanium complexes with chiral hydroxysulfonamide

Various new chiral hydroxysulfonamide ligands (3a-3n, 4a-4d) were prepared. Compounds 3a, 3g, 3i, 3k-3n, 4a-4d could accelerate the reaction and reduce reaction time, and 3a, 3g, 3i, 3k-3n catalyzed the reaction without titanium. The results obtained were promising in terms of yields and enantiomeric excesses (3k up to 85% ee, 4a up to 83% ee).     

Readily available sulfamide-amine alcohols for enantioselective phenylacetylene addition to aldehydes in the absence of Ti(O(i)Pr)4

Ephedrine-derived sulfamide-amine alcohol 3 was found to be an effective catalyst for the asymmetric phenylacetylene addition to aldehydes at room temperature without using Ti(O(i)Pr)4 and Zn(OTf)2. It afforded the propargylic alcohols in high yields (up to 99%) and good enantioselectivities (up to 84% ee), which were much higher than that based on N-methylephedrine under the same reaction conditions. Its weakly coordinative sulfonamide moiety of the ligand plays an important role for further acceleration and stereocontrol in the alkynylation.     

Enantioselective conjugate addition of ketones to nitroalkenes catalyzed by pyrrolidine-sulfamides

A series of chiral pyrrolidine-sulfamides were prepared and examined as the catalysts for conjugate addition of ketones to nitroalkenes. Benzoic acid was identified as the most efficient additives for the transformation. Excellent enantioselectivities, diastereoselectivities, and yields were achieved for the reaction of cyclohexanone with β-aryl nitroethylenes under solvent free conditions. β-Isopropyl nitroethylene is also applicable and the product could be obtained with excellent enantioselectivity after extended reaction time. A comparison of the catalytic behaviors of pyrrolidine-sulfamide organocatalysts with different side chains demonstrates that the enantioselectivity is mainly controlled by the chiral pyrrolidine unit and the additional chiral center at the side chain exerts neglectable effects. The H-bonding interaction between the sulfamide and the nitro group is proposed to be crucial for the activation of the nitroalkene and the constitution of well-organized transition state.     

Enantioselective vinylation of aldehydes with the vinyl Grignard reagent catalyzed by magnesium complex of chiral BINOLs

Enantioselective vinylation of aldehydes via direct catalytic asymmetric Grignard reaction of aldehdyes and the vinyl Grinard reagent is a long‐standing challenge. This work demonstrated that the magnesium (S)‐3,3′‐dimethyl BINOLate enantioselectively catalyze the direct vinylation of aldehydes with the deactivated vinylmagnesium bromide by bis(2‐[N,N′‐dimethylamino]ethyl) ether (BDMAEE) in the addition of n‐butylmagnesium chloride. The highest ee of 63% was achieved up to date.     

A Simple Chiral Cu(II) Complex as an Effective Phase‐Transfer Catalyst for the Enantioselective Alkylation of Dissymmetric Glycinate Ketimines

Catalytic asymmetric benzylation of a dissymmetric tert‐butylglycinate ketimine, incorporating 1‐naphthyl and phenyl groups as the Schiff base substituents, under phase‐transfer conditions was investigated. It was interesting to note that the sense of asymmetric induction of the alkylation of Z‐imine stereoisomer is opposite to that of the corresponding E stereoisomer with a similar degree of enantioselectivity. More interestingly, the chiral Cu(II) complex of the Schiff base derived from (R)‐2‐phenylglycinol and 2‐hydroxy‐1‐naphthaldehyde was found to catalyze the same reaction under solid‐liquid conditions with comparable enantioselectivity (up to 60% ee) with respect to known cinchona alkaloid catalysts. The solvent/base‐system parameter was shown to control the optimal catalytic activity. Chirality 27:944–950, 2015. © 2015 Wiley Periodicals, Inc.     

Enantioselective conjugate addition of diethylzinc to cyclic enones catalyzed by copper complexes of methylene-bridged P-chirogenic diphosphines

The copper-catalyzed enantioselective conjugate addition of diethylzinc to 2-cyclohexen-1-one was investigated using (R,R)-bis-(t-butylmethylphosphino)methane (1c) as a chiral ligand. The reaction was carried out at 0 degrees C in THF-toluene as the solvent system and in the presence of 1.2 mol% of CuOTf afforded (S)-3-ethylcyclohexan-1-one with 85% ee.     

Enantioselective addition of diethylzinc to aldehydes catalyzed by titanium(IV) complexes of N-sulfonylated beta-amino alcohols with four stereogenic centers

An N-sulfonylated beta-amino alcohol (R,S,S,R)-9 with four stereogenic centers is prepared. The titanium complex of 9 is an effective catalyst to induce excellent enantioselectivities for diethylzinc addition to aromatic aldehydes with ee values up to 99%. The feature of doubling the quantity of Ti(O-i-Pr)4 required relative to the catalytic system of the Ti complex of bidentate N-sulfonylated beta-amino alcohols suggests that the two N-sulfonylated beta-amino alcohol moieties in 9 behave as two independent bidentate ligands in the catalytic system. The results obtained using ligand 15 having one N-sulfonylated beta-amino alcohol blocked support the argument of two independent active bidentate moieties in 9.     

Enantioselective addition of diethylzinc to aldehydes catalyzed by optically active C2-symmetrical bis-beta-amino alcohols

The syntheses of new optically active C(2)-symmetrical bis-beta-amino alcohols 1-6 from (S)-2-(1-hydroxy-1,1-diphenylmethyl)-pyrrolidine are described. Especially attention is focused on bridges, which link the two beta-amino alcohol units. These new chiral ligands have been successfully applied in the catalytic enantioselective addition of diethylzinc to aldehydes to give sec-alcohols in good yields with up to 95% enantiomeric excess.     

Enantioselective reduction of C=N double bond by chromium(II) complexes of natural amino acids

Asymmetric reduction of oximes was performed by chromium(II) complexes of natural amino acids in aqueous phase or in H(2)O/DMF (1:1) solvent. Medium-to-quantitative chemoselectivity (54% to >95%) and low-to-medium enantioselectivity (5-50% ee) were found.     

Synthesis and application of chiral beta-amino disulfides as ligands for the enantioselective addition of diethylzinc to aldehydes

A new class of chiral beta-amino disulfides was synthesized from readily available and inexpensive starting materials by a straightforward method and their abilities as ligands were examined in the enantioselective addition of diethylzinc to aldehydes. Enantiomeric excesses of up to 99% have been obtained using 0.5 mol % of the chiral catalysts.     

Enantioselective copper-aminopyridine-catalyzed aza-Henry reaction with chelating N-(2-pyridyl)sulfonyl imines

This article describes a copper-catalyzed aza-Henry reaction. Copper complexes of camphor-derived aminopyridines catalyze the addition of nitromethane to N-(2-pyridyl)sulfonyl aldimines to give the corresponding β-nitrosulfonamides with good yields and variable enantiomeric excesses (up to 83%). An example of transformation of these compounds into N-(2-pyridyl)sulfonyl-α-amino acids and deprotection of the sulfonamide with Mg-MeOH is provided.     

Enantioselective addition of phenylacetylene to aldehydes catalyzed by polymer‐supported titanium(IV) complexes of β‐hydroxy amides

A series of polymer‐supported chiral β‐hydroxy amides and C₂‐symmetric β‐hydroxy amides have been synthesized and successfully used for the enantioselective addition of phenylacetylene to aldehydes. High yields (up to 93%) and enantioselectivities (up to 92% ee) were achieved by using polymer‐supported chiral β‐hydroxy amide 4b . The resin 4b is reused four times, giving the product with enantioselectivity 80% ee. Fortunately, it is found that this heterogonous system is suitable not only for aromatic aldehydes but also aliphatic aldehyde. Chirality, 2010. © 2009 Wiley‐Liss, Inc.     

Palladium(II) complexes of the chiral pinBPI ligand

The chiral bis(pyridylimino)isoindoline derivative 5 (pinBPI) was prepared from the chiral pool reagent α-pinene 1 in three steps and an overall yield of 12%. Upon treatment with palladium(II) acetate and palladium(II) chloride, pinBPI 5 forms the nonracemic chiral complexes [(pinBPI)Pd(OAc)] 6 and [(pinBPI)PdCl] 7, respectively, as the only isolated species in good yield. The synthesis of a related thiazole-based ligand failed for the incompatibility of the four-membered carbocycle of the pinene subunit with the conditions of the thiazole-forming reaction. Both pinBPI chelates crystallize in chiral space groups but with different molecular conformations and intermolecular interactions. A triclinic system with space group P1 is found for the acetato derivative 6 which organizes pseudosymmetrically as a chloroform solvate with one helical and one (almost) planar molecule in the asymmetric unit. The chloro derivate 7 on the other hand crystallizes in the monoclinic space group P2₁ with Z = 8 and four independent molecules in the unit cell. Here, all molecules are in a pseudoplanar configuration with convex ligand conformations, but differ significantly in bond lengths and angles. The structures unravel two different possible scenarios for intermolecular association of such chiral BAI ligands.     

An unsaturated half-sandwich ruthenium(II) complex containing a dithioimidodiphosphinate ligand

Treatment of [Cp*RuCl₂]_x (Cp* = η⁵-C₅Me₅) with K[N(Ph₂PS)₂] afforded [Cp*Ru{N(Ph₂PS)₂}Cl] (1). Reduction of 1 with Li[BEt₃H] gave the 16-electron half-sandwich Ru(II) complex [Cp*Ru{N(Ph₂PS)₂}] (2). Complexes 1 and 2 have been characterized by X-ray crystallography. The Ru-Cp*(centroid) and average Ru-S distances in 1 are 1.827 and 2.3833(5) Å, respectively. The corresponding bond distances in 2 are 1.739 and 2.379(1) Å. Treatment of 2 with 2-electron ligands L afforded the adducts [Cp*Ru{N(Ph₂PS)₂}L] (L = CO (3), 2,6-Me₂C₆H₄NC (4), MeCO₂CCCO₂Me (5)). Oxidation of 2 with tetramethylthiuram disulfide gave the Ru(IV) complex [Cp*Ru{S₂CNMe₂}₂][N(Ph₂PS)₂] (6). The Ru-Cp*(centroid) and average Ru-S distances in 6 are 1.897 and 2.387(1) Å, respectively.     

Density functional computations of enantioselective alkynylation of aldehyde catalyzed by chiral zinc(II)-complexes

The enantioselective alkynylation of aldehyde catalyzed by chiral zinc(II)-complexes was studied by means of the density functional theory (DFT). All the structures were optimized completely at the B3LYP/6-31G(d,p) level. To obtain more exact energies, single-point energy calculations at B3LYP/6-31+G(d,p) level were carried out on the B3LYP/6-31G(d,p) geometries. As shown, this enantioselective alkynylation was endothermic. The chirality-determining step for the alkynylation was the formation of the catalyst–ethanol complexes and the transition states for this step involved a six-membered ring. The dominant products predicted theoretically were of (R)-chirality, in good agreement with experiment.      

Syntheses, structures, and properties of tricarbonyl rhenium(I) heteronuclear complexes with the multidentate bridging ligand containing bis(2-pyridine) and carboxylic acid

By deprotonation reaction of the rhenium(I) tricarbonyl complex, ClRe(CO)₃(H₂bpydt) (2, H₂dpydt = 2-(di(2-pyridyl)methylene)-1,3-dithiole-4,5-dicarboxylic acid, our previous work in J. Organomet. Chem. 694 (2009) 763), complex 3, [Bu₄N][ClRe(CO)₃(Hbpydt)], is synthesized and characterized. Using 3 as the starting material, two trinuclear heterometallic complexes M(MeOH)₄[ClRe(CO)₃(Hbpydt)]₂·2MeOH (M = Cu, 4; M = Mn, 5) are obtained. The crystal structures of 2-5 have been determined by X-ray crystallography. Complexes 4 and 5 are isostructural. Their absorption and emission properties are studied. The magnetic properties of complexes 4 and 5 have also been investigated.     

Interaction of polypyridyl ruthenium (II) complex containing asymmetric ligand with DNA

A novel asymmetric bidentate ruthenium (II) complex, [Ru(bpy)(2)(PYNI)](2+) (bpy=2,2'-bipyridine, PYNI=2-(2'-pyridyl)naphthoimidazole), has been synthesized and characterized by elemental analysis, ES-MS (electrospray mass spectra) and (1)H NMR. The electrochemical behaviors of this complex were studied by cyclic voltammetry. DNA interaction studies suggest that [Ru(bpy)(2)(PYNI)](2+) binds to calf thymus DNA (CT-DNA) in an intercalative mode. Interestingly, this new Ru(II) complex has also been found to promote cleavage of plasmid pBR 322 DNA from the supercoiled form I to the open circular form II upon irradiation.     

Structure and magnetic properties of a tetranuclear Cu(II) complex containing the 2-(pyridine-2-yliminomethyl)-phenol ligand

A tetranuclear Cu(II) complex [Cu₄L₄(H₂O)₄](ClO₄)₄ has been synthesized using the terdentate Schiff base 2-(pyridine-2-yliminomethyl)-phenol (HL) (the condensation product of salicylaldehyde and 2-aminopyridine) and copper perchlorate. Chemical characterizations such as IR and UV/Vis of the complex have been carried out. A single-crystal diffraction study shows that the complex contains a nearly planar tetranuclear core containing four copper atoms, which occupy four equivalent five-coordinate sites with a square pyramidal environment. Magnetic measurements have been carried out over the temperature range 2-300 K and with 100 Oe field strengths. Analysis of magnetic susceptibility data indicates a strong antiferromagnetic (J₁ = −638 cm⁻¹) exchange interaction between diphenoxo-bridged Cu(II) centers and a moderate antiferromagnetic (J₂ = −34 cm⁻¹) interaction between N-C-N bridged Cu(II) centers. Magnetic exchange interactions (J’s) are also discussed on the basis of a computational study using DFT methodology. The spin density distribution (singlet ground state) is calculated to visualize the effect of delocalization of spin density through bridging groups.     

Synthesis and characterization of Cu(II) and Ni(II) complexes of a tripodal ligand containing imidazoles

Two complexes of the formula [MH₃L](ClO₄)₂ [M = Cu(II) (1), Ni(II) (2)] have been prepared by the reaction of M(ClO₄)₂ · 6H₂O with the ligand (H₃L) formed by the Schiff base condensation of tris(2-aminoethyl)amine (tren) with three molar equivalents of 4-methyl-5-imidazolecarboxaldehyde and structurally and magnetically characterized. The structures of 1 and 2 are isomorphous with each other and with the iron(II) complex of H₃L which has been reported previously. The ligand, while potentially heptadentate, forms six coordinate complexes with both metal centers forming three M-N_imine and three M-N_imidazole bonds. The tren central N atom is at a nonbonded distance from M of 3.261 Å for 1 and 3.329 Å for 2. The neutral complex CuHL 3 was prepared by reaction of H₃L with Cu(OCH₃)₂ and the ionic complex Na[NiL] 4 was prepared by deprotonation of 2 with aqueous sodium hydroxide. Magnetic measurements of 1-3 are consistent with the spin-only values expected for S = 1/2 (d⁹, Cu(II)) and S = 1 (d⁸, Ni (II)) systems.