Nickel(0)-catalyzed disilylative and silastannylative cyclizations of 1,3-diene and tethered aldehyde

Nickel(0)-catalyzed bismetallative cyclization of 1,3-diene and a tethered aldehyde in the presence of PhF₂SiSiMe₃ or Me₃SiSnBu₃ gave the corresponding cyclized product having an allylsilyl or an allylstannyl unit in the side chain in good yields. The cyclized product obtained from the reaction in the presence of Me₃SiSnBu₃ had reactivity as an allylstannane derivative, and the coupling reaction with benzaldehyde proceeded in a diastereoselective manner. When the silastannylative cyclization was carried out in the presence of a chiral monodentate phosphine ligand, the cyclized product was produced as an optically active form with modest enantiomeric excess.     

New Bifunctional Bis(azairidacycle) with Axial Chirality via Double Cyclometalation of 2,2′-Bis(aminomethyl)-1,1′-binaphthyl

As a candidate for bifunctional asymmetric catalysts containing a half-sandwich C–N chelating Ir(III) framework (azairidacycle), a dinuclear Ir complex with an axially chiral linkage is newly designed. An expedient synthesis of chiral 2,2′-bis(aminomethyl)-1,1′-binaphthyl (1) from 1,1-bi-2-naphthol (BINOL) was accomplished by a three-step process involving nickel-catalyzed cyanation and subsequent reduction with Raney-Ni and KBH₄. The reaction of (S)-1 with an equimolar amount of [IrCl₂Cp*]₂ (Cp* = η⁵–C₅(CH₃)₅) in the presence of sodium acetate in acetonitrile at 80 °C gave a diastereomeric mixture of new dinuclear dichloridodiiridium complexes (5) through the double C–H bond cleavage, as confirmed by ¹H NMR spectroscopy. A loss of the central chirality on the Ir centers of 5 was demonstrated by treatment with KOC(CH₃)₃ to generate the corresponding 16e amidoiridium complex 6. The following hydrogen transfer from 2-propanol to 6 provided diastereomers of hydrido(amine)iridium retaining the bis(azairidacycle) architecture. The dinuclear chlorido(amine)iridium 5 can serve as a catalyst precursor for the asymmetric transfer hydrogenation of acetophenone with a substrate to a catalyst ratio of 200 in the presence of KOC(CH₃)₃ in 2-propanol, leading to (S)-1-phenylethanol with up to an enantiomeric excess (ee) of 67%.     

A novel type of catalysts for asymmetric oxidative coupling of 2-naphthol

Stereochemically inert, positively charged chiral octahedral complexes of Co^III and Cr^III were used as catalysts for asymmetric oxidative coupling of 2-naphthol. The reaction product 1,1´-bi-2-naphthol was produced with a yield of up to 74% and enantiomeric excess of up to 22%. The reduction and oxidation potentials of a series of Co^III and Cr^III cationic complexes were measured.     

High Resolution of Racemic Mandelic Acid through a Method of Bubble Fractionation

A method of bubble fractionation was developed for the resolution of racemic mandelic acid (MA), using 2‐hydroxypropyl‐β‐cyclodextrin (HP‐β‐CD) as chiral collector. The influences of concentration of HP‐β‐CD, reflux equilibriation time, gas flow rate, packing height of column and pH of buffer on resolution performance were investigated, respectively. According to the similar physical behavior of bubble fractionation and chemical reaction processes, the equivalent chemical reaction constant was introduced. The resolution process was preliminarily analyzed by means of kinetics. The results show that the enantiomeric excess of 60.7% can be obtained under the optimal conditions. The process could be regarded as a first order chemical reaction, where the equivalent speed constant was k_l=0.00376. This method is helpful for realizing high resolution and linear amplification of device.     

Systematic Study of the Asymmetric Methoxycarbonylation of Styrene Catalyzed by Palladium Systems Containing Chiral Ferrocenyl Diphosphine Ligands

We present the first systematic study of the Pd‐catalyzed asymmetric methoxycarbonylation of styrene in the presence of chiral ferrocenyl phosphine ligands. The reaction conditions were optimized, and a screening of different catalyst precursors was performed. A number of 1,1′‐bis(phosphino)ferrocenes of the Mandyphos, Josiphos, Walphos, and Taniaphos types were tested in combination with [PdCl₂(NCPh)₂], in the presence of TsOH as the acid source. These systems afforded high enantioselectivities, although the regioselectivity of the reaction was found to be in favor of the (undesired) linear ester. The catalytic system made with the Josiphos ligand 1 gave rise to an enantiomeric excess (ee) of 86%.     

Asymmetric 1,4-addition of organoboronic acids to α,β-unsaturated ketones and 1,2-addition to aldehydes catalyzed by a palladium complex with a ferrocene-based phosphine ligand

A combination of palladium with ferrocene-based phosphine ligand with a carbon–bromine bond was found to be a good catalyst for the 1,4-addition of arylboronic acids to α,β-unsaturated ketones and the 1,2-addition to aldehydes. Using Pd(dba)₂ and (S,R_p)-[1-(2-bromoferrocenyl)ethyl]diphenylphosphine (S,R_p)-1, 3-phenylcyclohexanone was obtained from the reaction of 2-cyclohexen-1-one with phenylboronic acid in the presence of K₂CO₃ in toluene at room temperature after 3 h in 92% yield with 76% ee. In the 1,2-addition of 4-methylphenylboronic acid to benzaldehyde, 96% of (4-methylphenyl)phenylmethanol was afforded after 24 h, while the enantiomeric excess was only 6%.     

A TFAA-H3PO4-mediated direct, metal-free and high-speed synthesis of aryl carboxylate esters from phenols

An operationally simple, mild and single-step method for the direct and metal-free synthesis of aryl carboxylate esters is described under a solvent free condition. The reaction of phenols including 2-naphthol (or 1-naphthol) with a variety of carboxylic acids in the presence of TFAA and 85% H₃PO₄ provided a range of aryl carboxylate esters in good yields within few minutes.     

Enantioselective oxidative-coupling of polycyclic phenols

Enantioselective oxidative-coupling of polycyclic phenols, such as 2-anthracenol, 9- or 3-phenanthrol, and 5-chrysenol was established by using vanadium(V/IV) catalysis under air or O₂ as a co-oxidant. In the vanadium catalyzed reaction, the corresponding coupling products were obtained in good to excellent yields with up to 93% enantiomeric excess.     

Synthesis of novel chiral Schiff-base ligands and their application in asymmetric nitro aldol (Henry) reaction

Chiral Schiff-bases prepared from chiral amino alcohols catalyze the enantioselective Henry (nitro aldol) reaction between nitromethane and p-nitrobenzaldehyde in the presence of Cu(OTf)₂ and Zn(OTf)₂. Zn(OTf)₂ promoted the reaction yield, while Cu(OTf)₂ promoted the enantiomeric excess. The highest enantioselectivities were observed with ligand 3 (44% ee) and ligand 5 (47% ee).     

Synthesis of a novel cyclodextrin dimer linked by a macrocyclic polyamine

The first example of cyclodextrin dimer appending a macrocyclic polyamine spacer on the primary faces was synthesized via two approaches: 1,a direct reaction of l,7-bis(2'-aminoethyl)-4,10-dimethyl-l,4,7,10-tetraazacyclododecane (1) with an excess of 6-deoxy-6-O-tosyl-β-cyclodextrin; 2,a condensation of 1 with two equivalents of 6-deoxy-6-formyl-β-cyclodextrin,which was followed by a reduction with NaBH4.     

Synthese D'α-hydroxy acides optiquement actifs

The reaction of chiral MAIR₃OR^* (M = Li, Na, K ; R = Me, Et ; OR^* from R^*OH = (?)N-methylephedrine) with C₆H₅COCO₂ (?)-menthyl provide a good synthesis of α-alkyl mandelic acids with enantiomeric excess (e.e.) up to 53%. Asymmetric induction due to both the chiral centers of the (?)-menthyl group and the OR^* group may be invoked to account for the higher stereoselectivity observed in the reaction.     

Enantiomeric separation of some common controlled stimulants by capillary electrophoresis with contactless conductivity detection

CE methods with capacitively coupled contactless conductivity detection (C⁴D) were developed for the enantiomeric separation of the following stimulants: amphetamine (AP), methamphetamine (MA), ephedrine (EP), pseudoephedrine (PE), norephedrine (NE) and norpseudoephedrine (NPE). Acetic acid (pH 2.5 and 2.8) was found to be the optimal background electrolyte for the CE‐C⁴D system. The chiral selectors, carboxymethyl‐β‐cyclodextrin (CMBCD), heptakis(2,6‐di‐O‐methyl)‐β‐cyclodextrin (DMBCD) and chiral crown ether (+)‐(18‐crown‐6)‐2,3,11,12‐tetracarboxylic acid (18C6H₄), were investigated for their enantioseparation properties in the BGE. The use of either a single or a combination of two chiral selectors was chosen to obtain optimal condition of enantiomeric selectivity. Enantiomeric separation of AP and MA was achieved using the single chiral selector CMBCD and (hydroxypropyl)methyl cellulose (HPMC) as the modifier. A combination of the two chiral selectors, CMBCD and DMBCD and HPMC as the modifier, was required for enantiomeric separation of EP and PE. In addition, a combination of DMBCD and 18C6H₄ was successfully applied for the enantiomeric separation of NE and NPE. The detection limits of the enantiomers were found to be in the range of 2.3–5.7 μmol/L. Good precisions of migration time and peak area were obtained. The developed CE‐C⁴D method was successfully applied to urine samples of athletes for the identification of enantiomers of the detected stimulants.     

Simultaneous Determination of Concentration and Enantiomeric Composition of Amino Acids in Aqueous Solution by Using a Tetrabromobinaphthyl Dialdehyde Probe

3,3′-Diformyl-1,1′-bi-2-naphthol or its methoxymethyl-protected derivative is found to undergo a highly selective reaction with excess bromine in CH₂Cl₂ at reflux to give the novel 5,5′,6,6′-tetrabrominated product (S)- or (R)- 2 . The observed electrophilic substitution at the 5,5′-positons of an optically active binaphthyl compound is unprecedented. Unlike unbrominated 3,3′-diformyl-1,1′-bi-2-naphthol, which is not suitable for fluorescent recognition in water, compound (S)- 2 , in combination with Zn²⁺, exhibits a highly enantioselective fluorescent response toward amino acids in aqueous solution (HEPES buffer, pH 7.4). It is further found that the condensation product of (R)- 2 with tryptophan, (R)- 3 , shows dual-responsive emissions toward amino acids; the short wavelength (λ₁=350 nm) emission is sensitive to the concentration of the substrate regardless of the chiral configuration and the long wavelength (λ₂>500 nm) emission is highly enantioselective. Thus, the use of (R)- 3 allows the simultaneous determination of the concentration and enantiomeric composition of an amino acid sample from one fluorescence measurement.     

The effect of benzyl amine on the efficiency of the base-catalyzed transamination of α-keto esters

This paper describes the effect of benzyl amine on the base-catalyzed transamination of α-keto esters. Among various benzyl amines examined, o-HOC₆H₄CH₂NH₂ was found to be highly effective for the reaction, affording a wide variety of α-amino esters in good yields. The o-OH group of the benzyl amine facilitates the transamination process likely via H-bond. Moderate enantiomeric excess was obtained for α-amino ester when a quinine derived catalyst was used.     

Straightforward access to chiral diol bidentate ligands: their efficient enantioselective induction in the addition of diethylzinc to aromatic aldehydes

Enantiopure C₂‐symmetric diol bidentate ligands have been synthesized in a straightforward manner through a three‐step reaction with good yields. The synthesized C₂‐symmetric diol bidentate ligands were used in the addition of diethylzinc to various aromatic aldehydes, a general catalytic benchmark reaction, in order to assess their enantioselective induction properties. The enantioselective addition of diethylzinc to 1‐naphthaldehyde and 3‐chlorobenzaldehyde was achieved with an enantiomeric excess (ee) of up to 98%. All synthesized ligands were also evaluated in the addition of diethyzinc to aromatic aldehydes including an extra metal such as Ti(IV) (up to 99% ee). Copyright © 2014 John Wiley & Sons, Ltd.     

Synthesis and polymerization of racemic and optically active β-substituted β-propiolactones. II: β-monosubstituted and β-disubstituted monomers and polymers with different optical purities

β-(trichloromethyl)-β-propiolactone (CCl₃-PL), β-(trifluoromethyl,methyl)-β-propiolactone (CF₃, Me-PL) and β-(trifluoromethyl,ethyl)-β-propiolactone (CF₃,Et-PL) have been obtained by the reaction of ketene with chloral, 1,1,1-trifluoroacetone and 1,1,1-trifluorobutanone, respectively. Chiral catalysis lead to optically active monomers. The enantiomeric excess of the lactones has been measured by ¹H-NMR spectroscopy, in the presence of 2,2,2-trifluoro-1-(9-anthryl)ethanol or an europium chiral shift reagent. Polymerizations have been carried out in bulk or in toluene, at 60°C or 80°C, using mainly organometallic initiators. The Polymers become insoluble and crystalline at enantiomeric excesses over 80% for CCl₃-PL and 70% for CF₃,Me-PL. Melting temperatures were recorded from 238 to 268°C for poly(CCl₃-PL) and from 78 to 100°C for poly(CF₃,Me-PL), depending upon the molecular weight and the enantiomeric excess. The ¹³C-NMR specroscopy of poly(CCL₃-PL) indicates that the polymerization of the corresponding lactone leads to polymers of increasing degrees of isotacticity with the enantiomeric excess of the monomer.     

A catalytic asymmetric approach to C1-chiral 3-methylene-indan-1-ols

A sequential (R)-BINAP·Ag^IF (2,2′-bis(diphenylphosphino)-1,1′-binaphthyl) (6–10 mol %), and (Ph₃P)₂Pd^IICl₂ (bis(triphenylphosphine)palladium(II) dichloride) (2 mol %) catalyzed asymmetric Sakurai–Hosomi–Yamamoto allylation/Mizoroki–Heck reaction that affords C₁-chiral 3-methylene-indan-1-ols with enantiomeric excess (ee) up to 80% is reported. Notably, this protocol allows for the use of various o-substituted benzaldehydes and allyltrimethoxysilane. It was also discovered that the presence of electron-rich groups had no effect on the enantioselectivity of the reaction, whereas electron-withdrawing groups lead to erosion in product ee.     

Über Reaktionen von Nitrosophenolen, 4. Mitt.: Reaktion von Nitrosonaphtholen mit Naphtholen

Zusammenfassung Die Reaktion von 1-Nitroso-2-naphthol mit 1-und 2-Naphthol sowie die Reaktion von 2-Nitroso-1-naphthol mit 2-Naphthol in Äthanol und in Äther bei Anwesenheit von HNO₃ gibt 5H-Dibenzo[a,j]phenoxazon-(5) (I), 5H-Dibenzo[a,j]phenoxazon-(5)-14-oxid (II), 5H-Dibenzo[a,h]phenoxazon-(5) (III) sowie 5H-Dibenzo[a,h]phenoxazon-(5)-14-oxid (IV). Es wurde ein Reaktionsmechanismus vorgeschlagen und die Konstitution der hergestellten Verbindungen spektrophotometrisch und potentiometrisch bestimmt.

---

The reaction of 1-nitroso-2-naphthol with 2-and 2-naphthol and the reaction of 2-nitroso-1-naphthol with 2-naphthol in ethanol or ether in the presence of nitric acid have been studied. The main reaction products isolated were the dibenzophenoxazones I–IV. The reaction mechanism for their formation is proposed.

---

---

Mit 4 Abbildungen     

Synthesis and Polymerization of Carbamate-Linked Cyclodextrin Methacrylate Monomers

Abstract

A one-step synthesis for cyclodextrin methacrylate monomers was examined starting from α-, β- and γ-cyclodextrin. The reaction of 2-isocyanatoethyl methacrylate as well as allylisocyanate with the corresponding cyclodextrin gave the monofunctionalized carbamate-linked cyclodextrin methacrylates 2, 6 and 9 and allylcarbamates 11 and 14 in moderate yields. By NMR spectroscopic means, it could be proven that in all cases only the primary 6-hydroxyl groups of the cyclodextrins reacted with the isocyanate group. For the synthesis of a β-cyclodextrin monoallyl compound, a substitution reaction of purchasable 6-O-monotoluenesulfonyl-β-cyclodextrin with allylamine gave 6-N-allylamino-6-deoxy-β-cyclodextrin 18 in high yield. The reaction of 2-isocyanatoethyl methacrylate with α-cyclodextrin to the 6-O-carbamoyl-2-methylpropenoylethyl-α-cyclodextrin (2) was optimized so that the monomer 2 could be prepared on a larger scale without chromatographic separation. The aqueous radical homopolymerization of 2 with the peroxodisulfate/bisulfite redox initiator gave the water soluble cyclodextrin polymer 19 in good yield. Its molecular weight was determined by gel permeation chromatography to be M_n = 101,800 corresponding to an average degree of polymerization P_n = 90.     

N-tert-Butyldimethylsilyl Imines as Intermediates for the Synthesis of Amines and Ketones

Grignard reagents add to benzonitrile at low temperature catalyzed by CuBr and TBSCl affording N-TBS ketimines, which were investigated as intermediaries for the synthesis of primary amines and ketones. N-silylimines were easily obtained by an organolithium addition to benzonitrile followed by a reaction with TBSCl in CH₂Cl₂. In situ reduction of these imines by BH₃ and 1,3,2-oxazaborolidines 1 or 2 as chiral templates afforded the corresponding amines with modest to good enantiomeric excess.