Y(OTf)3 as a highly efficient catalyst in Ferrier Rearrangement for the synthesis of O- and S-2,3-unsaturated glycopyranosides

By using Y(OTf)₃ as the catalyst, a series of 2,3-unsaturated-glucosides have been synthesized from 3,4,6-tri-O-acetyl-d-glucal, 3,4-di-O-acetyl-l-rhamnal, and 3,4,6-tri-O-benzyl-d-glucal under mild reaction conditions in good yields with high anomeric selectivities. It was found that, in this reaction, 3,4,6-tri-O-benzyl-d-glucal behaved differently from the other two glucals when it was reacted with phenol, O-benzyl glucoside instead of O-phenyl glucoside formed as the sole product. An explanation is given for this phenomenon.     

RuCl3·3H2O as catalyst for Ferrier rearrangement: an efficient procedure for the preparation of pseudoglycosides

By using RuCl₃·3H₂O as catalyst, an improved method for the synthesis of 2,3-unsaturated-glycosides has been established. A series of 2, 3-unsaturated-glucosides were obtained from 2,4,6-tri-O-acetyl-d-glucal or 3,4-di-O-acetyl-6-deoxy-l-glucal in good yield and high anomeric selectivity.     

Ferrier Reaction: The first synthesis of 2,3-unsaturated seleno-glycosides by using alkyl(aryl) hydroselenides as the nucleophile and Hf(OTf)4 as the catalyst

By using Hf(OTf)₄ as the catalyst, a series of 2,3-unsaturated-Se-glucosides have been synthesized for the first time from tri-O-acetyl-d-glucal, 2,4,6-tri-O-benzyl-d-glucal, 3,4-di-O-acetyl-l-rhamnal and ((2R,3S)-3-acetoxy-2,3-dihydrofuran-2-yl) methyl acetate with PhSeH or alkyl(aryl) hydroselenides as the nucleophile in good yield and high anomeric selectivity.     

Synthetic studies of erythromycin derivatives: 6-O-methylation of (9S)-12,21-anhydro-9-dihydroerythromycin A derivatives

Synthetic studies on methylation of erythromycin derivatives were conducted. Methylation of 6 resulted in the formation of the C-3′ quaternary ammonium salts with a rate faster than 6-O-methylation. In dipolar aprotic solvent and under strong base conditions, 6-O-methylation, C-3′ quaternary ammonium salts formation and 2-C-methylation proceeded simultaneously to yield a mixture of three different products 7, 8 and 9. The quaternary ammonium salts were converted back to the corresponding tertiary amines 2, 10 and starting material 6 by employing sodium 4-pyridinethiolate as a N-demethylation reagent. The 6-O-methylation was eventually achieved in a good yield when a carbobenzyloxy (Cbz) group was utilized to protect the C-3′-dimethylamino group of 4. In this report, we will discuss the details of different reaction courses in the methylation of (9S)-12, 21-anhydro-9-dihydroerythromycin A derivatives.     

Application of cyclic-1,3-diketones in domino and multicomponent reactions: facile route to highly functionalized chromeno[2,3-d]pyrimidinones and diazabenzo[b]fluorenones under solvent-free conditions

A facile and efficient protocol for the synthesis of chromeno[2,3-d]pyrimidinones and diazabenzo[b]fluorenones has been developed by one-pot three-component cyclocondensation of aldehydes, cyclic-1,3-diketones and 1,3-dimethylbarbituric acid in the presence of InCl₃ or P₂O₅ under solvent-free conditions.     

Convenient synthesis of N-isobutyryl-2′-O-methyl guanosine by efficient alkylation of O-trimethylsilylethyl-3′,5′-di-tert-butylsilanediyl guanosine

We present a novel route for the synthesis of N²-isobutyryl-2′-O-methyl guanosine, introducing 3′,5′-di-tert-butylsilyl and O⁶-trimethylsilylethyl groups as efficient protections during the 2′-O-methylation step with NaH/CH₃I. These protections were then removed simultaneously in a single step with TBAF. The eight-step synthesis is easy to perform, employing convenient commercially available reagents; crude mixtures are of satisfying purity, so only three chromatography purifications were required. Title compound was obtained in 25% overall yield from guanosine.     

Armed-disarmed effect of remote protecting groups on the glycosylation reaction of 2,3-dideoxyglycosyl donors

The armed-disarmed effect of remote protecting groups at the C-4 and/or C-6 position(s) on the glycosylation reactions of 2,3-dideoxyglycosyl donors was investigated. It was found that under various glycosylation conditions, 4- or 6-O-Bn 2,3-dideoxyglycosyl donors were much more reactive than the corresponding 4,6-di-O-Bz 2,3-dideoxyglycosyl donors. Based on these results, an effective and chemoselective glycosylation reaction using 4,6-di-O-Bn glycosyl acetate and 4-OH-6-O-Bz glycosyl acetate was realized, producing a 2,3-dideoxydisaccharide in good yield with high α-stereoselectivity.     

Nano-ferrous ferric oxide (nano-Fe3O4): Powerful,reusable, and stable catalyst for N-Boc protection of amines

Nano-ferrous ferric oxide (nano-Fe₃O₄) efficiently catalyzed N-boc protection of amines in high yields and acceptable reaction times. Nano-Fe₃O₄ was applied as an efficient, green, heterogeneous and reusable magnetite catalyst. Clean reaction, simple purification, short reaction time and high yield were some other advantages of this compound.     

Chemoenzymatic synthesis of a focused library of enantiopure structured 1-O-alkyl-2,3-diacyl-sn-glycerol type ether lipids

A highly efficient two-step chemoenzymatic synthesis of enantiopure structured ether lipids of the 1-O-alkyl-2,3-diacyl-sn-glycerol type has been developed. Chimyl, batyl and selachyl alcohols possessing pure saturated fatty acid (SFA) attached to the sn-3 position and pure EPA and DHA attached to the sn-2 position were obtained under full regiocontrol. This was offered by mild conditions and a highly efficient lipase that operated at room temperature. High-resolution ¹H NMR spectroscopy was used to monitor the progress of the reactions and to evaluate the full regiocontrol of the reactions involved by keeping track of all prospective adducts involved in these reactions. This was extended to preparation of a focused library of eight monoacyl intermediate adducts for all even-numbered SFA ranging from C₂-C₁₆ and the corresponding EPA and DHA structured diacyl glycerol ethers (DAGE) products for chimyl, batyl and selachyl alcohols, the total of 72 compounds.     

Scope of AuCl3 in the activation of per-O-acetylglycals

Gold(III)chloride in catalytic amounts activates 3,4,6-tri-O-acetyl-d-glucal, 3,4,6-tri-O-acetyl-d-galactal, and 3,4-di-O-acetyl-l-rhamnal efficiently. The activated species can be employed in the Ferrier reaction with different nucleophiles at ambient conditions. Attempts have been made to make β-anomer of the Ferrier product from anomeric-O-propargylated Ferrier product.     

Regioselective cleavage of the bis-benzylidene acetal of d-mannitol under oxidative and reductive conditions: a new approach to C2-symmetric chiral ligands

A highly regioselective oxidative cleavage of 1,3:4,6-di-O-benzylidene-d-mannitol was carried out using NBS and the resultant product was readily converted to the C₂-symmetric chiral ligand, (R,R)-3,4-dihydroxy-1,5-hexadiene. On the other hand, reductive cleavage of 1,3:4,6-di-O-benzylidene-d-mannitol was achieved in a highly regioselective manner using BF₃·OEt₂ and Et₃SiH to give a highly functionalized benzyl ether, which was converted to a synthetically useful C₂-symmetric bis-amino alcohol derivative.     

Development and validation of a nonaqueous capillary electrophoretic method for the enantiomeric purity determination of a synthetic intermediate of new 3,4-dihydro-2,2-dimethyl-2H-1-benzopyrans using a single-isomer anionic cyclodextrin derivative and an ionic liquid

The enantiomeric purity determination of a synthetic intermediate of new 3,4-dihydro-2,2-dimethyl-2H-1-benzopyrans, i.e. 4-amino-2,2-dimethyl-6-ethoxycarbonylamino-3,4-dihydro-2H-1-benzopyran, was successfully carried out using an anionic cyclodextrin (CD) derivative combined with a chiral ionic liquid (IL). In order to obtain high resolution and efficiency values, the addition of a chiral IL, i.e. ethylcholine bis(trifluoromethylsulfonyl)imide (EtChol NTf₂), to the background electrolyte containing heptakis(2,3-di-O-methyl-6-O-sulfo)-β-CD (HDMS-β-CD) was found to be essential. A simultaneous increase in separation selectivity and enantioresolution seems to indicate a synergistic effect of HDMS-β-CD and EtChol NTf₂. The best enantioseparation of the key intermediate was achieved using a methanolic solution of 0.75 M formic acid, 10 mM ammonium formate, 1.5 mM HDMS-β-CD and 5 mM EtChol NTf₂. Levamisole was selected as internal standard. The optimized conditions allowed the determination of 0.1% of each enantiomer in the presence of its stereoisomer using the method of standard additions. The NACE method was then fully validated with respect to selectivity, response function, trueness, precision, accuracy, linearity and limits of detection and quantification.     

Non-centrosymmetric Ba3Ti3O6(BO3)2

The compound previously reported as Ba₂Ti₂B₂O₉ has been reformulated as Ba₃Ti₃B₂O₁₂, or Ba₃Ti₃O₆(BO₃)₂, a new barium titanium oxoborate. Small single crystals have been recovered from a melt with a composition of BaTiO₃:BaTiB₂O₆ (molar ratio) cooled between 1100°C and 850°C. The crystal structure has been determined by X-ray diffraction: hexagonal system, non-centrosymmetric space group, a=8.7377(11) Å, c=3.9147(8) Å, Z=1, wR(F²)=0.039 for 504 unique reflections. Ba₃Ti₃O₆(BO₃)₂ is isostructural with K₃Ta₃O₆(BO₃)₂. Preliminary measurements of nonlinear optical properties on microcrystalline samples show that the second harmonic generation efficiency of Ba₃Ti₃O₆(BO₃)₂ is equal to 95% of that of LiNbO₃.     

High-yield synthesis and characterization of monodisperse sub-microsized CoFe2O4 octahedra

In this study, sub-microsized CoFe₂O₄ octahedra with a high yield are synthesized via a simple hydrothermal route under mild conditions. The as-prepared products are characterized by conventional techniques of XRD, SEM, TEM, ED and HR-TEM. The results show that the as-synthesized sample exhibits octahedral morphology with a narrow size distribution. The edge size of CoFe₂O₄ octahedra is estimated to be about 0.10-0.14 μm. The growth process is also monitored by time and temperature-dependent observation. It is found that the reaction temperature has no obvious influence on the product morphology but a significant effect on the size of CoFe₂O₄ octahedra, while the reaction time determines the final morphology of the product. Moreover, it is displayed that the citrate ions play a key role in the formation of CoFe₂O₄ octahedra. Furthermore, the possible growth mechanism of the sub-microsized CoFe₂O₄ octahedra is discussed on the basis of a series of experiments. Magnetic measurements show that sub-micro-sized CoFe₂O₄ octahedra exhibit obvious ferromagnetic behaviors. The saturation magnetization (M_s), remanent magnetization (M_r), and coercivity (H_c) are determined to be 85.8, 29.2 emu/g and 892 Oe, respectively.     

Direct and stereoselective synthesis of β-d-mannosides using 4,6-O-benzylidene-protected mannosyl diethyl phosphite as a donor

A direct and practical method for the construction of β-mannosidic linkages is described. While β-selectivities in the TMSOTf-promoted glycosidation of 2,3,4,6-tetra-O-benzyl-d-mannosyl diethyl phosphite are found to be highly dependent on the reactivity of acceptor alcohols, 2,3-di-O-benzyl-4,6-O-benzylidene-d-mannosyl diethyl phosphite reacts with a wide range of acceptor alcohols in the presence of TMSOTf in CH₂Cl₂ at −45 °C to give β-mannosides in high yields with good to high β-selectivities.     

Unprecedented InCl3-catalyzed formation of cis-fused perhydrofuro[2,3-b]oxepines

2-Methylindole and its N-substituted derivatives react smoothly with 2,3-dihydrofuran (DHF) in the presence of a catalytic amount of InCl₃ under mild conditions to afford the corresponding 2-methyl-3-perhydrofuro[2,3-b]oxepin-4-yl-1H-indole derivatives in fairly good yields with high diastereoselectivity, while 3,4-dihydro-2H-pyran (DHP) affords exclusively 5,5-di(1H-3-indolyl)-1-pentanol derivatives in high yields under similar reaction conditions.     

Expedient synthesis of 4-O-methylhonokiol via Suzuki-Miyaura cross-coupling

Concise and practical synthesis of 4-O-methylhonokiol was achieved in 34% overall yield. The key features of our synthesis include chemoselective ortho-mono bromination of phenol as well as biaryl formation via Suzuki-Miyaura cross-coupling, in which bromophenol was reacted with potassium aryltrifluoroborate using Pd(OAc)₂ and RuPhos under microwave conditions.     

A facile approach for the synthesis of 14-aryl- or alkyl-14H-dibenzo[a,j]xanthenes under solvent-free condition

A facile, efficient and environment-friendly protocol for the synthesis of 14-aryl- or alkyl-14H-dibenzo[a,j]xanthenes has been developed by one-pot condensation of 2-naphthol with aliphatic and aromatic aldehydes in the presence of P₂O₅ or InCl₃ as catalysts under solvent-free conditions. The present approach offers the advantages of clean reaction, simple methodology, short reaction time, high yield, easy purification, and economic availability of the catalyst.     

Synthesis of the repeating trisaccharide unit of the cell wall lipopolysaccharide of Escherichia coli type 8

NIS/TfOH mediated glycosidation of methyl 3,4,6-tri-O-benzyl-α-d-mannopyranoside with phenyl 2-O-acetyl-3,4,6-tri-O-benzyl-1-thio-α-d-mannopyranoside furnished the corresponding disaccharide derivative in excellent yield and α-selectivity. Zémplen deacetylation of the same followed by reaction with BSP/Tf₂O-preactivated phenyl 4,6-O-benzylidene-2,3-di-O-benzyl-1-thio-α-d-mannopyranoside generated methyl 4,6-O-benzylidene-2,3-di-O-benzyl-β-d-mannopyranosyl-(1→2)-3,4,6-tri-O-benzyl-α-d-mannopyranosyl-(1→2)-3,4,6-tri-O-benzyl-α-d-mannopyranoside in very good yield and excellent β-selectivity. Pd/C catalyzed hydrogenation of the latter finally afforded the repeating trisaccharide of Escherichia coli 8 O-antigen as its methyl glycoside.     

Synthesis and characterization of n=5, 6 members of the La4Srn−4TinO3n+2 series with layered structure based upon perovskite

Layered compounds have been synthesized and structurally characterized for the n=5 and 6 members of the perovskite-related family La₄Sr_n−4Ti_nO_3n+2 by combining X-ray diffraction and transmission electron microscopy. Their structure can be regarded as comprising [(La,Sr)₅Ti₅O₁₇] and [(La,Sr)₆Ti₆O₂₀] perovskite blocks joined by crystallographic shears along the a-axis, with consecutive blocks shifted by 1/2 [100]_p. The n=5 member is similar to the previously reported n=5 member of other A_nB_nO_3n+2-related series. The n=6 member, which has only been briefly reported in other systems previously, is also a well-behaved member of this A_nB_nO_3n+2 series.