Studies on Glycosides VI. Facile Synthesis of Alkyl α-and β-D-Glucopyranosides

A facile Method for the synthesis of alkyl α- and β-D-glucopyranosides using 1-0-trimethylsilyt-2,3,4,6-tetra-O-benzyl-α-D-glucopyranose by the promotion of BF₃ET₂O was reported. The mixture of α -and β-anomers, in which β-anomers predominated, was obtained in good yields.     

Synthesis and Reactivity of β-Carboline-Hydantoin Systems

The synthesis of 2,5-disubstituted 1,3-dioxo-6H-1,2,3,5,11,11a-hexahydroimidazo[1, 5-b]-β-3a-y and the reduction of carbolines 3m-r with different amounts of lithium aluminium hydride is described.     

Synthesis, Reactivity and Crystal Structure of β—Diketiminate Ytterbium Chlorides

Reaction of anhydrous YbCl3 with 1 equiv, of LLi [L=p-ClPhNC(Me)CH(Me)N(C6H3-2,6-i-Pr2)] in THF at room temperature gave the β-diketiminate lanthanide dichloride LYbCl2(THF)2 (1) in good isolated yield. Similarly reaction of anhydrous YbCl3 with 1 equiv, of LLi, then with 1 equiv, of t-BuCpNa in THF yielded the expected mixed-ligand β-diketiminate ytterbium chloride (t-BuCp)YbL(μ-Cl)2Li(THF)2 (2). Both 1 and 2 were well characterized by elemental analysis, IR spectra, ^1H NMR spectra, and X-ray diffraction analysis.     

Synthesis,Structure and Reactivity of Lanthanocene Complexes

ＩｎｔｒｏｄｕｃｔｉｏｎＴｈｅｃｈｅｍｉｓｔｒｙｏｆｏｒｇａｎｏｌａｎｔｈａｎｉｄｅｓｈａｓｅｘｐｅｒｉｅｎｃｅｄｅｘｔｒｅｍｅｌｙｉｍｐｏｒｔａｎｔｄｅｖｅｌｏｐｍｅｎｔｓｄｕｒｉｎｇｔｈｅｌａｓｔｔｗｏｄｅｃａｄｅｓ ,ａｎｄｎｕｍｅｒｏｕｓｕｎｕｓｕａｌｃｏｍｐｏｕｎｄｓｗｉｔｈｕｎｐｒｅｃｅ ｄｅｎｔｅｄｓｔｒｕｃｔｕｒｅｓａｎｄｕｎｉｑｕｅｒｅａｃｔｉｖｉｔｙｐａｔｔｅｒｎｓｈａｖｅｂｅｅｎｐｒｅｐａｒｅｄ .1ＯｒｇａｎｏｌａｎｔｈａｎｉｄｅｃｏｍｐｏｕｎｄｓｃｏｎｔａｉｎｉｎｇＬｎ—Ｃ ,…     

Modified Coumarins. 12. Synthesis of 3,4-Cycloannelated Coumarin β-D-Glucopyranosides

O--D-Glucopyranosides were synthesized using 3,4-cycloannelated hydroxycoumarins as aglycons. Phenolic hydroxyls were O-glycosylated via condensation of coumarin potassium salts with acetobromoglucose in homogeneous medium and in a liquid-liquid system using a phase-transfer catalyst.     

Soluble Bimetallic Oxoalkoxide Catalysts. IV. Ring-Opening Polymerization of β-Propiolactone

Abstract

The polymerization of β-propiolactone by aluminum-zinc oxoalkoxides corresponding to the structure has been studied. The overall kinetics of the reaction follow a first current order in monomer and a first order in catalyst. Mechanistic studies also indicate that these initiators operate through selective acyl-oxygen cleavage of the lactone ring with insertion in the aluminum-oxygen bond. Moreover, the polymerization proceeds by a perfectly “living” process.     

α-Radical Phosphines: Synthesis,Structure, and Reactivity

A series of phosphines featuring a persistent radical were synthesized in two steps by condensation of dialkyl-/diarylchlorophosphines with stable cyclic (alkyl)(amino)carbenes (cAACs) followed by one-electron reduction of the corresponding cationic intermediates. Structural, spectroscopic, and computational data indicate that the spin density in these phosphines is mainly localized on the original carbene carbon from the cAAC fragment; thus, it remains in the α-position with respect to the central phosphorus atom. The potential of these α-radical phosphines to serve as spin-labeled ligands is demonstrated through the preparation of several Au^I derivatives, which were also structurally characterized by single-crystal X-ray diffraction.     

Synthesis and Crystal Structure of β-Diketiminate Ytterbium Dichloride

The reaction of anhydrous YbCl3 with lithium β-diketiminate, LLi (L=N,Ndiphenyl-2,4-pentanediimine anion), in 1:1 molar ratio in THF gave rise to the title complex LYbCl2(THF)2 1 which has been characterized by single-crystal X-ray diffraction. It crystallizes in the orthorhombic system, space group Pna21(#33) with a=19.657(8), b=9.581(4), c=14.107(6) A,V=2656.8(18) A3, Z=4, C25H33N2O2Cl2Yb, Mr= 637.49, Dc=1.594 g/cm3, F(000)=1268.00 and μ (MoKα)=3.744mm- 1. The final R and wR are 0.031 and 0.073 for 2596 observed reflections with I ＞ 2σ(I), respectively. The X-ray crystal structure analysis revealed that the center ytterbium(Ⅲ) is bonded to two chloride anions, two oxygen atoms from two tetrahydrofuran molecules and one chelate ligand β-diketiminate to form a six-coordinate distorted octahedral geometry.     

Synthesis and Crystal Structure of β-Diketiminate Ytterbium Dichloride

1 TRODUCTIINON The monoanionic b-diketiminato ligands, [ArNC(R)CHC(R)NAr]- [1], are ideal for use with metals and have been applied for early[2] and late[3] transition metals and group 13 metal complexes[4]. These ligands have several attractive feature…     

Synthesis based on β-phenylethylamines. IX. Synthesis of sulfides of β-phenylethylamines and of N-benzyltetrahydroisoquinolines

New bimolecular sulfur-containing -phenylethylamines and N-benzyltetrahydroisoquinolines have been synthesized from formyl derivatives of diaryl sulfides. The possibility of using metals as catalysts for obtaining diaryl sulfides in the reaction of ortho-substituted benzaldehydes with SCl₂ has been shown for the first time.Institute of the Chemistry of Plant Substances, Academy of Sciences of the Republic of Uzbekistan, Tashkent, fax (3712) 89 14 75. Translated from Khimiya Prirodnykh Soedinenii, No. 5, pp. 731–735, September–October, 1995. Original article submitted November 11, 1994.     

Phase-Transfer Catalysis: Acylation of β-Dicarbonyl Compounds

The alkylation of β-dicarbonyl compounds under phase-transfer conditions has been studied in detail and, in virtually all of the reported examples, the C-alkylation products have been found to predominate.^1–6 Only when the reaction rate is slow is there any evidence for O-alkylation as, for example, when there is steric hindrance to the approach of the alkylating agent to the carbanionic centre.^1,7 There is no record, however, of the corresponding acylation reactions.     

Synthesis of β-Lactams from Acids and Imines Using Thiocarbonyldiimidazole

Thiocarbonyldiimidazole has been found to be an efficient acid activator for the synthesis of β-lactams by ketene-imine cycloaddition at room temperature. The experimental procedure is simple and results in excellent yields of the products. All products were characterized by spectral data and elemental analyses.     

Novel Heteróllylic Anions and their Vinylogues: Synthesis,Structure and Reactivity

Abstract

Heteróllylic anions, as a result of their different modes of coordination (σ and π) have proven to be versatile ligands for d- and f-block metals^[1]. In context of our work on 1, 2-diphosphaallylic anions lb and the synthesis of the corresponding vinylogous system, the 2.3,4-triphosphapentadienide 2b^[2], we became interested in the homologous systems and succeded in the isolation of the 3-arsa-2,4diphospha-pentadienide 2c in crystalline form.     

Synthesis of β-Nitroamines Using Nanocrystalline MgO

Nanocrystalline magnesium oxide (NAP-MgO) was found to be an effective heterogeneous, solid base catalyst for the direct aza-Henry reaction of nitroalkanes and various N-arylidene-4-methylbenzenesulfonamides to afford the corresponding β-nitroamines in excellent yields under mild conditions. The catalyst was recovered by simple centrifugation and reused for three cycles with consistent activity.      

Chemical Synthesis of Several 2'-O-, 3'-O-Glycosylated Diosgenyl β-D-Glucopyranosides

ABSTRACT

Six 2'-O-, 3'-O-glycosylated diosgenyl β-D-glucopyranosides (4-9), which have a typical structural pattern of diosgenyl saponins, were synthesized; their synthetic routes are discussed.     

Synthesis and Structure of Tetraphenylglycolide

1 INTRODUCTION Polylactide usually synthesized by a con-densation reaction of glycolide is a kind of use-ful medical polymer. Several structures of gly-colide derivatives have been determined by X-ray diffraction[1], and their molecular struc-tures showed the significant influence of subs-tituents on the conformation of glycolide hete-rocycle. The title glycolide derivative has beenrecently synthesized in laboratory, and its X-ray structure is presented herein to compare themolecular stru…     

High-Throughput Synthesis and Characterization of Aryl Silicones by Using the Piers–Rubinsztajn Reaction

Arylsilicones are widely exploited for their thermal and optical properties. The creation of phenylsilicone elastomers with specific physical properties is typically done by a “one-off” formulation and test process. Herein, it is demonstrated that high-throughput synthesis methods can be used to rapidly prepare a series of arylsilicone elastomers and then the relative impact of different aryl groups on their physical properties is assessed. Aromatic groups were incorporated into polydimethylsiloxane (PDMS) elastomers by exploiting the relative reactivity of different functional groups in the Piers–Rubinsztajn reaction. To analyze trends in the silicone mechanical properties as a function of increasing aryl concentration—structure/property relationships—libraries of elastomers were both quickly synthesized and characterized by using high-throughput suites starting from low viscosity silicone oils/monomers in 96-well plates. Liquid handling parameters were optimized to effectively work with the silicones. Incorporating aryl instead of alkyl crosslinkers into the PDMS backbone increased the silicone elastomer modulus by approximately 50 % (at a crosslink density of 6 %); elastomers prepared with an aromatic crosslinker with three contact points led to much higher moduli compared with those with one contact point at the same crosslink density. When located at precise rather than random points on the silicone chains, diphenylsilicones had lower moduli than analogous monophenylsilicones.     

Stereoselectivity of Reactions at the Glycoside Center of Carbohydrates: VII. Synthesis of Aryl α- and -β-D-Glucopyranosides by Helferich,Catalyzed by Boron Trifluoride Etherate

¹³C NMR spectroscopy was used to study the stereoselectivity of glycosylation of phenols with the and anomers of penta-O-acetyl-D-glucopyranose, penta-O-trifluoroacetyl-D-glucopyranose, and 2,3,4,6-tetra-O-acetyl-1-O-trifluoroacetyl-D-glucopyranose in the presence of boron trifluoride etherate at varied temperature, time, and catalyst amount. The boron trifluoride etherate-catalyzed reaction of penta-O-acetyl--D-glucopyranose and 2,3,4,6-tetra-O-acetyl-1-O-trifluoroacetyl--D-glucopyranose with phenols occurs with a high stereocontrol to give, depending on conditions, predominantly 1,2-cis- or 1,2-trans-arylglycosides. This reaction can be used for preparative synthesis of the - and -anomeric forms of glycosides of a wide range of phenols.     

Synthesis and Crystal Structure of β-Amino-α-Phenyl-α-Ferrocenylethanol

β-Amino-α-phenyl-α-ferrocenylethanol, FcC(OH)(Ph)CH₂NH₂ was prepared by the reduction of cyanohydrin trimethylsilyl ether of benzoylferrocene with lithium aluminum hydride. This new compound was characterized by elemental analysis, IR and ¹H NMR spectroscopy. The structure was also confirmed by a single crystal X-ray study. The compound crystallizes in monoclinic P2₁/c space group with unit cell dimensions: a = 12.5906(17), b = 5.9636(8), c = 19.8320(3) Å, β = 102.047(2)^∘, V = 1456.3(3) ų, Z = 4. The structure exhibits intra- and inter-molecular hydrogen bonding of the type N—H⋅ < eqid1 > ⋅O and O—H⋅ < eqid2 > ⋅N, respectively. The pattern of the inter-molecular hydrogen bonding interaction contains a 10-atom ring with two donors and two acceptors, showing a dimeric crystal packing.     

Synthesis of Methyl N‐Aryl Oxamate Using Soluble Polymer Support

A variety of methyl N‐aryl oxamates were synthesized using poly(ethylene glycol) (PEG) as a soluble polymer support and a monoproctection group with excellent yields.