2,3:4,6‐Di‐O‐isopropylidene‐α‐l‐sorbofuranose and 2,3‐O‐isopropylidene‐α‐l‐sorbofuranose

In the title compounds, C₁₂H₂₀O₆, (I), and C₉H₁₆O₆, (II), the five‐membered furanose ring adopts a ⁴T₃ conformation and the five‐membered 1,3‐dioxolane ring adopts an E₃ conformation. The six‐membered 1,3‐dioxane ring in (I) adopts an almost ideal ^OC₃ conformation. The hydrogen‐bonding patterns for these compounds differ substantially: (I) features just one intramolecular O—H...O hydrogen bond [O...O = 2.933 (3) Å], whereas (II) exhibits, apart from the corresponding intramolecular O—H...O hydrogen bond [O...O = 2.7638 (13) Å], two intermolecular bonds of this type [O...O = 2.7708 (13) and 2.7730 (12) Å]. This study illustrates both the similarity between the conformations of furanose, 1,3‐dioxolane and 1,3‐dioxane rings in analogous isopropylidene‐substituted carbohydrate structures and the only negligible influence of the presence of a 1,3‐dioxane ring on the conformations of furanose and 1,3‐dioxolane rings. In addition, in comparison with reported analogs, replacement of the –CH₂OH group at the C1‐furanose position by another group can considerably affect the conformation of the 1,3‐dioxolane ring.     

Reductive degradation of nido-1-CB8H12 into smaller-cage carborane systems via new monocarbaboranes [arachno-5-CB8H13](-) and closo-2-CB6H8

Treatment of the nido-1-CB8H12 (1) carborane with NaBH4 in THF at ambient temperature led to the isolation of the stable [arachno-5-CB8H13]- (2(-)), which was isolated as Na+[5-CB8H13]-.1.5 THF and PPh4 +[5-CB8H13]- in almost quantitative yield. Compound 2(-) underwent a boron-degradation reaction with concentrated hydrochloric acid to afford the arachno-4-CB7H13 (3) carborane in 70 % yield, whereas reaction between 2(-) and excess phenyl acetylene in refluxing THF gave the [closo-2-CB6H7]- (4-) in 66 % yield. Protonation of the Cs+4(-) salt with concentrated H2SO4 or CF3COOH in CH2Cl2 afforded a new, highly volatile 2-CB6H8 (4) carborane in 95 % yield, the deprotonation of which with Et3N in CH2Cl2 leads quantitatively to Et3NH+[2-CB6H7](-) (Et3NH+4(-)). Both compounds 4- and 4 can be deboronated through treatment with concentrated hydrochloric acid in CH2Cl2 to yield the carbahexaborane nido-2-CB5H9 (5) in 60 % yield. New compounds 2-, 3, and 4 were structurally characterised by the ab initio/GIAO/MP2/NMR method. The method gave superior results to those carried out using GIAO-HF when relating the calculated 11B NMR chemical shifts to experimental data.     

Polyhedral metallathiaborane chemistry: Synthesis and characterisation of metallathiaboranes based on the twelve-vertex icosahedral closo-{MSB10H10} unit, where M is Rh or Ir

The reaction of [nido-7-SB₁₀H₁₂] with [RhCl(PPh₃)₃] in the presence of N,N,N′N′-tetramethylnaphthalene-1,8-diamine (tmnd) in CH₂Cl₂ gives twelve-vertex [2,2-(PPh₃)₂-2-H-closo-2,1-RhSB₁₀H₁₀] (1) and eleven-vertex [8,8-(PPh₃)₂-nido-8,7-RhSB₉H₁₀] (2), as major products, plus the dimeric species [{(PPh₃)-closo-RhSB₁₀H₁₀}₂] (3) as a minor product. Reaction of 1 with PMe₂Ph in CH₂Cl₂ results in phosphine exchange and hydride substitution, affording the chloro analogue of 1, [2,2-(PMe₂Ph)₂-2-Cl-closo-2,1-RhSB₁₀H₁₀] (4). By contrast, reaction between [IrCl(PPh₃)₃] and [nido-7-SB₁₀H₁₂] in CH₂Cl₂ with tmnd affords only one product, twelve-vertex [2,2-(PPh₃)₂-2-H-closo-2,1-IrSB₁₀H₁₀] (5). [RhCl₂(η⁵-C₅Me₅)]₂ with [nido-7-SB₁₀H₁₂] under the same conditions gives twelve-vertex [2-(η⁵-C₅Me₅)-closo-2,1-RhSB₁₀H₁₀] (6). All the compounds are characterised by NMR spectroscopy, and by mass spectrometry, and the molecular structure of [2,2-(PMe₂Ph)₂-2-Cl-closo-2,1-RhSB₁₀H₁₀] (4) was established by single-crystal X-ray diffraction analysis. This last rhodathiaborane 4 is fluxional in solution through a process that involves a reversible partial rotation of the {RhCl(PMe₂Ph)₂} unit above the {SB₄} pentagonal face of the {SB₁₀H₁₀} fragment.     

Polymethylated [Fe(η6-arene)2]2+ dications: methyl-group rearrangements and application of the EINS mechanism

Reactions between the methylated arenes ArMe(n) [where ArMe(n) = C(6)Me(n)H((6-n)), and n = 1-6] and FeCl(2) in heptane at 90 °C in the presence of anhydrous AlCl(3) give, for the arenes with n = 1-5, extensive isomerisations and disproportionations involving the methyl groups on the arene rings, and the formation of mixtures of [Fe(ArMe(n))(2)](2+) dications that defy separation into pure species. GC-MS studies of AlCl(3)/mesitylene and AlCl(3)/durene reactions in the absence of FeCl(2) (90 °C, 2 h) allow quantitative assessments of the rearrangements, and the EINS mechanism (electrophile-induced nucleophilic substitution) is applied to rationalise the phenomena. By contrast, ArMe(n) / FeCl(2) /AlCl(3) reactions in heptane for 24-36 h at room-temperature proceed with no rearrangements, allowing the synthesis of the complete series of pure [Fe(ArMen)](2+) cations in yields of 48-71%. The pure compounds are characterised by (1)H NMR spectroscopy and electrospray-ionization mass-spectrometry (ESI-MS), and the structures of [Fe(m-xylene)(2)][PF(6)](2) and [Fe(durene)(2)][PF(6)](2) are established by single-crystal X-ray diffraction analyses.     

Syntheses of side-chain fluorinated biologically important imidazoles and indoles

We review in this report the preparation of several side-chain fluorinated analogues of biologically important imidazoles and indoles. The building blocks used should also have applications in other synthetic problems. The addition of “FBr” to vinyl imidazole derivatives was used to prepare β-fluoro- and β,β-difluorohistamine and histidinols, as well as β-fluorourocanic acid. Deoxyfluorination of intermediate acylindoles was used to prepare a series of β,β-difluorotryptamine derivative, including the fluorinated analogue of the important neurotransmitter, serotonin.     

Solution and particle effects on the biosorption of heavy metals by seaweed biomass

Biosorption of cadmium (Cd), cobalt (Co), copper (Cu), nickel (Ni), lead (Pb), and zinc (Zn) by six fractions of particle sizes, ranging from 0.063 to 1.4 mm of dry marine algal biomass ofSargassum fluitans andAscophyllum nodosum, is examined. Equilibrium metal uptake by larger particles was higher than that by smaller particles in the order of Pb > Cd > Cu > Co > Zn > Ni for both biomass types, withS. fluitans sorbing slightly more thanA. nodosum. Uptakes of metals ranged from the highest, q_max = 369 mg Pb/g (particle size 0.84–1.00 mm), to the low Zn and Ni uptakes, q_max = 77 mg/g (size 0.84–1.00 mm) for S.fluitans. A. nodosum adsorbed metals in the range from q_max = 287 mg Pb/g (particle size 0.84–1.00 mm) to q_max = 73 mg Zn/g (particle size 0.84-1.00mm). Harder stipe fractions of S.fluitans demonstrated generally higher metal uptakes than the softer fractions derived from its blades (leaves). The pH dependence of the Zn uptake byS. fluitans exhibited a S-shaped curve between pH 1.5 and pH 7, with 50% of the maximum (pH 7.0) uptake at pH 3.5. Monovalent Na and K ions at higher concentrations inhibited the biosorption of Zn byS. fluitans. A significant inhibition started at 50 mM potassium chloride or sodium acetate, and at 1M the biosorption was completely blocked.     

Methyl 3,3,3-trifluoropyruvate hemiaminals: Stability and transaminations

Hemiaminals of methyl 3,3,3-trifluoropyruvate with aromatic amines, benzylic monoamines and diamines were prepared and their interconversions studied using NMR spectrometry. In solution, benzylic hemiaminals were found to be stable in contrast to aromatic hemiaminals, which, in turn, were stable in the solid state.