Stereoselective synthesis of (E)-α-aryltellurenylvinylsilanes via hydromagnesiation reaction of alkynylsilanes

(E)-α-Aryltellurenylvinylsilanes have been synthesized stereoselectively via the hydromagnesiation of alkynylsilanes, followed by the reaction with aryltellurenyl iodides. (E)-α-Aryltellurenylvinylsilanes can undergo the cross coupling reaction with Grignard reagents in the presence of Ni(PPh₃)₂Cl₂ catalyst to afford (Z)-1,2-disubstituted vinylsilanes in good yields.     

Efficient preparation of (Z)-alkenyl derivatives from (Z)-vinyl (N,N-diisopropyl)carbamate via Ni-catalysed coupling reactions

A (Z)-vinyl (N,N-diisopropyl)carbamate treated with Grignard reagents, under Wenkert Nickel-catalysed conditions, gave access to several substituted (Z)-alkenyl derivatives. These Nickel-catalysed reactions, carried out with vinyl-, phenyl-, p-methoxyphenyl-, trimethylsilylmethylmagnesium bromide and benzylmagnesium chloride, led to the corresponding (Z)-alkenyl derivatives in good yields and high stereoselectivities.     

Stereoselective synthesis of 2-iodo-1-perfluoroalkyl-2(Z)-alkenes and E or Z-4-perfluoroalkylmethyl-4-en-2-ynol via Na2S2O4-promoted radical addition reaction of perfluoroalkyl iodides with allenes and the palladium-catalyzed kinetic resolution with Sonogashira coupling reaction

A Na₂S₂O₄-promoted radical addition reaction of perfluoroalkyl iodides with allenes has been studied in which a Z/E mixture of 2-iodo-1-perfluoroalkyl-2-alkenes 3 were afforded in 52-69% yields. A kinetic resolution using Sonogashira coupling reaction in MeCN using Et₂NH as the base was developed to synthesize the 2-iodo-1-perfluoroalkyl-2(Z)-alkenes (Z-3) and E-4-perfluoroalkylmethylalk-4-en-2-ynols (E-5) stereoselectively. A complete Sonogashira coupling procedure in Et₂NH at 40 °C was also developed affording a mixture of E and Z-4-perfluoroalkylmethyl-4-en-2-ynols (E-5 and Z-5), which may be easily separated by chromatography on silica gel.     

A novel method for (Z)-stereoselective preparation of CF3-substituted enediynes and their coupling reactions

Trifluoromethylated enynyl sulfones 3 were reacted with 2-4 equiv of phenyl, n-hexyl, trimethylsilyl, or triisopropylsilyl substituted ethynyllithium reagents in THF or ether at 0 °C to give trifluoromethylated enediynes 6 (Z)-stereoselectively in 41-96% yields. The reactions of β-fluoro-β-trifluoromethylvinyl sulfone 5 with same ethynyllithium reagents (4 equiv) afforded the corresponding enediynes 6 in 41-90% yields. The cross-coupling reactions of 6 bearing TMS group with aryl iodides in the presence of Pd(PPh₃)₂Cl₂, Ag₂CO₃, and n-Bu₄NBr provided the corresponding enediynes 6 in 20-71% yields. Dimerization of (Z)-6 bearing TMS group in the presence of CuBr₂ and K₂CO₃ yielded dimer (Z,Z)-7 in good yield.     

Novel organomagnesium reagents in synthesis. Catalytic cyclomagnesiation of allenes in the synthesis of N-, O-, and Si-substituted 1Z,5Z-dienes

An efficient method for the synthesis of valuable N-, O-, and Si-containing 1Z,5Z-diene compounds was developed. The method comprises Cp₂TiCl₂-catalyzed homo- and cross-cyclomagnesiation of 1,2-dienes by Grignard reagents (RMgR′) to give 2,5-dialkylidenemagnesacyclopentanes in up to 96% yield. This approach was successfully used in the synthesis of 5Z,9Z-dienoic acids, precursors of acetogenins and insect pheromones.     

Alteration of rare-earth-metal cluster iodides R(R6I12Z) through cation substitution

Four examples of (A_xR_1−x)R₆I₁₂Z phases further illustrate the flexibility of the rhombohedral R₇X₁₂Z structure to substitution of heterocations for the isolated R^III atoms without destruction of the structure. The examples with R=La, Pr, Z=Fe, Co, Ir, and stoichiometric amounts of A=Na or Ca were prepared by traditional high temperature techniques and characterized by single crystal and Guinier powder X-ray diffraction techniques. Product compositions refined in the parent space group from reactions of stoichiometry AR₆I₁₂Z were (Na_0.90Pr_0.10)Pr₆I₁₂Ir, (Na_0.954La_0.046)La₆I₁₂Fe, and (Ca_0.801La_0.199)La₆I₁₂Co. More general characteristics of and trends in the family of R₇X₁₂Z structures are also considered, including distortions of the ideal motif as a function of extremes in the components.     

Synthesis of D-(6R) - and D-(6S) -(6-2H1) glucose

Chemical synthesis ofD-(6R)- and D(6S)-(6-²H₁) glucose is described comprising (i) formation of 6-²H₁)-3-o-benzyl-5,6-dideoxy-l, 2-0-isopropylidene-α-D-xylo-hex-5-ynofuranose from D-glucose; (ii) stereospecific reduction of the deuterated acetylene functionality to (E)- or (Z)-deuterated olefin; (iii) stereospecific cis-dihydroxylation of the deuterated olefin; and (iv) separation of stereoisomers based on the intrinsic chirality of D-glucose and subsequent deprotection.     

Probing the reactivity of nebularine N1-oxide. A novel approach to C-6 C-substituted purine nucleosides

A novel approach to the synthesis of purine nucleoside analogues, featuring the reaction of the C6-N1-O⁻ aldonitrone moiety of 9-ribosyl-purine (nebularine) N1-oxide with some representative dipolarophiles, as well as Grignard reagents, is reported. Addition of Grignard reagents to the electrophilic C-6 carbon of the substrate allows a facile access to C-6 C-substituted purine nucleosides without using metal catalysts. 1,3-Dipolar cycloaddition processes lead to novel nucleoside analogues via opening, degradation or ring-enlargement of the pyrimidine ring of the base system of the first-formed isoxazoline or isoxazolidine cycloadduct.     

Copper(II) and iron(III) complexes of N-nitroso-N- alkylhydroxylamines,and the X-ray crystal structures of bis(N-nitroso-N-isopropylhydroxylaminato)copper(II) and tris(N-nitroso-N-propylhydroxylaminato)iron(III)

N-nitroso-N-alkylhydroxylamines have been prepared by hydrolysis of the mixture obtained by reaction of nitric oxide with Grignard reagents, and stabilized as their copper(II) or iron(III) complexes, Cu(RN₂O₂)₂ and Fe(RN₂O₂)₃, where R is, for example, Me, Et, Prⁱ, Bu^iso, Ph, n-C₈H₁₇ or n-C₁₂H₂₅. The complexes have been characterized by analytical, magnetic and spectroscopic measurements. By single-crystal X-ray methods Cu(PrⁱN₂O₂)₂ has been found to be trans-planar and Fe(PrⁿN₂O₂)₃ has a facial octahedral structure; in each complex the NO bond lengths are equal with no significant variation between the copper and iron complexes.     

Alkylimido and oxo aryls of rhenium. X-ray structures of (BuittN)2ReCl2(o-MeC6H4) and MO2(2,6-Me2C6H3)2, M = Re and Os

The compounds (Bu^tN)₃Re(aryl), (aryl = o-tol, xylyl and mes2), have been prepared from (Bu^tN)₃Re(OSiMe₃) and the appropriate Grignard reagents. The aryls have been converted to the corresponding dichloride compounds, (Bu^tN)₂ReCl₂(aryl) by treatment with HCl. The X-ray crystal structure of (Bu^tN)₂ReCl₂(o-tol) has been determined. The compound has square pyramidal geometry with one linear (basal site) and one bent (axial site) imido group, which formally suggests a 16e configuration.The interaction of xylyl magnesium bromide with [Me₃NH] [ReO₄] or Re₂O₇ gives the diamagnetic rhenium(V) complex [(xylyl)₂ReO₂]₂Mg(THF)₂, which can be oxidized to the paramagnetic rhenium compound, ReO₂(xylyl)₂. Interaction of ReO₃(OSiMe₃) with either xylyl or mesityl Grignard yields ReO₂(aryl)₂ directly in higher yield. The molecule is tetrahedral.The interaction of OsO₄ with xylyl magnesium bromide yields OsO₂(xylyl)₂. The geometries of the O₂MC₂ units in MO₂(xylyl)₂, M = Re and Os, are analogous to those found in the corresponding mesityl derivatives, with the OOsO angle much larger than the OReO angle (139° vs 121°).     

New alkali-metal-molybdenum(VI)-selenium(IV) oxides: syntheses, structures, and characterization of A2SeMoO6 (A=Na, K, or Rb)

Three new quaternary selenites, A₂SeMoO₆ (A=Na⁺, K⁺, or Rb⁺), were synthesized through the solid-state reaction of A₂MoO₄ with SeO₂ at 400°C. Although the reported materials are ‘stoichiometrically equivalent’, the compounds exhibit strikingly different crystal structures. Whereas Na₂SeMoO₆ has a three-dimensional crystal structure, K₂SeMoO₆ and Rb₂SeMoO₆ are molecular and uni-dimensional, respectively. However, all of the new materials have structures containing Mo⁶⁺ octahedra linked to Se⁴⁺ trigonal pyramids. Although the Mo⁶⁺ and Se⁴⁺ cations are in local asymmetric environments in all three materials, only Na₂SeMoO₆ is non-centrosymmetric. Single crystal X-ray data: Na₂SeMoO₆, cubic, space group, P2₁3 (no. 198), a=8.375(5) Å, Z=4, R(F)=0.0143; K₂SeMoO₆, monoclinic, space group, P2₁/c (no. 14), a=6.118(8) Å, b=15.395(2) Å, c=7.580(9) Å, β=112.39(4)°, Z=4, R(F)=0.0281; Rb₂SeMoO₆, orthorhombic, space group, Pnma (no. 62), a=7.805(9) Å, b=6.188(7) Å, c=14.405(4) Å, Z=4, R(F)=0.0443.     

A facile stereoselective synthesis of (E)‐α‐silylvinyl sulfides via hydromagnesiation of alkynylsilanes

Hydromagnesiation of alkynylsilanes 1 in diethyl ether gave (Z)‐α‐silylvinyl Grignard reagents 2 , which reacted with arylsulfenyl chlorides 3 to afford stereoselectively (E)‐α‐silylvinyl sulfides 4 in good yields. (E)‐α‐Silylvinyl sulfides 4 could undergo the cross‐coupling reactions with Grignard reagents in the presence of NiCl₂(PPh₃)₂ to give stereoselectively (Z)‐1,2‐disubstituted vinylsilanes 5 . © 2005 Wiley Periodicals, Inc. Heteroatom Chem 16:644–647, 2005; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/hc.20165     

Syntheses, structures, and vibrational spectroscopy of the two-dimensional iodates Ln(IO3)3 and Ln(IO3)3(H2O) (LnYb, Lu)

The reaction of Lu³⁺ or Yb³⁺ and H₅IO₆ in aqueous media at 180 °C leads to the formation of Yb(IO₃)₃(H₂O) or Lu(IO₃)₃(H₂O), respectively, while the reaction of Yb metal with H₅IO₆ under similar reaction conditions gives rise to the anhydrous iodate, Yb(IO₃)₃. Under supercritical conditions Lu³⁺ reacts with HIO₃ and KIO₄ to yield the isostructural Lu(IO₃)₃. The structures have been determined by single-crystal X-ray diffraction. Crystallographic data are (MoKα, λ=0.71073 Å): Yb(IO₃)₃, monoclinic, space group P2₁/n, a=8.6664(9) Å, b=5.9904(6) Å, c=14.8826(15) Å, β=96.931(2)°, V=766.99(13), Z=4, R(F)=4.23% for 114 parameters with 1880 reflections with I>2σ(I); Lu(IO₃)₃, monoclinic, space group P2₁/n, a=8.6410(9), b=5.9961(6), c=14.8782(16) Å, β=97.028(2)°, V=765.08(14), Z=4, R(F)=2.65% for 119 parameters with 1756 reflections with I>2σ(I); Yb(IO₃)₃(H₂O), monoclinic, space group C2/c, a=27.2476(15), b=5.6296(3), c=12.0157(7) Å, β=98.636(1)°, V=1822.2(2), Z=8, R(F)=1.51% for 128 parameters with 2250 reflections with I>2σ(I); Lu(IO₃)₃(H₂O), monoclinic, space group C2/c, a=27.258(4), b=5.6251(7), c=12.0006(16) Å, β=98.704(2)°, V=1818.8(4), Z=8, R(F)=1.98% for 128 parameters with 2242 reflections with I>2σ(I). The f elements in all of the compounds are found in seven-coordinate environments and bridged with monodentate, bidentate, or tridentate iodate anions. Both Lu(IO₃)₃(H₂O) and Yb(IO₃)₃(H₂O) display distinctively different vibrational profiles from their respective anhydrous analogs. Hence, the Raman profile can be used as a complementary diagnostic tool to discern the different structural motifs of the compounds.     

Palladium-catalyzed isomerization of (Z)-1-functionalized-4-acetoxy-2-butenes: Solvent and substituent effects

The Pd(PPh₃)₄-catalyzed isomerization of (Z)-1,4-diacetoxy-2-butene, (Z)-1-(t-butyldimethylsilyloxy)-4-acetoxy-2-butene and (Z)-1-(t-butyldiphenylsilyloxy)-4-acetoxy-2-butene affords the corresponding (E)-isomers and 1,2-difunctionalized-3-butenes. In THF, the formation of the (E)-isomers is mainly due to reaction from an η¹-allylpalladium intermediate while an η³-allylpalladium is the main key intermediate in DMF. The time to reach equilibrium between the products and their respective concentrations depend on the nature of the substituents and the solvent.     

Synthesis, structure of [H3dien]·(MF6)·H2O (M=Cr, Fe) and Fe Mössbauer study of [H3dien]·(FeF6)·H2O

Single crystals of [H₃dien]·(FeF₆)·H₂O (I) and [H₃dien]·(CrF₆)·H₂O (II) are obtained by solvothermal synthesis under microwave heating. I is orthorhombic (Pna2₁) with a=11.530(2) Å, b=6.6446(8) Å, c=13.787(3) Å, V=1056.3(2) Å³ and Z=4. II is monoclinic (P2₁/c) with a=13.706(1) Å, b=6.7606(6) Å, c=11.3181(9) Å, β=99.38(1)°, V=1034.7(1) Å³ and Z=4. The structure determinations, performed from single crystal X-ray diffraction data, lead to the R₁/wR₂ reliability factors 0.028/0.066 for I and 0.035/0.102 for II. The structures of I and II are built up from isolated FeF₆ or CrF₆ octahedra, water molecules and triprotonated amines. In both structures, each octahedron is connected by hydrogen bonds to six organic cations and two water molecules. The iron-based compound is also characterized by ⁵⁷Fe Mössbauer spectrometry: the hyperfine structure confirms the presence of Fe³⁺ in octahedral coordination and reveals the existence of paramagnetic spin fluctuations.     

Synthesis and reactivity of novel cationic organonickel(II) compexes. X-ray structure of [bis(2-diphenylphosphinoethyl)phenylphosphinenickel-O-methylsulfinate]tetraphenylborate

Cationic tetracoordinate nickel(II) compounds containing a nickelcarbon σ bond with general formula [NiR(etp)]Y, (etp  bis(2-diphenylphosphinoethyl)phenylphosphine, PhP(CH₂CH₂PPh₂)₂; R = CH₃, CH₂C₆H₅, C₆H₅; Y = BPh₄, PF₆) were synthesized by reaction of the complexes [NiX(etp)]Y (X = halogen) with appropriate Grignard reagents.This type of organometallic complexes undergo insertion of sulfur dioxide into the NiC bond with formation of tetracoordinate O-sulfinate derivatives of nickel(II). The structure of [NiOS(O)CH₃(etp)]BPh₄ has been determined from three dimensional X-ray data collected by counter methods. The compound crystallized in the triclinic group P$\text{1}$ with cell dimensions a 16.726(4), a 15.350(4), c 11.632(3) Å, α 66.55(4), β 73.37(4), γ 74.75(4)°, Z = 2. The structure was refined by full matrix least-squares methods to a conventional R factor of 0.076. The coordination polyhedron has a distorted square planar geometry. The sulfinate group is linked to the metal through an oxygen atom.     

Action des composes organomagnesiens sur les pyrones-2—IX : Etude des différentes voies réactionnelles

The formation of the dihydropyranol 15 during the synthesis of the 6-hydroxy-4-heptene-2-one (Z) 14 indicates the possibility of an equilibrium between ketols (Z) 5 and pyranols 6. This equilibrium lies well to the side of the pyranol. It might be argued that the dihydropyranol compounds prepared from 2-pyrones and Grignard reagents can be derived from the Z ethylenic ketols.Criteria for the reaction scheme are provided by the stereoselectivity of intermediates in agreement with MNDO (modified neglect of diatomic overlap) calculations.A brief discussion of the present knowledge on the different reaction schemes concerning the reaction of Grignard reagents with 2-pyrones is added.     

Synthesis and Structure of New BiMn2MO6 Compounds Where M=P, As, or V

The new compounds BiMn₂PO₆, BiMn₂AsO₆, and BiMn₂ VO₆ have been prepared and shown to be structurally related to several other BiA₂MO₆ compounds. The structure of BiMn₂PO₆ was refined from neutron powder diffraction data in space group Pnma with a=12.04 Å, b=5.37 Å, c=8.13 Å, and Z=4. It contains (BiO₂)¹⁻ chains and (PO₄)³⁻ tetrahedra. The observed fivefold coordination for the Mn²⁺ cations is unusual for Mn in this oxidation state.     

Sensitized photoreduction of cobalt(II) and iron(II). Structural characterization of [Co(CO)(o-C6H4[PPh2]2)2]PF6

Triplet-state ketones readily sensitized the photoreduction of bis(acetyl-acetonato)cobalt(II) or CO_solv²⁺ under atmospheric pressure of carbon monoxide to give Co(CO)₄⁻. The low-valent cobalt could be trapped and isolated as phosphine-substituted metal carbonyl complexes. The crystal structure of one of the products, [Co(CO)(o-C₆H₄[PPh₂]₂)₂]PF₆ has been determined. It is orthorhombic, space group Pbca, Z = 8, with unit cell dimensions a 19.704(5), b 24.850(13), c 21.865(9) Å. Phosphine-substituted iron(0) carbonyl complexes have also been isolated from similar photoreductions of iron(II) species.     

A novel open-framework with non-crossing channels in the uranyl vanadates A(UO2)4(VO4)3 (A=Li, Na)

A new sodium uranyl vanadate Na(UO₂)₄(VO₄)₃ has been synthesized by solid-state reaction and its structure determined from single-crystal X-ray diffraction data. It crystallizes in the tetragonal symmetry with space group I4₁/amd and following cell parameters: a=7.2267(4) Å and c=34.079(4) Å, V=1779.8(2) Å³, Z=4 with ρ_mes=5.36(3) g/cm³ and ρ_cal=5.40(2) g/cm³. A full-matrix least-squares refinement on the basis of F² yielded R₁=0.028 and wR₂=0.056 for 52 parameters with 474 independent reflections with I?2σ(I) collected on a BRUKER AXS diffractometer with MoKα radiation and a CCD detector. The crystal structure is characterized by _∞²[(UO₂)₂(VO₄)] sheets parallel to (001) formed by corner-shared UO₆ distorted octahedra and V(2)O₄ tetrahedra, connected by V(1)O₄ tetrahedra to _∞¹[UO₅]⁴⁻ chains of edge-shared UO₇ pentagonal bipyramids alternately parallel to the a- and b-axis. The resulting three-dimensional framework creates mono-dimensional channels running down the a- and b-axis formed by face-shared oxygen octahedra half occupied by Na. The powder of Li analog compound Li(UO₂)₄(VO₄)₃ has been synthesized by solid-state reaction. The two compounds exhibit high mobility of the alkaline ions within the two-dimensional network of non-intersecting channels.