The first example of γ-chloromagnesio γ-lactones: their generation from γ-tolylsulfinyl γ-lactones with isopropylmagnesium chloride, stability, and reaction with electrophiles

The treatment of γ-lactones having a sulfinyl group at the γ-position, which were synthesized from 1-chlorovinyl p-tolyl sulfoxides with lithium enolate of carboxylic esters, with isopropyl magnesium chloride in THF at −78 °C gave γ-chloromagnesio γ-lactones by the sulfoxide-magnesium exchange reaction in high yields. The generated γ-chloromagnesio γ-lactones were found to be stable at below −50 °C for at least 2 h. The reaction of these γ-chloromagnesio γ-lactones with electrophiles and the stereochemistry of the reactions were investigated.     

Preparation of perfluorocyclopentenylmetal species and their cross-coupling reaction with electrophiles—Remarkable accesses to versatile perfluorocyclopentene derivatives

On treating perfluorocyclopentene with bis(tributylstannyl)cyanocuprate in THF at −78 °C for 1 h, perfluorocyclopentenylstannane was obtained in good yield. The reaction of the fluorinated vinylstannane with n-BuLi in THF at −78 °C for 1 h, followed by addition of carbonyl compounds, gave the corresponding allyl alcohols in good yields. On the other hand, Pd(0)-catalyzed cross-coupling reaction of perfluorocyclopentenylstannane with benzyl chloroformate in THF at reflux temperature for 2 h proceeded smoothly to form the decarbonated coupling product in high yield.     

DTBB-catalysed lithiation of 1,2-bis(phenylsulfanyl)ethene: does 1-lithio-2-phenylsulfanylethene really exist?

The reaction of (Z)- or (E)-1,2-bis(phenylsulfanyl)ethene (1) with an excess of lithium and a catalytic amount of 4,4′-di-tert-butylbiphenyl (DTBB, 2.5 mol%) in the presence of a carbonyl compound as electrophile (Barbier conditions) in THF at −78 °C leads, after hydrolysis with water at temperatures ranging between −78 °C and rt, to a mixture of the corresponding (Z/E)-unsaturated 1,4-diols 2, the diastereomers ratio being independent of the stereochemistry of the starting materials. Allylic alcohols 3 are the main by-products, resulting from a lithium-hydrogen exchange on some of the lithiated intermediates along the whole process. A mechanistic explanation for the observed behaviour is given.     

One-pot oxidative carbon-carbon bond formation of 3-benzylic and 3-allylic indoles with carbon nucleophiles

Indolenines were generated at −78 °C from 3-benzylic or 3-allylic indoles by dehydrogenation with N-tert-butylbenzenesulfinimidoyl chloride, and a carbon-carbon bond was formed at −78 °C in a one-pot manner by treating these indolenines with various carbon nucleophiles such as active methylene compounds or organocuprates.     

The first example of direct cyclopropylation of arylamines at the 2-position with magnesium cyclopropylidenes

Treatment of magnesium cyclopropylidenes, which were generated from 1-chlorocyclopropyl phenyl sulfoxides with isopropylmagnesium chloride in THF at −78 °C, with N-lithio arylamines gave arylamines cyclopropylated at the 2-position in moderate to good yields. Use of the magnesium cyclopropylidenes having at least one substituent was found to be essential to this cyclopropylation. This procedure offers a novel synthesis of arylamines having a cyclopropane ring at the 2-position directly from arylamines.     

Structure and high-temperature thermoelectric properties of SrAl2Si2

Single crystals of SrAl₂Si₂ were synthesized by reaction of the elements in an aluminum flux at 1000 °C. SrAl₂Si₂ is isostructural to CaAl₂Si₂ and crystallizes in the hexagonal space group P-3m1 (90 K, a=4.1834 (2), c=7.4104 (2) Å, Z=1, R1=0.0156, wR2=0.0308). Thermal analysis shows that the compound melts at ∼1020 °C. Low-temperature resistivity on single crystals along the c-axis shows metallic behavior with room temperature resistivity value of ∼7.5 mΩ cm. High-temperature Seebeck, resistivity, and thermal conductivity measurements were made on hot-pressed pellets. The Seebeck coefficient shows negative values in entire temperature range decreasing from ∼−78 μV K⁻¹ at room temperature to −34 μV K⁻¹ at 1173 K. Seebeck coefficients are negative indicating n-type behavior; however, the temperature dependence is consistent with contribution from minority p-type carriers as well. The lattice contribution to the thermal conductivity is higher than for clathrate structures containing Al and Si, approximately 50 mW cm⁻¹ K, and contributes to the overall low zT for this compound.     

Alkenylation of thiophenes at the 2-position with magnesium alkylidene carbenoids

Treatment of magnesium alkylidene carbenoids, generated from 1-chlorovinyl p-tolyl sulfoxides with isopropylmagnesium chloride at −78 °C in toluene, with 2-lithiothiophenes gave 2-alkenylated thiophenes in good to high yields. The intermediate of this reaction was found to be an alkenylmagnesium, which could be trapped with iodoalkanes and ethyl chloroformate. This procedure offers a novel and efficient one-pot synthesis of thiophenes having a disubstituted or a trisubstituted olefin at the 2-position from thiophenes in good yields.     

A highly stereoselective construction of 1,2-trans-β-glycosidic linkages capitalizing on 2-azido-2-deoxy-d-glycosyl diphenyl phosphates as glycosyl donors

The scope of TMSOTf-promoted glycosidation of 2-azido-2-deoxyglycopyranosyl diphenyl phosphates is investigated. The 3,4,6-tri-O-benzyl-protected glucosyl and galactosyl donors and the 4,6-O-benzylidene-protected galactosyl donor each react with a range of acceptor alcohols in the presence of a stoichiometric amount of TMSOTf in propionitrile at −78 °C to afford 1,2-trans-β-linked disaccharides in high yields with α:β ratios ranging from 9:91 to 1:>99, regardless of the anomeric composition of the donor used. The use of propionitrile as a solvent at −78 °C has proven to be among the best choice for the highest levels of β-selectivity reported to date for this type of glycosidation. A plausible reaction mechanism, which features a large equilibrium preference for α-glycosyl-nitrilium ions over β-nitrilium ions, is proposed based on byproducts formed through their intermediacy and accounts for the observed excellent β-selectivities.     

Lithium enolates from a (−)-quinic acid-derived cyclohexanone with a β-alkoxy leaving group: regioselective preparation and evaluation of enolate stability towards β-elimination

Deprotonation of a (−)-quinic acid-derived ketone {(2S,3S,4aR,8R,8aS)-8-[(tert-butyl(dimethyl)silyl)oxy]-2,3-dimethoxy-2,3-dimethylhexahydro-1,4-benzodioxin-6(5H)-one} using lithium hexamethyldisilazide (LHMDS) at −78 °C gave one regioisomeric enolate. The regiocontrol is governed by the axial β-silyloxy substituent and the resulting lithium enolate is stable towards β-elimination at temperatures up to −40 °C. It was found that the axial β-silyloxy group could be conveniently eliminated using 2.1 equiv of LHMDS at 0 °C for 1 h and that an equatorial β-alkoxy group was much more resistant to β-elimination. A chiral lithium amide base was used to overturn the inherent regioselectivity of ketone deprotonation with LHMDS.     

One-pot dehydrogenation of carboxylic acid derivatives to α,β-unsaturated carbonyl compounds under mild conditions

Carboxylic acid derivatives such as N-acyl-2-oxazolidones, δ-lactones, and δ-lactams were smoothly dehydrogenated to the corresponding α,β-unsaturated carbonyl compounds in one-pot manner at −78 °C just by treating their lithium enolates with N-tert-butylbenzenesulfinimidoyl chloride.     

Synthesis, crystal structure and thermal behavior of Sr3B2SiO8 borosilicate

Single crystals of Sr₃B₂SiO₈ were obtained by solid-state reaction of stoichiometric mixture at 1200 °C. The crystal structure of the compound has been solved by direct methods and refined to R1=0.064 (wR=0.133). It is orthorhombic, Pnma, a=12.361(4), b=3.927(1), c=5.419(1) Å, V=263.05(11) Å³. The structure contains zigzag pseudo-chains running along the b axis and built up from corner sharing (Si,B)−O polyhedra. Boron and silicon are statistically distributed over one site with their coordination strongly disordered. Sr atoms are located between the chains providing three-dimensional linkage of the structure.The formation of Sr₃B₂SiO₈ has been studied using annealing series in air at 900-1200 °C. According powder XRD, the probe contains pure Sr₃B₂SiO₈ over 1100 °C. The compound is not stable below 900 °C. In the pseudobinary Sr₂B₂O₅-Sr₃B₂SiO₈ system a new series of solid solutions Sr_3−xB₂Si_1−xO_8−3x (x=0-0.9) have been crystallized from melt. The thermal behavior of Sr₃B₂SiO₈ was investigated using powder high-temperature X-ray diffraction (HTXRD) in the temperature range 20-900 °C. The anisotropic character of thermal expansion has been observed: α_a= −1.3, α_b=23.5, α_c=13.9, and α_V=36.1×10⁻⁶ °C⁻¹ (25 °C); α_a= −1.3, α_b=23.2, α_c=5.2, and α_V=27.1×10⁻⁶ °C⁻¹ (650 °C). Maximal thermal expansion of the structure along of the chain direction [0 1 0] is caused by the partial straightening of chain zigzag. Hinge mechanism of thermal expansion is discussed.     

Expedient synthesis of 1-vinylpyrrole-2-carbaldehydes

1-Vinylpyrrole-2-carbaldehydes and 1-vinyl-4,5-dihydrobenzo[g]indole-2-carbaldehyde were synthesized in 56-91% yields from their 1-vinyl derivatives by a modified Vilsmeier-Haack reaction. A low temperature (−78 °C) is required to avoid removal of the N-vinyl group, whereas at elevated temperature (reflux in 1,2-dichloroethane) the latter process leads to direct conversion of 1-vinylpyrroles to pyrrole-2-carbaldehydes.     

Sol-gel synthesis and characterization of LiNO3-Al2O3 composite solid electrolyte

Composite solid electrolytes in the system (1 − x)LiNO₃-xAl₂O₃, with x = 0.0-0.5 were synthesized by sol-gel method. The synthesis carried out at low temperature resulted in voluminous and fluffy products. The obtained materials were characterized by X-ray diffraction, differential scanning calorimetry, scanning electron microscopy/energy dispersive X-ray, Fourier transform infrared spectroscopy and AC impedance spectroscopy. Structural analysis of the samples showed base centred cell type of point lattice of LiNO₃ for the composite samples with x = 0.1-0.2 and body centred cell for the sample with x = 0.3. A trace amount of α-LiAlO₂ crystal phase was also present in these composite samples. The thermal analysis showed that the samples were in a stable phase between 48 °C and 230-260 °C. Morphological analysis indicated the presence of amorphous phase and particles with sizes ranging from micro to nanometre scale for the composite sample with x = 0.1. The conductivities of the composites were in the order of 10⁻³ and 10⁻² S cm⁻¹ at room temperature and 150 °C, respectively.     

Arene-promoted lithiation of 1,n-dihaloalkanes (n=2-6): a comparative study

The reaction of 1,n-dichloroalkanes 3a (n=2-6) with an excess of lithium powder and a catalytic amount of 4,4′-di-tert-butylbiphenyl (DTBB; 2.5 mol %) in the presence of different carbonyl compounds [Bu^tCHO, PhCHO, Et₂CO, (CH₂)₄CO, (CH₂)₅CO, (CH₂)₇CO, (−)-menthone], in THF at −78 °C leads, after hydrolysis with water, to the expected 1,(n+2)-diols 4, yields being <25% for n=2, 3 and in the range of 45-79% for n=4-6. When the same protocol is applied to 1,n-bromochloroalkanes 3b and 1,n-dibromoalkanes 3c (n=2-6), diols 4 are obtained in general with lower yields.     

A mild and practical method for the regioselective synthesis of N-acylated 3,4-dihydropyrimidin-2-ones. New acyl transfer reagents

The treatment of 3,4-dihydropyrimidin-2-ones with n-BuLi at −78 °C, followed by quenching with various electrophiles furnished N3-substituted derivatives, regioselectively. Further, N1,N3-diacyl derivatives were found to transfer N1-acyl groups to nucleophilic sites.     

Direct alkenylation of arylamines at the ortho-position

Treatment of magnesium alkylidene carbenoids, which were generated from 1-chlorovinyl p-tolyl sulfoxides with isopropylmagnesium chloride at −78 °C in toluene, with N-lithio arylamines gave ortho-alkenylated arylamines in moderate to good yields. The reaction was found to proceed in a highly stereospecific manner at the carbenoid carbon. This reaction offers a quite novel and direct alkenylation of arylamines at the ortho-position of the aromatic ring.     

Synthesis, crystal structure and physico-chemical properties of the new quaternary oxide Sr5BiNi2O9.6

A new black quaternary oxide Sr₅BiNi₂O_9.6 was synthesized by solid state reaction at 1200 °C. Its structure was solved by electron crystallography and X-ray powder refinement, yielding a tetragonal structure with space group I4/mmm, a=5.3637 (2) Å, c=17.5541(5) Å, Z=4. The structure can be described as a stacking of (Bi,Sr)-O rocksalt slabs and SrNiO_3−δ perovskite slabs. The initial nickel valence is close to +3.1. Thermogravimetry and high-temperature oxygen coulometry showed that this compound has variable oxygen content as a function of temperature and oxygen pressure, and ultimately decomposes when heated in low oxygen pressure above 800 °C. It is a metallic conductor with n-type conduction. Its thermoelectric power was determined and found to be −20 and −38 μV/K at 300 and 650 °C, respectively. Magnetic measurements confirm the nickel valence close to +3 and show evidence of magnetic ordering at 20 K.     

Reaction of magnesium alkylidene carbenoids with lithium acetylides and lithium thiolates: a novel synthesis of conjugated enynes and vinyl sulfides

Magnesium alkylidene carbenoids were generated from 1-chlorovinyl p-tolyl sulfoxides with i-PrMgCl at −78 °C in THF or toluene via the sulfoxide-magnesium exchange reaction. Reaction of the generated magnesium alkylidene carbenoids with lithium acetylides or lithium thiolates gave conjugated enynes or vinyl sulfides, respectively, in moderate to good yields. The intermediate of this reaction was found to be the alkenyl anion and it could be trapped with some electrophiles to give tetra-substituted conjugated enynes and vinyl sulfides.     

Selective synthesis of 2-substituted pyridine N-oxides via directed ortho-metallation using Grignard reagents

Addition of i-PrMgCl to pyridine N-oxides in THF at −78 °C generates selectively an ortho-metallated species, which can be trapped with various electrophiles to generate 2-substituted pyridine N-oxides. Furthermore, by applying a double metal-catalyzed cross-coupling, direct arylation of the pyridine N-oxides is achieved.     

Reaction of magnesium cyclopropylidene with N-lithio arylamines: a method for generation of α-amino-substituted cyclopropylmagnesiums and a study for their reactivity with electrophiles

Magnesium cyclopropylidene was generated from 1-chlorocyclopropyl phenyl sulfoxide with i-PrMgCl in THF at −78 °C in high yield by a sulfoxide-magnesium exchange reaction. The generated magnesium cyclopropylidene was found to be reactive with N-lithio arylamines to give α-amino-substituted cyclopropylmagnesiums. The reaction of the α-amino-substituted cyclopropylmagnesiums with several electrophiles was examined and a new method for a synthesis of cyclopropane amino acid derivatives was realized.