A novel method for the reduction of sulfoxides and pyridine N-oxides with the system silane/MoO2Cl2

A novel method for the reduction of sulfoxides and pyridine N-oxides using a silane and a catalytic amount of MoO₂Cl₂ in excellent yields and with a wide functional group tolerance is reported. A green protocol for this reaction was developed in water with the air-stable catalytic system PMHS/MoO₂Cl₂(H₂O)₂.     

Reduction of sulfoxides with boranes catalyzed by MoO2Cl2

The first example of an organic reduction with boranes catalyzed by a high valent oxo-complex is reported. The systems catecholborane/MoO₂Cl₂(H₂O)₂ (5 mol %) and BH₃·THF/MoO₂Cl₂ (5 mol %) proved to be very efficient for the reduction of sulfoxides to the corresponding sulfides in excellent yields.     

MoO2Cl2 as a novel catalyst for Friedel-Crafts acylation and sulfonylation

The use of MoO₂Cl₂ as a novel catalyst for Friedel-Crafts acylation and sulfonylation is described. A series of aromatic ketones and sulfones were prepared in moderate to good yields using acyl chloride or sulfonyl chloride in the presence of MoO₂Cl₂ (20 mol %), under solvent-free conditions.     

A novel method for the reduction of alkenes using the system silane/oxo-rhenium complexes

In this work, we report the first practical application of high-valent oxo-complexes for the reduction of alkenes to the corresponding alkanes. The catalytic system Ph(Me)₂SiH/ReIO₂(PPh₃)₂ (5 mol %) proved to be very efficient for the reduction of mono- and disubstituted alkenes under solvent-free conditions.     

A novel efficient and chemoselective method for the reduction of nitriles using the system silane/oxo-rhenium complexes

This work reports the reduction of nitriles to the corresponding primary amines with silanes catalyzed by oxo-rhenium complexes. The catalytic system PhSiH₃/ReIO₂(PPh₃)₂ (10 mol %) reduced efficiently a series of nitriles in the presence of a wide range of functional groups such as -Cl, -F, -Br, -I, -CF₃, -OCH₃, -SCH₃, -SO₂CH₃ and -NHTs.     

Chemoselective hydrogenation of nitroarenes and deoxygenation of pyridine N-oxides with H2 catalyzed by MoO2Cl2

A chemoselective and highly efficient hydrogenation of nitroarenes and deoxygenation of pyridine N-oxides using a cheap and environmentally friendly H₂/MoO₂Cl₂ system has been developed     

Use of CaH2 as a reductive hydride source: reduction of ketones and imines with CaH2/ZnX2 in the presence of a Lewis acid

A new combination reagent of CaH₂/ZnX₂ effectively reduced a variety of ketones and imines to the corresponding alcohols and amines, respectively, in the presence of a catalytic amount of a Lewis acid such as Ti(O-i-Pr)₄, Al(O-i-Pr)₃, B(O-i-Pr)₃ and ZnF₂.     

Molybdenum pentachloride (MoCl5) or molybdenum dichloride dioxide (MoO2Cl2): advanced catalysts for thioacetalization of heterocyclic, aromatic and aliphatic compounds

A new, convenient and mild method for thioacetalization of heterocyclic, aromatic and aliphatic compounds catalyzed by MoCl₅ or MoO₂Cl₂ is described. This novel method is important for the synthesis of the difficult to prepare heterocyclic thioacetals such as the pterin thioacetals and it offers significant advantages such as high conversion, short reaction times and simplicity in operation.     

Binuclear oxomolybdenum(V) chlorides: Molecular structure of Mo2O4Cl2(DMF)4 and Mo2O4Cl2(bipy)2 · DMF

Reduction of MoO₂Cl₂(DMF)₂ (DMF = dimethylformamide) with PPh₃ in mild conditions afforded the dinuclear species Mo₂O₃Cl₄(DMF)₄. Related compounds could be prepared by substitution of DMF with stronger bases. While attempting to grow crystals of these compounds new complexes with the syn-[Mo₂O₄]²⁺ core were obtained. The molecular structures of Mo₂O₄Cl₂(DMF)₄, and Mo₂O₄Cl₂(bipy)₂ (bipy = 2,2′-bipyridine) have been established by X-ray diffraction analysis.     

New active-iron based reducing system for carbonyl compounds and imines. Stereoselective reduction of cyclic ketones

The reaction of different carbonyl compounds and imines with a mixture of iron(II) chloride tetrahydrate, an excess of lithium powder, and a catalytic amount of 4,4′-di-tert-butylbiphenyl (DTBB, 5 mol%) in THF at room temperature, led to the formation of the corresponding alcohols and amines, respectively. The process was also applied to the transformation of α,β-unsaturated carbonyl compounds into the corresponding saturated alcohols. The new reducing system exhibited good to excellent diastereoselectivity toward the reduction of different monocyclic and polycyclic ketones.     

1,4-Dihydropyridine/BF3OEt2 for the reduction of imines: Influences of the amount of added BF3OEt2 and the substitution at N-1 and C-4 of the dihydropyridine ring

We have evaluated four 1,4-dihydropyridines (DHPs 1a, 1b, 1c and 1d) as reducing agents, which presented free (hydrogenated) or phenyl-substituted N-1 and C-4 positions of the DHP ring. Reactions combining each of the DHP and different amounts of BF₃OEt₂ were evaluated for the reduction of imine 2a (N-benzylideneaniline). DHP simultaneously substituted at N-1 and C-4 (1a), and DHP substituted at C-4 (1b) gave lower yields for reduction of 2a in comparison with DHPs 1c and 1d (both unsubstituted at the C-4 position). By evaluating the amount of added BF₃OEt₂ to the reaction mixture, we have found that DHP 1c (substituted at N-1) provided its best yield for amine 3a (82%) when associated with stoichiometric amounts BF₃OEt₂, while DHP 1d (N-1- and C-4-unsubstituted derivative) was more effective (90% yield) with catalytic quantities of the Lewis acid. The reaction system using DHP 1c under stoichiometric BF₃OEt₂ could also be successfully applied with additional imine examples and under reductive amination conditions.     

Enantioselective addition of methyllithium to aromatic imines catalyzed by C2 symmetric tertiary diamines

Enantioselective addition of methyllithium to aromatic imines catalyzed by C₂ symmetric tertiary diamines is described. Eleven diamines have been tested, for which dramatic effect of the nitrogen substitution has been observed. Diamines bearing hindered group close to the nitrogen led to racemic product while homologous hindered diamines led to the best results. Enantiomeric excess up to 74% could be achieved. An explanation of the absolute configuration of the product obtained is given considering the mechanism of the reaction.     

Highly efficient and chemoselective reduction of sulfoxides using the system silane/oxo-rhenium complexes

This work reports a novel method for the reduction of sulfoxides with silanes catalyzed by high valent oxo-rhenium(V) and (VII) complexes. The catalytic system PhSiH₃/ReIO₂(PPh₃)₂ (1 mol %) proved to be highly efficient for the reduction of a wide range of sulfoxides in excellent yields under mild conditions. This novel methodology is also highly chemoselective, tolerating several functional groups such as –CHO, –CO₂R, –Cl, –NO₂, and double or triple bonds.     

Efficient method for the reduction of carbonyl compounds by triethylsilane catalyzed by PdCl2

The versatility of the palladium(II) chloride and triethylsilane system has been tested in the reduction of aromatic carbonyl compounds. The reaction takes place under mild conditions. This facile and efficient method affords high yields for the reduction of aldehydes and ketones to the corresponding alkanes.     

The synthesis of β-lactams via a one-pot Reformatsky reaction of imines promoted by Zn/Cp2TiCl2 (cat.)

In the presence of Zn/Cp₂TiCl₂ (cat.) α-bromoacetates, γ-bromocrotonates or α-bromomethylacrylates react with imines in one-pot to form β-lactams, 3-vinyl-β-lactams or α-methylene-γ-lactams, respectively, at room temperature without the need for pretreatment of the solvent and Zn.     

Synthesis of imines from nitrobenzene and TiO2 particles suspended in alcohols via semiconductor photocatalysis type B

UV irradiation on a non-aqueous suspension of titanium dioxide with nitrobenzene and different alcohols in deaerated conditions produces imines and aniline as main products. The conversion of nitrobenzene and the corresponding selectivity of imines or aniline depend on the type of alcohol used. A low conversion (3-12%) and selectivity close to 100% to imines were obtained with methyl, ethyl, or propyl alcohol. Otherwise, using i-propanol only aniline was detected with a conversion of 13%. Finally, a mixture of aniline and imines was formed employing n-butyl, n-amyl, and i-amyl alcohols with the higher conversion (∼50%).     

Electronic structures and X-ray photoelectron spectra of MoO2 and Li2 MoO4

Electronic structures of MoO₂ (4d²) and molybdatc (4d^o) are calculated by the discrete-variational Xα method employing [Mo₂O₁₀^12? and [MoO₄]^2? clusters. The calculations indicate that the Mo—O bond is more covalent in the molybdatc than in MoO₂. Level structures for the valence band region arc in agreement with XPS spectra of MoO₂ and Li₂MoO₄.     

The electrochemical reduction of CP2TiCl2 in the presence of trimethylphosphine

The electrochemistry of the complexes Cp₂TiCl_x(PMe₃)_2-x in anhydrous THF has been studied. The most stable complexes at the three oxidation states of titanium are Cp₂TiCl₂, Cp₂TiCl(PMe₃) and Cp₂Ti(PMe₃)₂, and each of these species is readily formed by electrolysis. It has also been demonstrated that oxidation/reduction of these species is followed by facile and rapid ligand exchange to form the preferred species in the new oxidation state provided a stoichiometric concentration of the required ligand is present. The consequences of this redox and ligand exchange chemistry for the synthetic reactions catalyzed by lower oxidation states of Ti are discussed. Finally, the voltammetry of a titanocycle is reported, and it is shown that the corresponding Ti^III metallocycle is stable.     

The compounds and the phase diagram of MoO3-Rich Bi2O3MoO3 system

The equilibrium phase diagram between 0 and slightly above 50 mole% Bi₂O₃ in the Bi₂O₃MoO₃ system has been studied by differential thermogravimetric analysis (DTA) and X-ray diffraction measurements on fused mixtures and single crystals. The results confirm the existence of the four compounds α (Bi₂O₃·3MoO₃), β (Bi₂O₃·2MoO₃), γ (Bi₂O₃·MoO)₃ and ? (～1.3Bi₂O₃·MoO₃) in the system. However, the phase diagram as well as the nature of melting of the α and γ were found disagreed with previous results. The γ compound melts incongruently at 947°C, whereas the α compound melts congruently at 662°C. The crystal class and lattice parameters of the compounds were determined based on the single crystal as well as powder pattern techniques. The results show that all four compounds have the monoclinic structure. The unit cell parameter of the β, γ, and ? compounds were found to be quite different from previously reported data. The lattice parameters obtained from X-ray analysis were also verified by density measurements of the single crystals. The polymorphism of the compounds was also investigated with single crystal samples. No polymorphic transformations for the α, β, and γ phases were detected in the work.     

Stereoselective synthesis of syn-β-amino esters using the TiCl4/R3N reagent system

The reactions of benzaldehyde imines and esters with the TiCl₄/R₃N reagent system give syn-β-amino esters as the major products in 38-87% yields.