Unusual reactions of Grignard reagents toward fluoroalkylated esters

Fluorine-containing esters were demonstrated to be convenient substrates for construction of the corresponding ketones by low temperature reaction with Grignard reagents followed by warming up to 0 °C, while heating the mixture up to 80 °C readily promoted the reduction of the ketones obtained by the generated magnesium alkoxides whose mechanism was speculated as Meerwein-Ponndorf-Verley type reduction by computational technique.     

Magnesium-oppenauer oxidation of alcohols to aldehydes and ketones

Using a magnesium-Oppenauer oxidation aldehydes and ketones are prepared from halomagnesium alkoxides, which in turn are the products of Grignard reactions.     

Rearrangement of N-tert-butanesulfinyl α-halo imines with alkoxides to N-tert-butanesulfinyl 2-amino acetals as precursors of N-protected and N-unprotected α-amino carbonyl compounds

Reaction of N-tert-butanesulfinyl α-halo imines with alkoxides afforded new N-tert-butanesulfinyl 2-amino acetals in good to excellent yield. These N-tert-butanesulfinyl 2-amino acetals are convenient precursors for the TMSOTf-promoted synthesis of the corresponding N-protected α-amino aldehydes and ketones, as well as for the HCl-promoted synthesis of 2-amino acetal hydrochlorides and α-amino ketone and α-amino aldehyde hydrochlorides in high yield. Via this method, an asymmetric synthesis of (S)-cathinone hydrochloride (er 94:6) was achieved.     

Symbiotic reagent activation: Oppenauer oxidation of magnesium alkoxides by silylglyoxylates triggers second-stage aldolization

The treatment of silylglyoxylates with magnesium alkoxides at ambient temperature results in symbiotic Oppenauer oxidation of the alkoxide and Meerwein-Ponndorf-Verley reduction of the silylglyoxylate. The reduced silylglyoxylate undergoes subsequent [1,2]-Brook rearrangement and aldol reaction with the carbonyl oxidation product. The magnesium alkoxide may be accessed via deprotonation of primary or secondary alcohols with EtMgBr, via addition of Grignard reagents to aldehydes, or via CuI-catalyzed alkylation of epoxides. For aliphatic primary alkoxides, moderate levels of anti diastereoselection are observed. A crossover experiment reveals that dissociation of the nascent aldehyde from the magnesium center is faster than [1,2]-Brook rearrangement and aldolization.     

Direct observation of beta-aryl eliminations from Rh(I) alkoxides

beta-Aryl eliminations from a series of rhodium(I) alkoxides to form rhodium aryl complexes and free ketones are reported. Tertiary phenylmethoxide complexes [Rh(PEt3)n(OCPhRR')] (n = 2, 3) were prepared via alcoholysis of {Rh(PEt3)2[N(SiMe3)2} by the corresponding alcohols HOCPhRR' in the presence and absence of added PEt3. Heating of these complexes in the presence of added PEt3 generated the rhodium phenyl complex, (PEt3)3RhPh, and the corresponding ketones in good to high yields. Kinetic results are most consistent with irreversible beta-phenyl elimination from a bisphosphine-ligated rhodium alkoxide complex. Such bisphosphine complexes result from ligand dissociation from the trisphosphine complexes and have been isolated in some cases. The bisphosphine complexes are stabilized by Rh-Cphenyl interactions, as evidenced by an X-ray structure, and this structure with a metal-aryl interaction likely illustrates the pathway for C-C bond cleavage.     

Structural features and reactivity of (sparteine)PdCl2: a model for selectivity in the oxidative kinetic resolution of secondary alcohols

The chiral ligand (-)-sparteine and PdCl(2) catalyze the enantioselective oxidation of secondary alcohols to ketones and thus effect a kinetic resolution. The structural features of sparteine that led to the selectivity observed in the reaction were not clear. Substitution experiments with pyridine derivatives and structural studies of the complexes generated were carried out on (sparteine)PdCl(2) and indicated that the C(1) symmetry of (-)-sparteine is essential to the location of substitution at the metal center. Palladium alkoxides were synthesized from secondary alcohols that are relevant steric models for the kinetic resolution. The solid-state structures of the alkoxides also confirmed the results from the pyridine derivative substitution studies. A model for enantioinduction was developed with C(1) symmetry and Cl(-) as key features. Further studies of the diastereomers of (-)-sparteine, (-)-alpha-iso- and (+)-beta-isosparteine, in the kinetic resolution showed that these C(2)-symmetric counterparts are inferior ligands in this stereoablative reaction [Mohr, J. T., Ebner, D. C., and Stoltz, B. M. Org. Biomol. Chem. 2007, 5, 3571-3576].     

Unsaturated nitriles: stereoselective MgO eliminations

Alpha,beta-unsaturated nitriles are readily synthesized by eliminating MgO from beta-hydroxynitriles. Deprotonating acyclic, and cyclic, beta-hydroxynitriles with excess MeMgCl smoothly generates dianion intermediates that eject MgO with concurrent formation of alpha,beta-unsaturated nitriles. Alternatively, sequential addition of lithioacetonitrile and MgBr(2) to aldehydes and ketones generates magnesium alkoxides in situ that eliminate MgO upon addition of MeMgCl. The MeMgCl-induced MgO eliminations smoothly generate alpha,beta-unsaturated nitriles from hindered ketones that are otherwise difficult to synthesize.     

Quantum chemical modeling of chiral catalysis. Part 8. On the conformational freedom of the ketone of ketone-borane complexes of oxazaborolidines used as catalysts in the enantioselective reduction of ketones

Standard ab initio molecular orbital methods were employed to study conformational freedom of the ketone of ketone-borane complexes of chiral oxazaborolidines used as catalysts for the enantioselective reduction of ketones (CBS reduction). A formaldehyde-borane complex of 1,3,2-oxazaborolidine was used as a model system. A new conformation was found which was energetically more advantageous than the original one predicted by Corey et al. The new conformation was predicted to be destabilized by bulky substituents at the C-5 of the ring. A new class of potential oxazaborolidine catalysts for the enantioselective reduction of ketones was invented.     

A practical method for synthesis of terminal 1,2-diols in high enantiomeric excess via oxazaborolidine-catalyzed asymmetric reduction

Asymmetric borane reduction of α-hydroxy ketones protected with a tetrahydropyranyl (THP) group catalyzed by Corey's CBS reagent using N-phenylamine–borane complexes as the hydride source provided the corresponding terminal 1,2-diols with a very high enantiomeric excess.     

Organic reaction pathways in the nonaqueous synthesis of metal oxide nanoparticles

Nonaqueous-solution routes to metal oxide nanoparticles are a valuable alternative to the known aqueous sol-gel processes, offering advantages such as high crystallinity at low temperatures, robust synthesis parameters and ability to control the crystal growth without the use of surfactants. In the first part of the review we give a detailed overview of the various solution routes to metal oxides in organic solvents, with a strong focus on surfactant-free processes. In most of these synthesis approaches, the organic solvent plays the role of the reactant that provides the oxygen for the metal oxide, controls the crystal growth, influences particle shape, and, in some cases, also determines the assembly behavior. We have a closer look at the following reaction systems in this order: 1) metal halides in alcohols, 2) metal alkoxides, acetates, and acetylacetonates in alcohols, 3) metal alkoxides in ketones, and 4) metal acetylacetonates in benzylamine. All these systems offer some peculiarities with respect to each other, providing many possibilities to control and tailor the particle size and shape, as well as the surface and assembly properties. In the second part we present general mechanistic principles for aqueous and nonaqueous sol-gel processes, followed by the discussion of reaction pathways relevant for nanoparticle formation in organic solvents. Depending on the system several mechanisms have been postulated: 1) alkyl halide elimination, 2) elimination of organic ethers, 3) ester elimination, 4) C--C bond formation between benzylic alcohols and alkoxides, 5) ketimine and aldol-like condensation reactions, 6) oxidation of metal nanoparticles, and 7) thermal decomposition methods.     

树状功能高分子负载锡配合物的合成及其催化酮的Baeyer-Villiger氧化反应性能研究

通过固相合成方法将聚酰胺-胺树状分子担载于氯球上,对其外围分别用2,4-二羟基苯甲醛和邻羟基苯甲醛进行修饰,再与SnCl2.2H2O反应,形成配体不同的两类树状高分子锡配合物.将此类配合物用作30%的双氧水氧化酮的Baeyer-Villiger反应的非均相催化剂,具有较好的催化活性.2-金刚烷酮、环己酮、3-甲基-2-戊酮等都转化为相应的酯和内酯,底物的转化率和产物选择性均较高.对2-羟基苯甲醛、2,4-二羟基苯甲醛和邻羟基苯甲醛修饰的不同类型催化剂催化下的反应进行比较,发现配体对锡的担载量和催化活性均有不同程度的影响.其中邻羟基苯甲醛修饰的配合物因具有较高的锡担载量而具有了最佳的催化活性.此催化体系使用环境友好的低浓度双氧水为氧化剂,催化剂制备方法简单、催化反应完成时间短、催化剂在多次重复利用后活性没有明显降低,可回收和重复利用.     

Solid Phase Catalytic Oxidation of Alcohols by Polymer Supported Rare Earth Catalysts

Oxidation of alcohols to the corresponding aldehydes or ketones is one of the most fundamental reactions in organic chemistry [1,2]. Some of the products of the oxidation exhibit an important role in the organic synthesis as well as pharmaceutical synthesis. In most reactions, the lanthanide complexes show satisfied catalytic activities for some compounds. Furthermore, there has been increasing interest in the lanthanide complexes and several reports have appeared in the literature [3, 4]. But the exploitation of these complexes for the oxidation of some organic substrates has been limited. Here we reported a method for the preparation and the catalytic properties as well as the recycling of lanthanide complexes in oxidation of alcohols.The synthetic procedure for the polymer supported lanthanide complexes is shown as following(scheme 1):●-NH2+CICH2COOH(C2Hs)3N→●-NHCH2COOHM=Ce(Ⅲ), Tb(Ⅲ), Sm(Ⅲ)scheme 1The oxidation of benzyl alcohol was carried out in the presence of iodosylbenzene by the polymer supported Ce(Ⅲ), Tb(Ⅲ) and Sm(Ⅲ) catalysts at 80℃ for 4.0h, the yields of benz-aldehyde are as following (table 1):Table 1 Oxidation of benzyl alcohol with the supported catalysts**Reaction condition: benzyl alcohol 0.1 mmol, iodosylbenzene 0.15mmol,catalyst 0.2mg, 80℃ for 4.0h in 1,2-dichloroethane.It can be seen from the table that the Tb(Ⅲ) complex shows higher catalytic activity for the oxidation of benzyl alcohol. Further investigation is now being carded on to optimize the results.     

Stable dimeric magnesium(I) compounds: from chemical landmarks to versatile reagents

The chemistry of the s-block metals is dominated by the +1 oxidation state for the Alkali metals (group 1) and the +2 oxidation state for the Alkaline Earth metals (group 2). In recent years, a series of stable dimeric magnesium(I) compounds has been prepared and their chemistry has started to develop. These complexes feature "deformable" Mg-Mg single bonds and are stabilised by sterically demanding and chelating anionic N-ligands that prevent their disproportionation. They have rapidly proven useful in organic and organometallic/inorganic reduction reactions as hydrocarbon soluble, stoichiometric, selective and safe reducing agents. The scope of this perspective focuses on stable molecular compounds of the general type LMgMgL and describes their synthesis, structures, theoretical and spectroscopic studies as well as their further chemistry. Also, comparisons are drawn with related complexes including magnesium(II) hydrides and dimeric zinc(I) compounds.     

β-Cleavage of Bis(homoallylic) Potassium Alkoxides. Preparation of 3-Hydroxypropyl and 4-Hydroxybutyl Propenyl Ketones from γ- and δ-Lactones. Synthesis of (±)-Rose oxide

Starting from γ- and δ-lactones 1 – 3 , a two-step preparation of 3-hydroxypropyl and 4- hydroxybutyl propenyl ketones 10 – 18 is described, involving as the key step the β-cleavage of the bis(homoallylic) potassium alkoxides 4a – 9a . The novel methodology is illustrated by a short synthesis of (±)-rose oxide( 20 ).     

Direct synthesis of p-nitrobenzoic acid and benzoic acids from benzyl ketones and acetophenones using the CAN/HOAc system

The synthesis of p-nitrobenzoic acid and benzoic acids from benzyl and methyl ketones has been described using cerium(IV) ammonium nitrate in acetic acid. This simple method for the oxidation of benzylic ketones can be used as a practical method for the synthesis of 4-nitrobenzoic acid.     

Mechanism of meerwein-pondorf-verley type reductions

The reduction of benzophenone by lithium and chloromagnesium alkoxides has been studied as well as the transformation of certain lithium alkoxides to the corresponding ketones by electron transfer. Fluorenone was reduced by lithium sec-butoxide to the corresponding lithium ketyl to the extent of 65%. Lithium 9-fluoroenolate underwent in tetrahydrofuran a spontaneous transformation to lithium fluorenone ketyl. This process was interpreted as involving 1,2-hydrogen shift in an oxygen-centred radical. A mechanism for the Meerwein-Pondorf-Verley-type reductions is proposed, invoking single electron as well as 1,2-hydrogen shift steps.     

Reactions of Magnesium and Titanium Alkoxides. Preparation and Characterization of Alkoxy-Derived Magnesium Titanate Powders and Ceramics

The interaction between magnesium and titanium alkoxides is studied in order to chose the best precursors for synthesis of MgTiO₃. No reaction between magnesium and titanium methoxides and isopropoxides occurs. The solubility diagrams for Mg(OR)₂-Ti(OR)₄-ROH, R = Et,-Bu at 20°C are studied. Magnesium ethoxotitanates of variable composition Mg_nTi_4-n (OEt)_16-2n2nEtOH (n=2.0-0) which are structural analogs of Ti₄(OR)₁₆ (R = Me, Et) are isolated. This is a quite unusual example of statistical distribution of heteroatoms in molecular structures of metal alkoxides. Among the systems of metal alkoxides with simple aliphatic radicals only Mg(OBu)₂-Ti(OBu)₄-BuOH gives a convenient precursor for the synthesis of MgTiO₃. A simple scheme of preparation of magnesium titanate from the alkoxide solutions is suggested. The phase purity of MgTiO₃ is to a considerable extent dependent on the hydrolysis conditions. The alkoxy-derived magnesium titanate is obtained in the form of a uniform fine powder, it can be sintered into dense ceramics in the temperature range of 1140–1220°C which is 150–200°C lower in comparison with the conventional powders.     

New insights in the search for chiral Brønsted bases

The concept of using chiral bases in asymmetric synthesis appeared with the emergence of the chemistry of chiral lithium amides. In recent years, new classes of chiral bases, such as chiral magnesium bisamides and chiral alkali alkoxides have proven to be highly efficient and easy to handle. This paper highlights recent advances and new concepts in the chemistry of this second generation of chiral bases.     

Schiff base complexes and their versatile applications as catalysts in oxidation of organic compounds: part I

Schiff bases and their complexes are good candidates as versatile compounds which are synthesized by the condensation of a primary amino compound with either aldehydes or ketones for a variety of industrial applications. They can act as catalysts in the catalytic oxidation of organic compounds. Recent researches in oxidation catalysis have focused on how to employ the metal‐catalyzed oxidation of organic substrates. This review summarizes the current developments of the last few decades for the oxidations of organic compounds that proceed through Schiff base complexes. The chemical syntheses of Schiff bases and their complexes are outlined.     

Synthesis of unsaturated tertiary amines and α-allyl substituted ketones from azomethines using metal complex catalysts

A method has been developed for the regioselective synthesis of unsaturated tertiary amines via the reaction of magnesium amides, derived from Schiff bases, with allylic electrophiles in the presence of Pd and Cu complexes. The reaction of ketimines which have been metallated using magnesium amide with functionalized allylic compounds is catalyzed by Pd complexes and leads to the formation of -allyl substituted ketones with high regioselectivity.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 1, pp. 155–160, January, 1990.