McMurry coupling of aryl aldehydes and imino pinacol coupling mediated by Ti(O-i-Pr)4/Me3SiCl/Mg reagent

Ti(O-i-Pr)₄/Me₃SiCl/Mg reagent mediated McMurry coupling of aryl aldehydes to biaryl olefins at near room temperature. This low valent titanium (LVT) reagent also mediated the coupling of aldimines to 1,2-diamines (imino pinacol coupling).     

Reductive Coupling of Aldehydes,Ketones and Aroyl Chlorides Induced by LVT Prepared from TiCl4/Al System

Aluminium powder has been used to reduce titanium tetrachloride to generate the low valent titanium (LVT)reagent which can induce the reductive coupling of aldehydes and ketones to form the corresponding pinacols or olefins. However, arylsulfonyl chlorides will give diaryldisulfides under the same condition.     

超声波作用下羰基化合物的还原偶联反应

超声波在一些有机反应中有明显的促进作用「“，Luche等认为超声波的作用有两种主要类型［’j．一类是涉及电子转移的自由基或离子一自由基型反应，由于超声波的空化作用所产生的局部高温高压可以促进电子转移，从而明显地加快反应速度；对大多数离子型反应，超声波只能起到机械的物理作用．我们曾报道偕二卤化合物在Li、Na、Mg等金属作用下产生卡宾的反应是单电子转移过程，该反应可由于超声辐射而大大加速［‘］；而在芳基叔脚的断裂反应中，超声波可以促进三苯基俄与金属馊反应生成二苯基脚负离子，但对它进一步的亲核取代反应却没有明…     

低价钛诱导的芳香邻二酮及α-羟基酮的还原偶联反应

Treatment of aromatic 1 , 2-diketones or aromatic a-hydroxy ketones with an activated low-valent titanium reagent, prepared by reduction of TiCl3·1/3AlCl3 with a Zn-Cu reagent, gave an intermolecular coupling reaction leading to the (Z)-1, 2.3.4-tetraaryl-2-butenes. Apossible coupling reaction process was proposed for the aromatic a-hydroxy ketones.     

Reductive Coupling of Alkyl Selenocyanates to Diselenides Utilizing Environmentally Benign TiCl4-NEt3 Reagent

The reduction of TiCl4 to low valent titanium (LVT) species and the synthetic utility of such species are welldocumented chemistry of wide interest. [1] Generally, reducing agents such as Mg, Zn, Li, Sm, Pb-Te and LiAlH4are used for reduction of TiCl4.[2]     

Synthetic Reactions Using Low‐valent Titanium Reagents Derived from Ti(OR)4 or CpTiX3 (X = O‐i‐Pr or Cl) in the Presence of Me3SiCl and Mg

In the presence of Me₃SiCl, Ti(OR)₄ or CpTiX₃ (X = O‐i‐Pr or Cl) is reduced by Mg powder in THF to gradually generate a specific low‐valent titanium (LVT) species that mediates several synthetic reactions. The LVT‐catalyzed C–O bond‐cleaving reactions of allyl and propargyl ethers and esters generate parent alcohols and carboxylic acids, respectively. O‐allyl and propargyl carbamates are also readily deprotected by the LVT to afford parent amines. In addition, the respective reductive N–S or O–S bond cleavage of sulfonamides or sulfonyl esters mediated by the LVT was developed as a novel facile deprotection method. The reagent catalyzes intra‐ and intermolecular alkyne or alkyne/nitrile cycloaddition to produce substituted benzenes and pyridines, while epoxides and oxetanes are reduced to alcohols via an LVT‐mediated homolytic ring opening. The McMurry coupling of aryl aldehydes and ketones proceeds with the LVT under homogeneous and mild reaction conditions and is effective for the polymerization of aromatic dialdehydes, generating conjugated polymers. Finally, imino‐pinacol coupling of imines is mediated by the LVT to provide 1,2‐diamines.     

Selective cleavage of allyl and propargyl ethers to alcohols catalyzed by Ti(O-i-Pr)4/MXn/Mg

[reaction: see text] Allyl and propargyl ethers were effectively deallylated or depropargylated to the parent alcohols via a C-O bond cleavage catalyzed by a low-valent titanium reagent (LVT), Ti(O-i-Pr)4/TMSCl/Mg or Ti(O-i-Pr)4/MgBr2/Mg, under mild reaction conditions. Differentiation between the allyl and propargyl ethers was achieved by the reaction in the presence of AcOEt as an additive. The reagent also catalyzed intra- and intermolecular cyclotrimerization reactions of alkynes to substituted benzenes.     

Titanium promoted reduction of imines with Grignards,silanes, and zinc: identification of a new mechanism with silanes

Aldimines react with reducing agents, such as Grignards, phenylsilane or zinc in the presence of titanium(IV) isopropoxide to form amines and reductively coupled imines (diamines). Using deuterium labeled reagents, the mechanism of reduction to form amines is described. Reducing agents, such as the Grignard and zinc result in the formation of low valent titanium (LVT), which in turn reduces the imine. On the other hand, phenylsilane reacts by a distinctly different mechanism and where a hydrogen atom from silicon is directly transferred to the titanium coordinated imine.     

Characterization of silylated Ti-grafted HMS catalyst and its excellent epoxidation performance

Silylated Ti-grafted hexagonal mesoporous silica (HMS) catalyst was prepared by the chemical vapor deposition (CVD) using TiCl4 as titanium source and hexamethyldisilazane (HMDSZ) as silylating agent. The samples were characterized by XRD, N2- adsorption, FTIR, 29Si NMR, DR UV-vis, and evaluated by epoxidation of styrene, propylene, cyclohexene, and 1-hexene with cumene hydroperoxide (CHP) as oxidant, respectively. It is revealed that the catalyst possesses typical mesoporous structure, high hydrophobicity and highly dispersed tetracoordinated titanium sites and hence exhibits excellent performance in epoxidation of olefins.     

给电子体在制备烯烃聚合NdCl_3载体催化剂中的作用

<正> Martin以无水稀土氯化物为载体,与磷酸三丁酯(TBP)在庚烷溶剂中反应制得LnCl_3/TBP/TiCl_4载体催化剂,其中以NdCl_3为载体的催化剂对乙烯聚合有很高活性,但对TBP的作用和载钛结构涉及较少。NdCl_3为链状晶体结构,不同于层状晶体结构的MgCl_2和TiCl_3(α和δ型)。我们对NdCl_3/EtOH/TiCl_4催化剂进行了较为详细的研究,并与MgCl_2/EtOH/TiCl_4催化剂进行比较,发现NdCl_3载体催化剂与MgCl_2载体     

低价钛促进的1,2-二氢喹唑啉-4(3H)-酮的合成

喹唑啉-4(3H)-酮是一类生物碱,取代喹唑啉-4(3H)-酮具有广泛的药理学活性．因而对其合成方法和合成新型喹唑啉-4(3H)-酮的衍生物的研究已成为热点．低价钛试剂是一种还原偶联试剂,它能引起醛酮的还原偶联生成烯烃,还能引起其它官能团的还原偶联反应,该反应已应用于天然产物和一些碳环化合物的合成,而用于杂环化合物的合成研究报道较少．本文报道低价钛试剂(TiCl4-Zn体系)促进的1,2-二氢喹唑啉-4(3H)-酮的合成。     

Couplage des sulfones allyliques avec des reactifs de grignard en presence de cuivre synthese d'olefines

A convenient synthesis of di- and trisubstituted olefins using the coupling of Grignard reagents with allylic sulphones in the presence of copper II acetylacetonate is reported. The influence of sulphone, Grignard reagent and solvent on the regio- and stereoselectivity is discussed.     

低价钛引起的邻硝基苯甲酰胺与酮的还原成环反应

报道了TiCl₄-Sm体系引起的邻硝基苯甲酰胺与酮的反应.研究发现,邻硝基苯甲酰胺与酮还原成环生成1,2-二氢喹唑啉-4(3H)-酮.产物的结构通过元素分析、IR、¹HNMR谱和单晶X射线衍射法确定.     

TiCl4-n-Bu4NX (X = I, Br, and Cl) combination-induced coupling of alpha,beta-unsaturated ketones with aldehydes.

A three-component coupling reaction between vinyl ketones, aldehydes, and halides has been developed with TiCl(4)-n-Bu(4)NX combined reagents. Treatment of vinyl ketones with a TiCl(4)-n-Bu(4)NI combination followed by an addition of a variety of aldehydes provides syn-alpha-iodomethyl-beta-hydroxy ketones with high stereoselectivity. Methyltriphenylphosphonium iodide as well as n-Bu(4)NI acts efficiently as a halide source. The combination of TiCl(4)-n-Bu(4)NBr provides the corresponding bromo compounds in good yields. syn-alpha-Chloromethyl-beta-hydroxy ketones are obtained with the TiCl(4)-n-Bu(4)NCl combination. A competitive experiment reveals that the order of relative reactivity of the combinations is TiCl(4)-n-Bu(4)NI > TiCl(4)-n-Bu(4)NBr > TiCl(4)-n-Bu(4)NCl.     

On the electrodeposition of titanium in ionic liquids

The ability to electrodeposit titanium at low temperatures would be an important breakthrough for making corrosion resistant layers on a variety of technically important materials. Ionic liquids have often been considered as suitable solvents for the electrodeposition of titanium. In the present paper we have extensively investigated whether titanium can be electrodeposited from its halides (TiCl(4), TiF(4), TiI(4)) in different ionic liquids, namely1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)amide ([EMIm]Tf(2)N), 1-butyl-1-methylpyrrolidinium bis(trifluoromethyl-sulfonyl)amide ([BMP]Tf(2)N), and trihexyltetradecyl-phosphonium bis(trifluoromethylsulfonyl)amide ([P(14,6,6,6)]Tf(2)N). Cyclic voltammetry and EQCM measurements show that, instead of elemental Ti, only non-stoichiometric halides are formed, for example with average stoichiometries of TiCl(0.2), TiCl(0.5) and TiCl(1.1). In situ STM measurements show that-in the best case-an ultrathin layer of Ti or TiCl(x) with thickness below 1 nm can be obtained. In addition, results from both electrochemical and chemical reduction experiments of TiCl(4) in a number of these ionic liquids support the formation of insoluble titanium cation-chloride complex species often involving the solvent. Solubility studies suggest that TiCl(3) and, particularly, TiCl(2) have very limited solubility in these Tf(2)N based ionic liquids. Therefore it does not appear possible to reduce Ti(4+) completely to the metal in the presence of chloride. Successful deposition processing for titanium in ionic liquids will require different maybe tailor-made titanium precursors that avoid these problems.     

Dependence of the Reactivities of Titanium Enolates on How They Are Generated: Diastereoselective Coupling of Phenylacetic Acid Esters Using Titanium Tetrachloride

Oxidative coupling of phenylacetic acid esters was easily achieved by treating the esters with TiCl(4) and then adding Et(3)N to the resulting solution. The products consisted of dl- and meso-2,3-diphenylsuccinic acid esters with the Claisen condensation product, and the ratio of these products depended on the reaction conditions. Reaction conditions suitable for high dl selectivity were determined, and a dimer of titanium enolate was postulated as an intermediate responsible for the high dl selectivity. The selectivities were compared with those in known oxidative couplings in which titanium enolate intermediates are prepared through lithium enolates and silyl enol ethers. The results suggest that the reactivities of titanium enolates intermediates depend on how they are generated.     

Quantum chemistry study on the reactivity of PhOTiCl2CH2Cl and Cl3TiCH2Cl cyclopropanation reagents with olefins

In order to explore the new and efficient cyclopropanation reagents, a theoretical investigation of the cyclopropanation reactions of titanium carbenoid PhOTiCl₂CH₂Cl and Cl₃TiCH₂Cl with olefins was given at the B3LYP level of theory. All of the reactions examined displayed similar concerted mechanisms for the cyclopropanation of these reagents. The reactions are predicted to be highly chemical reactivity with low barriers and could be favored in experiment, and the cyclopropanation reaction proceed easily at lower temperature. The computational results are briefly compared to other carbenoid reactions and related species.     

3-对甲氧基苯基-和3-对羟基苯基-1-氨基-3a,4,5,9b-四氢化-9b-羟基-3H-环戊烯并[a]萘-2-甲腈的合成和晶体结构

用低价钛试剂(TiCl₄-Zn)与2-氰基-3-对甲氧基苯基-3-(1-四氢萘酮-2-基)丙腈反应合成了3-对甲氧基苯基-1-氨 基-3a,4,5,9b-四氢化-9b-羟基-3H-环戊烯并[a]萘-2-甲腈和3-对羟基苯基-1-氨基-3a,4,5,9b-四氢化-9b-羟基-3H-环戊烯并[a]萘-2-甲腈, 并用X射线衍射分析确定了这两个产物的结构.     

Simple alkenes as substitutes for organometallic reagents: nickel-catalyzed, intermolecular coupling of aldehydes, silyl triflates, and alpha olefins

A nickel-catalyzed method for the three-component coupling of alkenes (ethylene and alpha olefins), aldehydes, and silyl triflates is described, and this process represents the first catalytic method for coupling aldehydes and alkenes to give allylic alcohol derivatives. Conceptually, the alkene functions as a replacement for an alkenylmetal reagent.     

Allylic Functionalization of Unactivated Olefins with Grignard Reagents

New advances in the functionalization of unactivated olefins with carbon nucleophiles have provided more efficient and practical approaches to convert inexpensive starting materials into valuable products. Recent examples have been reported with stabilized carbon nucleophiles, tethered carbon nucleophiles, diazoesters, and trifluoromethane donors. A general method for functionalizing olefins with aromatic, aliphatic, and vinyl Grignard reagents was developed. In a one‐pot process, olefins are oxidized by a commercially available reagent to allylic electrophiles, which undergo selective copper‐catalyzed allylic alkylation with Grignard reagents. Products are formed in high yield and with high regioselectivity. This was utilized to synthesize a series of skipped dienes, a class of compounds that are prevalent in natural products and are difficult to synthesize by known allylic alkylation methods.