The first asymmetric addition of organogallium to aldehydes catalyzed by chiral titanium catalysts

The addition of organogallium to aldehydes was realized with titanium tetrachloride as a Lewis acid catalyst. For the first time, the catalytic asymmetric addition of organogallium to aldehydes was investigated with chiral titanium complexes, which were formed from titanium tetrachloride and salan ligands, with mediocre to good chemical yields and enantioselectivities.     

Polystyrene-supported TiCl4 as a novel,efficient and reusable polymeric Lewis acid catalyst for the chemoselective synthesis and deprotection of 1,1-diacetates under eco-friendly conditions

Copolymer beads of styrene and divinylbenzene (5–7%) were synthesized and combined with titanium tetrachloride in CS₂ to form a stable complex. The PS/TiCl₄ complex was used as a mild and efficient polymer-supported Lewis acid catalyst for the preparation of 1,1-diacetates from various types of aldehydes under heterogeneous conditions at room temperature. Deprotection of the resulting 1,1-diacetates has also been achieved using the same catalyst in methanol. This new protocol has the advantages of easy availability, stability, reusability of the eco-friendly catalyst, high to excellent yields, chemoselectivity, simple experimental and work-up procedure. Moreover, this polymeric catalyst could be recovered easily and reused several times without significant loss in activity.     

Enantioselective cyanosilylation of aldehydes catalyzed by a novel N,N′-dioxide-Ti(OPr)4 bifunctional catalyst

A novel bifunctional asymmetric catalyst containing N-oxide and titanium(IV) was developed and applied to the asymmetric cyanosilylation of aldehydes. Optically active trimethylsilyl cyanohydrin ethers were obtained up to 99% yield and 80% ee in the presence of 5 mol % catalyst loading at −78 °C. Based on the experimental results, the catalytic cycle was proposed as a pathway in which Lewis acid and Lewis base activated aldehyde and trimethylsilylcyanide (TMSCN), respectively.     

Titanium tetrachloride incorporated crosslinked polystyrene copolymer as an efficient and recyclable polymeric Lewis acid catalyst for the synthesis of Β-amino carbonyl compounds at room temperature

An efficient and eco-friendly procedure for one-pot synthesis of β-amino carbonyl compounds by three-component reaction of aromatic aldehydes, acetophenone, and aromatic amines via a Mannich type reaction using a stable tightly bound complex, titanium tetrachloride incorporated crosslinked polystyrene copolymer (PS/TiCl₄), as a water tolerant, recoverable, and reusable polymeric Lewis acid catalyst in ethanol at room temperature is reported. The complex of the polystyrene and TiCl₄ provides a shelf-stable acidic, water tolerant material, and it is not easily hydrolyzed by water. Our findings thus show a novel and improved modification of the Mannich type reaction in terms of mild reaction conditions, clean reaction profiles, applicability to various substrates using a simple workup procedure which makes this reaction an interesting alternative to previously applied procedures. The recyclability of the catalyst makes this protocol environmentally benign.     

An efficient method for the preparation of N-phosphinoyl and N-sulphonyl imines directly from aromatic aldehydes

Reaction of phosphinamides and sulphonamides with aromatic aldehydes at 0°C in the presence of titanium tetrachloride and triethylamine provides a simple one-step preparation of N-phosphinoyl and N-sulphonyl imines.     

Synthesis of various 6-substituted 1,4,5,6-tetrahydropyridazines by substitution of a 1,4,5,6-tetrahydro-6-tosylhydrazinopyridazines

1,4,5,6-Tetrahydro-1-tosyl-6-tosylhydrazinopyridazines were prepared by reaction of a 1,4-ketoaldehyde with two equivalents of tosylhydrazine. Thus-obtained hydropyridazines were utilized as a substrate for synthesis of various 1,4,5,6-tetrahydropyridazine derivatives by activation with a Lewis acid, and various nucleophiles reacted to give the corresponding 6-substituted 1,4,5,6-tetrahydropyridazine derivatives. Self-reaction of a 1,4,5,6-tetrahydro-6-tosylhydrazinopyridazine in the presence of 0.5 equivalent of titanium tetrachloride gave a 1,4,5,6-tetrahydropyridazine bearing a pyrrole ring at the 6-position.     

SnCl4-Catalyzed Aza-Acetalization of Aromatic Aldehydes: Synthesis of Aryl Substituted 3,4-Dihydro-2H-1,3-benzoxazines

Stannic tetrachloride was an efficient Lewis acid catalyst for the aza-acetalization of aromatic aldehydes with o-arylaminomethyl phenols, and a series of novel aryl substituted 3,4-dihydro-2H-1,3-benzoxazines were prepared in good yields under mild conditions. SnCl₄ was a more efficient catalyst for the reaction than p-toluenesulfonic acid, sulfuric acid, and aluminium chloride.     

Pinacol Coupling of Aromatic Aldehydes and Ketones in Ethyl Acetate Mediated by TiCl4‐Mg

Titanium tetrachloride in ethyl acetate can be reduced by Mg powder to the corresponding low‐valent titanium complexes, which can reduce some aromatic aldehydes and ketones to the corresponding pinacols in 38–85% yields within 15–60 min at rt with stirring.     

TiCl4 and Grignard reagent-promoted ring-opening reactions of various epoxides: synthesis of γ-hydroxy-α,α-difluoromethylenephosphonates

A straightforward methodology for the synthesis of diethyl γ-hydroxy-α,α-difluoromethylenephosphonates is reported. In the presence of titanium tetrachloride, epoxide ring-opening reactions occurred upon treatment with lithium diethyl difluoromethylenephosphonate. When diethyl 3,4-epoxy-1,1-difluorobutylphosphonate was reacted with TiCl₄ and Grignard reagents, the corresponding halohydrins were obtained in very good yields.     

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.     

Chemistry of 2,5-bis(trimethylsiloxy)furans. III: Synthesis of γ-hydroxybutenolides

γ-Hydrobutenolides were obtained from the reaction of substituted 2,5- bis(trimethylsiloxy)furans with aldehydes and ketones using titanium tetrachloride activation. Similarly, α,β-unsaturated carbonyl compounds reacted as a Michael receptor with the title compounds to give γ-hydroxybutenolides.     

Ketene bis(trimethylsilyl) acetals. Cross-aldol condensation with aldehydes. Stereochemistry of the reaction

The titanium tetrachloride catalyzed condensation of the title acetals with aldehydes, leads to threo or erythro β-hydroxyacids with good stereoselectivity which depends mainly on the nature of the acetal counterion.     

Ketene bis(trimethylsilyl) acetals. Cross-aldol type condensation reactions with aldehydes and schiff bases

Condensation of the title acetals with aldehydes and Schiff bases in the presence of titanium tetrachloride is reported for the first time. It leads to β-hydroxyacids and to β-lactams via a cross-aldol type reaction, with good yields.     

超声辐射下低价钛配合物诱发芳香醛的还原偶联

超声辐射下，于二氯甲烷溶剂中，以锌粉或铝粉还原四氯化钛的四氢呋喃配合 物可生成相应的低价钛配合物，室温下此配合物可使一些芳香醛在4～25 min内还 原偶联为相应的邻二醇，收率为33％～98％．     

(Z)-Selective Wittig and Corey-Chaykovsky reactions of propargyl ylides using trialkylgallium bases

Trialkylgalliums deprotonated propargylphosphonium salts and propargylsulfonium salts to form propargyl ylides. The resulted organogallium intermediates underwent the Wittig reaction and the Corey-Chaykovsky reaction with aldehydes giving (Z)-enynes and (Z)-epoxides predominantly. The use of an appropriate trialkylgallium is essential for the stereoselectivity.     

An efficient synthesis of chiral isoquinuclidines by Diels-Alder reaction using Lewis acid catalyst

The Diels-Alder reaction of 1,2-dihydropyridine derivatives (1-phenoxycarbonyl-1,2-dihydropyridine 1 or 1-methoxycarbonyl-1,2-dihydropyridine 4) with N-acryloyl (1S)-2,10-camphorsultam (1S)-2 {or N-acryloyl (1R)-2,10-camphorsultam (1R)-2} in the presence of Lewis acid, such as titanium tetrachloride, zirconium tetrachloride, and hafnium tetrachloride afforded the endo-cycloaddition product, 2-azabicyclo[2.2.2]octane derivatives in good yields with excellent diastereoselectivity. The absolute stereochemistry assignment of the endo-cycloaddition product (1S)-5a starting from N-acryloyl (1S)-2,10-camphorsultam (1S)-2 has been established to be (1S,4R,7S) and the reaction mechanism was proposed.     

Stereoselection in the condensation between ethyl propionate and aldehydes

Ethyl propionate can be converted stereoselectively into geometrical isomers of O-ethyl-O-trimethylsilylmethylketene acetal ($\text{5}$). The E-isomer of $\text{5}$ condenses with aldehydes by titanium tetrachloride to give stereoselectively the threo isomers of ethyl 2-methyl-3-hydroxy carboxylates.     

高分子载体Lewis酸催化剂——弱碱树脂-四氯化钛复合物

<正> 高分子催化剂以许多独特的优点和功能日益受到人们的重视,我们曾将四氯化钛与聚苯乙烯反应制成一种比较稳定的复合物,它对酯化、缩醛等有机反应有良好的催化效能”,也可作为α-甲基苯乙烯正离子聚合的有效催化剂,但重复使用性能欠佳,妨碍实际应用,本文应用市售弱碱性聚苯乙烯型离子交换树脂与四氯化钛反应,制成一种更     

高分子载体Lewis酸催化剂——聚乙烯基吡咯烷酮-四氯化钛复合物

<正> 功能高分子是近年来高分子科学的一个十分活跃的领域,日益受到人们的重视,高分子催化剂是功能高分子的重要组成部分,具有许多独特的优点和功能,是目前催化剂研究的方向之一,发展迅速。 我们曾将在空气中强烈水解的Lewis酸四氯化钛与聚苯乙烯反应制备了一种高分     

Polymer-supported lewis acid catalysts. VII. Polystyrene-bonded Ti(IV) chloride catalysts

A polystyrene-bonded Ti(IV) chloride catalyst was synthesized by the reaction of a polystyryl lithium (catalyst I , PS—TiCl₂) or a polystyryl magnesium (catalyst II , PS-TiCl₃) combined with titanium tetrachloride. The catalyst produced is a polymeric organometallic compound containing 0.479 mmol Ti/g catalyst, 0.986 mmol Cl/g catalyst (catalyst I ) and 0.281 mmol Ti/g catalyst, 0.766 mmol Cl/g catalyst (catalyst II ), depending on the method of synthesis. Both catalysts showed very good stability and good catalytic activity in such organic reactions as esterification, acetalation, and ketal formation. They can be reused many times without losing its catalytic activity. © 1993 John Wiley & Sons, Inc.