Utilization of organogallium and organoindium compounds as alkylation reagents in organic synthesis: the addition of trialkylgallium and trialkylindium to aldehydes catalyzed by Lewis acids

The utilization of organogallium and organoindium compounds as alkylation reagents to aldehydes was realized with titanium tetrachloride as the strong Lewis acid catalyst. Furthermore, 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. Copyright © 2005 John Wiley & Sons, Ltd.     

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.     

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％．     

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.     

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.     

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.     

Knoevenagel kondensationen mit TiCl4/base-IV : Umsetzungen von aldehyden und ketonen mit phosphonoessigester und methylendiphosphonsäureestern

In the presence of titanium tetrachloride and an organic base in tetrahydrofurane, triethyl phosphonoacetic acid undergoes condensation with aliphatic and aromatic aldehydes and aromatic ketones to yield the corresponding triethyl alkylidene and arylidene phosphonoacetic acids respectively. Tetraalkyl methylenediphosphonates and aromatic or aliphatic α-branched aldehydes react under identical conditions in the same way. The largely unknown triethyl alkylidene and arylidene phosphonoacetic acids and the new tetraalkyl alkylidene and arylidene methanediphosphonic acids are easily hydrogenated either catalytically or by sodium borohydride in ethanol to give the corresponding saturated compounds in nearly quantitative yields.     

(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.     

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.     

N-Methyl-C-(trichlortitanio)formimidoylchlorid. Ein effizientes Reagenz zur Homologisierung von Aldehyden und Ketonen zu α-Hydroxy-carbonsäureamiden

N-Methyl-C-(trichlorotitanio)formimidoyl Chloride, a Highly Efficient Reagent for Homologations of Aldehydes and Ketones to α-Hydroxycarboxamides The known title compound 6 formed by addition of titanium tetrachloride to methyl isocyanide in methylene chloride adds to the carbonyl group of aldehydes and ketones. The adducts 7 are hydrolized to N-methyl-α-hydroxycarboxamides 8 which are (from ketones) or are not branched (from aldehydes) in the α-position. The yields in this new modification of the Passerini reaction are near 90%, also with readily enolized ketones such as acetone and acetophenone. In contrast to the previously used organotitanium reagents of the type RTiX₃, the preparation of the reagent 6 does not require any Li-, Mg- or Zn-derivative as a precusor.     

An improved procedure for the asymmetric aldol reaction of the titanium enolate of an N3-propionyl-3,4,5,6-tetrahydro-2H-1,3,4-oxadiazin-2-one

The direct formation of the titanium enolate of N₃-propionyl-3,4,5,6-tetrahydro-2H-1,3,4-oxadiazin-2-one has been achieved through complexation with titanium tetrachloride at 25°C, followed by deprotonation with triethylamine (−78 to 25°C). The preformed titanium enolate has been reacted with D₂O/DCl to afford deuterated derivative 6 and also reacted with a series of aromatic and aliphatic aldehydes affording aldol adducts 4a–f with crude diastereoselectivities ranging from 8:1 to 38:1.     

Lewis base activation of Lewis acids: catalytic, enantioselective vinylogous aldol addition reactions

The generality of Lewis base catalyzed, Lewis acid mediated, enantioselective vinylogous aldol addition reactions has been investigated. The combination of silicon tetrachloride and chiral phosphoramides is a competent catalyst for highly selective additions of a variety of alpha,beta-unsaturated ketone-, 1,3-diketone-, and alpha,beta-unsaturated amide-derived dienolates to aldehydes. These reactions provided high levels of gamma-site selectivity for a variety of substitution patterns on the dienyl unit. Both ketone- and morpholine amide-derived dienol ethers afforded high enantio- and diastereoselectivity in the addition to conjugated aldehydes. Although alpha,beta-unsaturated ketone-derived dienolate did not react with aliphatic aldehydes, alpha,beta-unsaturated amide-derived dienolates underwent addition at reasonable rates affording high yields of vinylogous aldol product. The enantioselectivities achieved with the morpholine derived-dienolate in the addition to aliphatic aldehydes was the highest afforded to date with the silicon tetrachloride-chiral phosphoramide system. Furthermore, the ability to cleanly convert the morpholine amide to a methyl ketone was demonstrated.     

Lewis base activation of lewis acids. Addition of silyl ketene acetals to aldehydes

The weak Lewis acid silicon tetrachloride can be activated by catalytic amounts of the chiral bisphosphoramide (R,R)-3 to form a highly reactive, chiral trichlorosilyl cation which is an extremely effective promoter of aldol addition reactions between aldehydes and silyl ketene acetals. The tert-butyldimethylsilyl ketene acetal of methyl acetate adds nearly instantaneously to aromatic and olefinic aldehydes as well as aliphatic aldehydes (albeit more slowly) with excellent enantioselectivity. The homologous tert-butyldimethylsilyl ketene acetal of tert-butyl propanoate adds with nearly exclusive anti diastereoselectivity to a similar range of aldehydes also with excellent enantioselectivity. The origin of the slower reaction rate with aliphatic aldehydes is revealed to be the formation of chlorosilyl ether adducts.     

A novel chain reaction induced by cathodic reduction. Addition of trichloromethyl anion to aldehydes or vimyl acetate

A novel chain reaction induced by cathodic reduction was found in the reaction system consisting of carbon tetrachloride, chloroform, and electrophiles such as aldehydes or vinyl acetate. The current efficiency of addition of trichloromethyl anion to electrophiles was extremely high. Synthesis of an analogue of ethyl chrysanthemate using this new reaction was also described.     

Efficient synthesis of benzo[g]-and benzo[h]chromene derivatives by one-pot three-component condensation of aromatic aldehydes with active methylene compounds and naphthols

A convenient procedure is reported for the synthesis of benzo[g]-and benzo[h]chromene derivatives via one-pot three-component condensation of aromatic aldehydes with malononitrile or ethyl cyanoacetate and 1-or 2-naphthol in the presence of 10 mol % of titanium tetrachloride as catalyst. The reactions require no solvent; they are characterized by simple experimental procedure and easy isolation and can be performed on enlarged scale. Published in Russian in Zhurnal Organicheskoi Khimii, 2006, Vol. 42, No. 12, pp. 1824–1826. The text was submitted by the authors in English.     

Diastereoselektive synthese neuartiger Mannich-Basen mittels titanderivaten,vorläufige mitteilung

Diastereoselective Synthesis of Novel Mannich (Bases¹) through Titanium Reagents Trichlorotitanium dialkylamino-alkoxides ( 2 ; titanates of N, O-hemiacetals) are generated either from the corresponding lithium alkoxides and titanium tetrachloride (Scheme 1) or by addition of trichloro-dialkuylamino-titanium to aldehydes. The electrophilic (dialkylamino) alkylating reagents 2 are used to convert lithium enolates to β-dialkylamino-ketones and -esters 5 (Mannich bases), see Scheme 2 and Table. One diastereoisomer of the products 5g–5p thus obtained with cyclohexenolate is formed preferentially (66-84%). The configuration of the products of this first diastereoselective version of the Mannich reaction could not yet be determined. A typical procedure for carrying out the reaction is given.     

Catalytic, enantioselective alpha-additions of isocyanides: Lewis base catalyzed Passerini-type reactions

[reaction: see text] The generality of catalytic, enantioselective alpha-additions of isocyanides to aldehydes has been demonstrated (Passerini-type reactions). The catalytic system of silicon tetrachloride and a chiral bisphosphoramide (R,R)-1b provided high yields and good to excellent enantioselectivities for the addition of tert-butyl isocyanide to a wide range of aldehydes (aromatic, heteroaromatic, olefinic, acetylenic, aliphatic). Aqueous workup afforded the alpha-hydroxy tert-butyl amides whereas a low-temperature methanol quench followed by basic workup afforded the alpha-hydroxy methyl esters. The reaction is also successful for other isocyanides, albeit with reduced enantioselectivity. Reaction conditions, particularly the rate of addition of the isocyanide was found to be crucial for good yields and high selectivities.     

The first catalytic,asymmetric alpha-additions of isocyanides. Lewis-base-catalyzed,enantioselective Passerini-type reactions

The first, catalytic, enantioselective alpha-additions of isocyanides to aldehydes have been demonstrated (Passerini-type reactions). The catalytic system of silicon tetrachloride and a chiral bisphosphoramide 5a provided high yields and good to excellent enantioselectivities for the addition of tert-butyl isocyanide to a wide range of aldehydes (aromatic, olefinic, acetylenic, aliphatic). Aqueous workup afforded the alpha-hydroxy tert-butyl amides, whereas methanolic quench followed by basic workup afforded the alpha-hydroxy methyl esters.     

Synthesis of tetrakis(triethylsiloxy)titanium and tetrakis(triethylsiloxy)tin

Summary By the metathetic reaction of sodium triethylsiloxide with titanium tetrachloride and with tin tetrachloride, tetrakis(triethylsiloxy)titanium and tetrakis(triethylsiloxy)tin were synthesized.