Tetraalkylammonium reactions with

A mild and effective method for obtaining N- acyl- and N- alkyl-pyrroles and -indoles is to carry out these reactions under phase-transfer conditions (80JOC3172). For example, A-benzenesulfonylpyrrole is best prepared from pyrrole under phase-transfer conditions rather than by intermediate generation of the potassium salt (81TL4901). In this case the softer nature of the tetraalkylammonium cation facilitates reaction on nitrogen. The thallium salts of indoles prepared by reaction with thallium(I) ethoxide, a benzene-soluble liquid. 

Electronegatively substituted acetylenes, such as dimethyl acetylenedicar-boxylate, do not react under normal conditions but will add the elements of hydrogen fluoride by reaction with fluoride ion (e g, CsF or tetraalkylammonium dihydrogen trifluoride) and a proton source under phase-transfer conditions [49, 50] (equation 8)... 

Extractive alkylation is used to derivatize acids, phenols, alcohols or amides in aqueous solution [435,441,448,502]. The pH of the aqueous phase is adjusted to ensure complete ionization of the acidic substance which is then extracted as an ion pair with a tetraalkylammonium hydroxide into a suitable immiscible organic solvent. In the poorly solvating organic medium, the substrate anion possesses high reactivity and the nucleophilic displacement reaction with an alkyl halide occurs under favorable conditions. 

The reverse reaction in which thioacetamide is initially alkylated and then reacted under phase-transfer catalytic conditions with the acyl halide results in the formation of A-acylthioamidates (Scheme 4.15), with only trace amounts of the S-alkyl thioesters [35], S-Alkyl thioacetates have also been obtained from trifluoro-methylsulphonyloxy compounds upon reaction with potassium thioacetate in the presence of TDA-1 [61]. It is probable that tetraalkylammonium salts would be equally good catalysts. 

For further contributions on the dia-stereoselectivity in electropinacolizations, see Ref. [286-295]. Reduction in DMF at a Fig cathode can lead to improved yield and selectivity upon addition of catalytic amounts of tetraalkylammonium salts to the electrolyte. On the basis of preparative scale electrolyses and cyclic voltammetry for that behavior, a mechanism is proposed that involves an initial reduction of the tetraalkylammonium cation with the participation of the electrode material to form a catalyst that favors le reduction routes [296, 297]. Stoichiometric amounts of ytterbium(II), generated by reduction of Yb(III), support the stereospecific coupling of 1,3-dibenzoylpropane to cis-cyclopentane-l,2-diol. However, Yb(III) remains bounded to the pinacol and cannot be released to act as a catalyst. This leads to a loss of stereoselectivity in the course of the reaction [298]. Also, with the addition of a Ce( IV)-complex the stereochemical course of the reduction can be altered [299]. In a weakly acidic solution, the meso/rac ratio in the EHD (electrohy-drodimerization) of acetophenone could be influenced by ultrasonication [300]. Besides phenyl ketone compounds, examples with other aromatic groups have also been published [294, 295, 301, 302]. 

Arylalkenes [23] and alkenes with electron withdrawing substituents [24] can be bis-alkylated across the alkene bond by electrochemical reaction with dflialoal-kanes giving 3- to 6-membered carbocyclic products in good yields. ITie best reaction conditions use an undivided cell with a nickel cathode and a sacrificial aluminium anode in dimethylformamide or N-methylpyrrolidone containing a tetraalkylammonium salt. Anodically generated aluminium ions are essential for the reaction. 1,2-Disubstituted alkenes, regardless of their stereochemistry, are converted to the tranj-substituted cycloalkane. 

The use of /i-ketocstcrs and malonic ester enolates has largely been supplanted by the development of the newer procedures based on selective enolate formation that permit direct alkylation of ketone and ester enolates and avoid the hydrolysis and decarboxylation of ketoesters intermediates. Most enolate alkylations are carried out by deprotonating the ketone under conditions that are appropriate for kinetic or thermodynamic control. Enolates can also be prepared from silyl enol ethers and by reduction of enones (see Section 1.3). Alkylation also can be carried out using silyl enol ethers by reaction with fluoride ion.31 Tetraalkylammonium fluoride salts in anhydrous solvents are normally the... 

The chemical reactions of M(BH )4 complexes have received very little attention. Both compounds behave as Lewis adds in reactions with tetraalkylammonium and lithium tetrahydroborates, yielding [(C8Hi7)3NPr][M(BH4)5], [NBu4][M(BH4)5] and LiM(BH4)5.620 Zr(BH4)4 reacts with LiAlH4 in ether to give Zr(AlH4)4, an unstable white solid, which decomposes within several hours at room temperature to a pyrophoric black solid.617... 

Oxidation with permanganate588 592 636 637 usually requires the use of a suitable solvent mixture, such as aqueous THF,638 which dissolves both permanganate and the alkene. Better results may be obtained by phase-transfer agents.440 Reaction with tetraalkylammonium permanganate may allow selective cleavage of a phenyl-substituted double bond in dienes.639... 

Iron halides react with halide salts to afford anionic halide complexes. Because iron(III) is a hard acid, the complexes that it forms are most stable with F and decrease in both coordination number and stability with heavier halides. No stable I complexes are known. [FeF5(H20)]2 is the predominant iron fluoride species in aqueous solution. The [FeF6]3 ion can be prepared in fused salts. Whereas six-coordinate [FeClJ3 is known, four-coordinate complexes are favored for chloride. Salts of tetrahedral [FeClJ can be isolated if large cations such as tetraphenylarsonium or tetraalkylammonium are used. [FeBrJ is known but is thermally unstable and disproportionates to iron(II) and bromine. Complex anions of iron(II) halides are less common. [FeClJ2 has been obtained from FeCl2 by reaction with alkali metal chlorides in the melt or with tetraethylammonium chloride in deoxygenated ethanol. 

Solvent effects in electrochemistry are relevant to those solvents that permit at least some ionic dissociation of electrolytes, hence conductivities and electrode reactions. Certain electrolytes, such as tetraalkylammonium salts with large hydrophobic anions, can be dissolved in non-polar solvents, but they are hardly dissociated to ions in the solution. In solvents with relative permittivities (see Table 3.5) s < 10 little ionic dissociation takes place and ions tend to pair to neutral species, whereas in solvents with 8 > 30 little ion pairing occurs, and electrolytes, at least those with univalent cations and anions, are dissociated to a large or full extent. The Bjerrum theory of ion association, that considers the solvent surrounding an ion as a continuum characterized by its relative permittivity, can be invoked for this purpose. It considers ions to be paired and not contributing to conductivity and to effects of charges on thermodynamic properties even when separated by one or several solvent molecules, provided that the mutual electrostatic interaction energy is < 2 kBT. For ions with a diameter of a nm, the parameter b is of prime importance ... 

Halide ion Y" in the form of soluble tetraalkylammonium salts can in some cases displace halide ion X forming a mixed-halogen adduct. However, the method has met with variable success. It is successful with tetrahaloborate ions (80) and with Me3N BI3 (9). A similar reaction with insoluble silver halides or pseudohalides has also given mixed adducts (43). 

Simple 2,2-dibutyl-l,3,2-dioxastannolanes form solid complexes of monomer units with certain nucleophiles, such as pyridine and dimethyl sulfoxide, that have 1 1 stoichiometry and pentacoordinate tin atoms.62 Such complexes are less stable for more-substituted stannylene acetals, such as those derived from carbohydrates.62 Unfortunately, the precise structures of these complexes have not yet been defined. Addition of nucleophiles to solutions of stannylene acetals in nonpolar solvents has been found to markedly increase the rates of reaction with electrophiles,63 and transient complexes of this type are likely intermediates. Similar rate enhancements were observed in reactions of tributylstannyl ethers.57 Tetrabu-tylammonium iodide was the nucleophile used first,57 but a wide variety of nucleophiles has been used subsequently tetraalkylammonium halides, jV-methylimidazole,18 and cesium fluoride64,65 have been used the most. Such nucleophilic solvents as N,N-dimethylformamide and ethers probably also act as added nucleophiles. As well as increasing the rates of reaction, in certain cases the added nucleophiles reverse the regioselectivity from that observed in nonpolar solvents.18,19... 

Aliphatic nitroso compounds can be prepared from IV-alkylhydroxylamines by oxidation with bromine, chlorine or sodium hypochlorite in weakly acidic solution, by reaction with potassium dichromate in acetic or sulfuric acid, and by oxidation with yellow mercury(II) oxide in suspension in an organic solvent. Silver carbonate on (Telite has also been used to prepare aliphatic nitroso compounds, such as ni-trosocyclohexane, in high yield from the corresponding hydroxylamines. Aqueous sodium periodate and tetraalkylammonium periodates, which are soluble in organic solvents, are the reagents most commonly used for the oxidation of hydroxamic acids and / -acylhydroxylamines to acylnitroso compounds (40). These compounds are rarely isolated, but are useful as highly reactive dienophiles in the Diels-Alder reaction. ... 

When acylnitroso derivatives are employed as dienophiles in the cycloaddition, the re-gioselectivity of the reaction is inverted with respect to the mode of addition of nitrosobenzene. Thus l,2-dihydro-A -methoxycarbonylpyridine. by reaction with V-acylhydroxylamines in the presence of tetraalkylammonium periodate at 78 r C in dichloromethane, leads to the corresponding 2-oxa-3,5-diazabicyclo[2.2.2]oct-7-enes in good yield. The regiochemistry of the cycloaddition product 2 was determined by 13C NMR84-86. 

Tetraalkylammonium hypophosphites (TAHPs), as reported by Jang and coworkers, were prepared by mixing the tetraalkylammonium hydroxide with aqueous H3P02, both of which are mild and efficient reagents for the radical deoxygenation of alcohols and formation of carbon-carbon bonds in water without the need for additives such as surfactants.10,14 Cyclododecyl S-methyldithiocarbonate has been utilised as a model compound. The reaction of... 

Among Group B systems are tetraalkylammonium (mainly, tetrabutylammonium) salt solutions in aprotic solvents (B-1) and in mixtures of an aprotic and protic solvent (B-2). In these systems the cathodic reduction of all the solution s components is appreciably retarded, while the electrons generated at the cathode disappear in the course of a homogeneous reaction with the cations of the background electrolyte or the solvent s molecules. 

The existence of ylids in the decomposition of tetraalkylammonium salts has received some attention in recent years, but only in reactions with organometallic reagents has their presence been demonstrated ,32,156)... 

A simple synthesis of 1,3,5-trichloro-l A4,2,4.6-thiatriazine (1) is by treatment of sodium or tetraalkylammonium dicyanamide with thionyl chloride.910 Originally, this reaction was described in 1970 and the product was thought to be jV -chloro-A/-(chlorosulfanyl)-/V-cyano-carboximidic chloride.60 The reaction is carried out with a great excess of thionyl chloride in the presence of a catalytic amount of dimethylformamide. The first reaction step consists of the formation of the thionyl chloride-dimethylformamide complex and reaction with the dicyanamide anion. The second step is a further sulfinylation with elimination of sulfur dioxide.32... 

Poly(2-alkyl oxazoline)s having methacrylate or acrylate end groups were prepared by two methods [182]. a) Living polyoxazoline chains, prepared using methyl p-toluene sulphonate as initiator, were end-capped by reaction with metal salts or tetraalkylammonium salts of acrylic or methacrylic acid or a trialky-lammonium salt or trimethylsilyl ester of methacrylic acid (functional termination). b) The living polymers were terminated with water in the presence of Na2C03 to provide hydroxyl-terminated chains. Subsequent acylation with acry-loyl or methacryloyl chloride in the presence of triethylamine led to the formation of the macromonomers. The procedures are outlined in the following Scheme 51. 

We found (18, 19) that ion pairing is one of the most important factors that influence the competition between reduction and substitution. Ion pairing usually depresses the rate of these SNAr reactions because free alkoxide ions display a superior reactivity, although the opposite situation was found in some instances (21). Examples of rate enhancements observed upon addition of cation complexing agents or tetraalkylammonium ions are reported in Table I. The use of n-Bu4NBr, for example, allows one to obtain substitution products in good yields and convenient times in reactions with otherwise poorly reactive alkoxides. 

More recently, quaternary organic tetraalkylammonium hydroxides have been grafted on to an MTS surface by reaction with 3-trimethoxysilyl(trimethyl)ammo-nium chloride then treatment of the resulting solid with a methanolic solution of tetramethylammonium hydroxide [21],... 

---