Butylammonium formate

The allyl group played a key role in a synthesis of a phosphorylated and glycosylated peptide fragment of mammalian RNS polymerase II.48 The allyl group was selected for the protection of both the phosphate and amino group of the terminal serine of the hexapeptide 26 1 [Scheme 7.26], because its reductive cleavage with butylammonium formate and Pd(0) could be accomplished without elimination of the phosphate or N-acetylglucosamine units attached to the three serine residues. 

Corey and Terashima used the Sn2 displacement with tetra-n-butylammonium formate in one step in a synthesis of ent-l l.lS-epi-POF.j (6). Thus reaction of (4) with 6.7 eq. of tetra-n-butylammonium formate in acetone at 25° for 16 hr. gave the inverted formate (5), which was transformed, by a sequence used previously, into (6). 

In contrast, reaction of (1) with tetra- -butylammonium formate (see also Tetraethylammonium formate, 1, 1137-1138) under the same conditions gave the inverted formate (2b) and the cyclopentene (3) in a ratio of 3 1. The greater tendency for substitution at carbon by formate ion relative to acetate ion may be owing to smaller size or to decreased basicity. 

Compton R G, Spaokman R A, Wellington R G, Green M L H and Turner J 1992 A Cgg modified eleotrode. Eleotroehemioal formation of tetra-butylammonium salts of Cgg anions J. Electroanal. Chem. Interfacial... 

In addition, NaOMe, and NaNH2, have also been employed. Applieation of phase-transfer conditions with tetra-n-butylammonium iodide showed marked improvement for the epoxide formation. Furthermore, many complex substituted sulfur ylides have been synthesized and utilized. For instance, stabilized ylide 20 was prepared and treated with a-D-a/lo-pyranoside 19 to furnish a-D-cyclopropanyl-pyranoside 21. Other examples of substituted sulfur ylides include 22-25, among which aminosulfoxonium ylide 25, sometimes known as Johnson s ylide, belongs to another category. The aminosulfoxonium ylides possess the configurational stability and thermal stability not enjoyed by the sulfonium and sulfoxonium ylides, thereby are more suitable for asymmetric synthesis. 

Penton and Zollinger (1979, 1981 b) reported that this could indeed be the case. The coupling reactions of 3-methylaniline and A,7V-dimethylaniline with 4-methoxy-benzenediazonium tetrafluoroborate in dry acetonitrile showed a number of unusual characteristics, in particular an increase in the kinetic deuterium isotope effect with temperature. C-coupling occurs predominantly (>86% for 3-methylaniline), but on addition of tert-butylammonium chloride the rate became much faster, and triazenes were predominantly formed (with loss of a methyl group in the case of A V-di-methylaniline). Therefore, the initial attack of the diazonium ion is probably at the amine N-atom, and aminoazo formation occurs via rearrangement. 

The ammonium catalyst can also influence the reaction path and higher yields of the desired product may result, as the side reactions are eliminated. In some cases, the structure of the quaternary ammonium cation may control the product ratio with potentially tautomeric systems as, for example, with the alkylation of 2-naph-thol under basic conditions. The use of tetramethylammonium bromide leads to predominant C-alkylation at the 1-position, as a result of the strong ion-pair binding of the hard quaternary ammonium cation with the hard oxy anion, whereas with the more bulky tetra-n-butylammonium bromide O-alkylation occurs, as the binding between the cation and the oxygen centre is weaker [11], Similar effects have been observed in the alkylation of methylene ketones [e.g. 12, 13]. The stereochemistry of the Darzen s reaction and of the base-initiated formation of cyclopropanes under two-phase conditions is influenced by the presence or absence of quaternary ammonium salts [e.g. 14], whereas chiral quaternary ammonium salts are capable of influencing the enantioselectivity of several nucleophilic reactions (Chapter 12). 

Tetrabromopyridine reacts with 1,2-dihydroxybenzcne to yield the dibromoazaphenoxane [34], Tetra-n-butylammonium fluoride catalyses the conversion of 5-chloro-l-phenyltetrazole into tetrazol-5-yl glycosides, which are useful precursors for the formation of glycosyl fluorides [45]. 

As the integrity of chiral alcohols are retained in the phase-transfer catalysed O-alkylation, the procedure is valuable for the synthesis of chiral ethers under mild conditions as, for example, in the preparation of alkoxyallenes via the initial formation of chiral propargyl ethers [8]. It has been proposed that a combination of 18-crown-6 and tetra-n-butylammonium iodide provide the best conditions for the O-benzylation of diethyl tartrate with 99% retention of optical purity [9]. 

The almost instantaneous intramolecular ether formation by reaction of phenoxy anions, generated from the silyl ethers with a stoichiometric amount of tetra-n-butylammonium fluoride, on mesylate esters has been used to synthesize labile benzo-0-2-isocephams (>90%) [20]. 

The direct formation of A-substituted phthalimides from phthalic anhydride and alkyl azides, via the intermediate RN=PPh, compound, is catalysed by the presence of tetra-n-butylammonium cyanide [34],... 

A phase-transfer catalysed nucleophilic displacement reaction on chloro-acetanilides by cyanate ions, followed by ring-closure (Scheme 5.10), provides a simple and viable synthesis of hydantoins [41], The formation of the hydantoins is inhibited by substituents in the orf/to-position of the aryl ring, but the addition of potassium iodide, or tetra-n-butylammonium iodide, generally increases the overall rate of formation of the cyclic compounds, presumably by facilitating the initial nucleophilic substitution step. 

Zirconium tetrachloride promotes a tandem nucleophilic addition and aldol-type condensation reaction of methyl propynoate, or /V,/V-dimethylpropynamidc, with aldehydes, or ketones, in the presence of tetra-n-butylammonium iodide (Scheme 6.13) [8] with a high selectivity towards the formation of Z-isomers. A similar reaction occurs between aliphatic and aromatic aldehydes and penta-3,4-dien-2-one to yield 1-substituted 2-acetyl-3-iodobut-3-enols (50-75%) [9]. 

Carbanions, generated by the reaction of benzylsilanes with tetra-n-butylammo-nium fluoride react with non-enolizable aldehydes to produce the alcohol [67], When a stoichiometric amount of the ammonium fluoride is used, the methylarene corresponding to the benzylsilane is frequently a by-product and arises from formation of the hydrogen difluoride salt during the reaction. When only catalytic amounts of the ammonium fluoride initiate the reaction, the formation of the methylarene is suppressed. In a similar type of reaction (although the mechanism is not known) between aldehydes and ketones, allyl bromide, and tin in the presence of trimethylsilyl chloride the yield of the but-l-en-4-ol is raised significantly by the addition of tetra-n-butylammonium bromide, particularly in the reactions with... 

Palladium-catalysed C-C bond formation under Heck reaction conditions, which normally requires anhydrous conditions and the presence of copper(I) salts, is aided by the addition of quaternary ammonium salts. It has been shown that it is frequently possible to dispense with the copper catalyst and use standard two-phase reactions conditions [e.g. 18, 19]. Tetra-/i-butylammonium salts catalyse the palladium-catalysed reaction of iodoarenes with alkynes to yield the arylethynes in high yield [20, 21], whereas the reaction with 3-methylbut-1 -yn-3-ol (Scheme 6.30) provides a route to diarylethynes [22]. Diarylethynes are also formed from the reaction of an iodoarene with trimethylsilylethyne [23], Iodoalkynes react with a,p-unsaturated ketones and esters to produce the conjugated yne-eneones [19],... 

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