Tetrabutylammonium acetate

Tetrabutylammonium acetate, 20 h, 20°. For comparison, the 2,4-dichloro-phenyl group was removed in 100... 

Buffered tetrabutylammonium acetate (final pH 7.1) showed the best results, superior to the more popular phosphate salt, because of its high solubility in aqueous methanol and acetone and its fast reaction with chlorophylls to form hydrophobic... 

To obtain this compound the key step consisted in the epimerization of the C-5 in compound 6. This was acomplished by triflation of the alcohol 6 and nucleophilic substitution of the triflate by a large excess of tetrabutylammonium acetate in dichloromethane. A controlled (4 °C, 3 h) basic methanolysis of the enol benzoate led to the keto-ester 11" whose hydroxyl functions at C-4 and C-6 were simultaneously deprotected under acidic conditions to furnish 12. Finally a Zemplen deprotection of the 5-acetoxy group led to 13 obtained in five steps and 11% overall yield from 6 (figure 4). 

The original conditions used amines as solvents or cosolvents. Several other bases can replace the amine. Tetrabutylammonium hydroxide or fluoride can be used in THF (see Entry 1 in Scheme 8.11).163 Tetrabutylammonium acetate is also effective with aryl iodides and EWG-substituted aryl bromides (Entry 2).164 Use of alkenyl halides in this reaction has proven to be an effective method for the synthesis of enynes165 (see also Entries 5 and 6 in Scheme 8.11). 

A palladium catalyst with a less electron-rich ligand, 2,2-dipyridyl-methylamine-based palladium complexes (4.2), is effective for coupling of aryl iodides or bromides with terminal alkynes in the presence of pyrrolidine and tetrabutylammonium acetate (TBAB) at 100°C in water.37 However, the reactions were shown to be faster in NMP solvent than in water under the reaction conditions. Palladium-phosphinous acid (POPd) was also reported as an effective catalyst for the Sonogashira cross-coupling reaction of aryl alkynes with aryl iodides, bromides, or chlorides in water (Eq. 4.18).38... 

The selective reduction of the D-ring olefin in 106 using a partially poisoned catalyst (Pd/C, 0.25 % pyridine) provided intermediate 107 (83 %), which was epimerized at -78 °C with sodium methoxide (HOAc quench at -78 °C, 89 %) (Scheme 10.9). Deoxygenation by means of tosyl hydrazone 108 and subsequent treatment with catechol borane and tetrabutylammonium acetate gave pentacyclic... 

The addition of tetrabutylammonium acetate appeared to be very useful for desilylation of intermediates A (see Scheme 3.232). An efficient procedure was developed for the oxidation of nitroalkanes to nitroalkenes with the use of this reagent (250) (Scheme 3.234). 

Using the same initial step for the double serial inversion strategy, from methyl glucoside 37, the 2,4-tiiflate intermediates 50 could be produced via a Inflation process (Scheme 15). The 4-triflates of these intermediates were subsequently inversed to the corresponding 4-0-acetyl intermediates 51 by substitution with tetrabutylammonium acetate, followed by inversion of the 2-position by tetrabutylammonium nitrite, to yield a mixture of methyl... 

An alternative procedure is to convert the carbonyl compound into the toluene-p-sulphonylhydrazone,12 followed by reduction with either sodium borohydride in acetic acid,13 or with catecholborane, followed by decomposition of the intermediate with sodium acetate or tetrabutylammonium acetate.14 The former method is illustrated by the conversion of undecan-6-one into undecane (Expt 5.6), and the latter by the conversion of acetophenone into ethylbenzene (Expt 6.4, Method B). A feature of these methods is that with a, / -unsaturated ketones, migration of the carbon-carbon multiple bond occurs thus the tosylhydrazone of isophorone gives 3,3,5-trimethylcyclohex-l-ene, and the tosylhydrazone of oct-3-yn-2-one gives octa-2,3-diene. 

An alternative milder procedure is the reduction of the corresponding toluene-p-sulphonylhydrazones with catecholborane, followed by decomposition of the intermediate with sodium acetate in the presence of dimethyl sulphoxide, or with tetrabutylammonium acetate.1 These methods, which do not have the disadvantages of the Clemmensen reduction, are illustrated by the preparation of ethylbenzene from acetophenone (Expt 6.4, Methods A and B). Outline mechanisms for these reactions are given below. 

Method B. The toluene-p-sulphonylhydrazone of acetophenone (0.721 g, 2.5 mmol) (1), m.p. 140—141.5 °C, is placed in a flame-dried, nitrogen-filled flask containing 5 ml of chloroform. Catecholborane (0.52 ml, 5.0 mmol) (Section 4.2.7, p. 420) is added and the reduction allowed to proceed for 2 hours at room temperature (2). Methanol (1 ml) is added to destroy the excess of hydride followed by the addition of tetrabutylammonium acetate (0.7 g, 2.5 mmol). The reaction mixture is stirred for 4 hours when g.l.c. analysis indicates a 94 per cent yield of ethylbenzene. The product is isolated by distillation, yield 0.21 g (79%), b.p. 132-136 °C. 

Silyl enolates generated from a-allyloxy esters undergo the [2,3]-Wittig rearrangement on treatment with Lewis base such as tetrabutylammonium acetate or tetrabuty-lammonium 4-methoxybenzoate (Scheme 10).14... 

Palladium nanoparticles were further immobilised on chitosan flakes and from TEM it was established that they have a core-shell structure in which the metallic palladium is surrounded by a stabilising shell composed of a [(C4)4N]+ monolayer that is surrounded by Br and [PdCl4]2- species.1821 High catalytic activity for arylhalides including activated arylchlorides was observed at 130°C in [(C4)4N]Br using tetrabutylammonium acetate as base. 

Xylitol has been derived from the product of photo-oxidation of cyclopentadiene [204], (Z)-(4RS)-4,5-epoxypent-2-enal (Scheme 13.105). Chemoselective reduction of the formyl group gives cis-hydroxyepoxypentene 448, which is directly acetylated into 449. Treatment of 449 with tetrabutylammonium acetate in AC2O opens the epoxide with formation of 450. De-O-acetylation gives 451, the epoxidation of which with p-nitroperbenzoic acid generates a 3 7 mixture of epoxides 452 and 453, isolated as peracetates. The major epoxide 453 is hydrolyzed into xylitol via the orthoester 454. 

However, 1-acetoxy-1-phenylcyclopropanes can be synthesized by photolytic reaction of 3-acetoxy-3-phenyl-3//-diazirine (obtained from the corresponding bromo-diazirine and tetrabutylammonium acetate), with an alkcne. Excellent yields of acetoxycyclopropanes were obtained from alkenenitriles, e.g. 5, while a rather poor yield was obtained from 2-methylbut-2-... 

Figure 18.15 Optimization of gradient runtime and temperature [after J.W. Dolan etal., J. Chromatogr. A, 803,1 (1998)]. Conditions sample, algal pigments column, 25cm x 3.2 mm i.d. stationary phase, Vydac 201tp Ci8 5 j,m mobile phase, 0.65 ml min gradient from 70 to 100% methanol in 28 mM tetrabutylammonium acetate buffer pH 7.1. Top computer simulation of a separation at 57 C and 80 min gradient runtime middle computer simulation with three fused peak pairs at 55 °C and 54 min bottom experimental chromatogram underthese conditions.

The synthetic potential of these catalysts has been investigated in Heck-type coupling reactions treatment of l-bromo-4-nitrobenzene with n-butyl acrylate in isopropyl alcohol in the presence of 2.5 mol% of catalyst and tetrabutylammonium acetate afforded the unsaturated ester in an excellent... 

Catalytic asymmetric synthesis of the key intermediate 11 in the preparation of 3/1.8/ , 10a-trihydroxycapnellene and 3/ ,8/J,10a,14-telrahydroxycapnellene is achieved upon treatment of 5-methyl-5-(3-trifluoromethanesulfonyloxy-3-butenyl)-1.3-cyclopentadiene (10) with catalytic amounts of palladium(II) acetate, (S)-BINAP and tetrabutylammonium acetate in dimethyl sulfoxide. The (.STS..S (-enantiomer of 11 is obtained in 89% yield and 80% ce23,8 . In a similar cyclization reaction of the substrate which contains a vinyl iodide unit in the side chain, a much lower asymmetric induction w7as observed. 

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