Tetrabutylammonium fluoride/DMSO

Advances of the past three decades, however, have produced alternatives to the heavy metal-based cellulose solvents. Prominent among them are dimethylacetamide/LiCl (DMAc/LiCl) N,MMN-0 hydrate (NMMO) tetrabutylammonium fluoride/DMSO (TBAF/DMSO) and potassium thiocyanate/DMSO [48]. While many of these solvents have gained significant popularity among laboratory chemists, only the amine oxide solvent, N,MMNO, has achieved industrial practicality. This will be discussed in the section on regenerated cellulose fibers. Several other important physical properties of cellulose are given in O Table 4. 

For the removal of this protecting group, tetrabutylammonium fluoride in oxolane is the most frequently used [388, 389, 409-411]. A much simpler reagent to prepare, potassium fluoride — crown ether, has been introduced for the same purpose [427]. Silyl group at 0-2 of nucleosides is cleaved more rapidly [411] than at 0-5. Acyl migrations occurred under the tetrabutylammonium fluoride-catalyzed desilyla-tion [432, 434, 443], Differencies between the primary and secondary position were also observed for acid- or base-catalyzed solvolysis [391, 409-412], 5 -0-(7ert-butyl-dimethylsilyl)nucleosides are much more labile towards acid than either 2 - or 3 -silyl ethers [391, 410-412], whereas the situation is reversed for base hydrolysis [411], /V-Bromosuccinimide in aqueous DMSO is another alternative for the removal of this type of silyl group [444]. 

Both experimental and theoretical studies have been reported of fluoro-denitration and fluoro-dechlorination reactions using anhydrous tetrabutylammonium fluoride in DMSO. The absences of ion pairing and strong solvation are critical in contributing to the reactivity of the fluorinating agent24 Quaternary ammonium salts derived from cinchona alkaloids have been shown to be effective catalysts in an improved asymmetric substitution reaction of /1-dicarbonyl compounds with activated fluoroarenes. The products may be functionalized to yield spiro-oxindoles.25... 

Scheme 12.6. Catalytic asymmetric synthesis of PC Ei using a Noyori-type 3CR, by Feringa and co-workers [19]. TBAF = n-tetrabutylammonium fluoride, THF = tetrahydrofuran, DMSO = dimethylsulfoxide, Ac = acetyl, DMAP = 4-dimethylaminopyridine, pyr = pyridine.

Heinze et al. found that DMSO in combination with tetrabutylammonium fluoride trihydrate dissolved cellulose (degree of polymerization < 650) within 15 min at room temperature [38]. They also demonstrated that homogeneous esterification of cellulose is possible in this solvent system. The applicability of this new solvent system to cellulose grafting has recently been proved by adoption of cyclic compounds such as lactones and N-carboxy a-amino acid anhydrides (NCAs) [39]. e-Caprolactone was facilely graft-polymerized on cellulose at a graft rate of 65% (per trunk weight of 100), and NCAs at over 100%, in the respective homogeneous reaction systems at < 60 °C. 

Numerous dioxetanes with varying atom (X) and protecting group (PG) have been synthesized over the last decade in order to study the CIEEL mechanism. The following serve as prototypical examples. The most prevalent trigger is that of a siloxyphenyl substituent such as that incorporated into dioxetane 54. Tetrabutylammonium fluoride (TBAF) is used in an aprotic solvent, such as dimethyl sulfoxide (DMSO) or acetonitrile, to desilylate to afford the unstable phenolate 55 (Scheme 11) <2002MI305>. 

Chemicals AIBN CAN DIBAL DMAP DMSO HMPA LAH LDA mCPBA NBS NCS or PCC PDC Py TBAF TEMPO a.a -azobislisobutyronitrile) cerium(IV) ammonium nitrate diisobutylaluminium hydride 4-(dimethylamino)pyridine dimethyl sulfoxide hexamethylphosphoramide lithium aluminum hydride lithium diisopropylamide m-chloroperoxybenzoic acid A-bromosuccinimide A-chlorosuccinimide superoxide anion radical pyridinium chlorochromate pyridinium dichromate pyridine tetrabutylammonium fluoride 2,2,6,6-tetramethyl-l-piperidinyloxy free radical... 

The best results have been obtained in the non-polar solvents heptane or 0-xylene. Polar aprotic solvents such as Me2CO, MeCN, DMSO or dioxane gave poor yields and byproduct formations. Water-free conditions to avoid hydrolysis of BC14- have been necessary. The best fluorination yields have been achieved in the 373-393 K temperature interval (in 0-xylene with TBAF, tetrabutylammonium fluoride). An increase in the yield was observed if an excess of the diazonium salt was used. The total labelling procedure took 50 min. The tetrachloroborate incorporates fluoride by a halide exchange reaction (equation 3)9 10. 

First, we examined BID of 1. When 1 was treated with tetrabutylammonium fluoride (TBAF) in A-methylpyrrolidone (NMP) at 45 °C, chemiluminescence occurred effectively with An,axBI = 498 nm, (P610 = 0.29, and rate constant BID = ln2/ti/2BID = 2.5 x 10 4 s 1 (vide infra). The BID of 1 also proceeded to give bright light in acetonitrile,3 DMF and DMSO. The chemiluminescence spectra for BID of 1 are... 

Homocoupling of aryl iodides to form biaryls with this complex in the presence of tetrabutylammonium fluoride has been carried out in DMSO at 120°. ... 

If you examine Table 1.1, you are likely to arrive at the conclusion that fluoride is not a particularly good nucleophile. Recently, Stephen DiMagno and coworkers at the University of Nebraska synthesized anhydrous tetrabutylammonium fluoride (TBAFaj j) via the following reaction, and found it to be a highly active form of nucleophilic fluoride in dry DMSO and other polar aprotic solvents (Sun, H. Dimagno, S. J. Am. Chem. Soc. 2005,127, 2050-2051) ... 

DMSO/TBAF Dimethyl sulfoxide/ tetrabutylammonium fluoride... 

The initial olefination was accomplished using the Wittig olefination conditions developed by Corey (NaH/DMSO) to afford E/Z mixtures of enol ethers. The enol ethers undergo hydrolysis to the corresponding aldehydes upon treatment with 5% aqueous HF in acetonitrile. Modest degrees of stereoselectivity were observed. The ability of fluoride to mediate the hydrolysis of the (trimethylsilyl)ethoxymethyl moiety may provide opportunities not available when (methoxymethyl)triphenylphosphonium salts are employed. However, it should be noted that Zbiral and Schonauer reported that hydrolysis could not be realized with the use of tetrabutylammonium formate or triethylamine 2HF. 

The binding behavior of these receptors at 25 °C was investigated first by proton NMR spectroscopy in CD3CN/DMSO-t/e (9 1 v/v), as well as by UV-vis spectroscopy and isothermal titration calorimetry in MeCN/DMSO (97 3, v/v). The receptors displayed a selective colorimetric response when exposed to the fluoride, dihydrogen phosphate, and acetate anions (studied in the form of the corresponding tetrabutylammonium salts) and an enhanced affinity as compared to a comparable calix[4]pyrrole system lacking the dipyrrolylquinoxaline-containing strap. 

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