Tetrabutylammonium aryl

Aryl and alkylxanthates are converted into difluoro(methylthw)methyl ethers with tetrabutylammonium dihydrogen trifluoride and Af-bromosuccinimide in... 

The palladium-catalyzed cross-coupling of alkenylsilanols has been extensively studied with respect to the structure of both the silicon component and the acceptor halide. The preferred catalyst for coupling of aryl iodides is Pd(dba)2 and for aryl bromides it is [allylPdCl]2. The most effective promoter is tetrabutylammonium fluoride used as a 1.0M solution in THF. In general the coupling reactions occur under mild conditions (room temperature, in 10 min to 12 hr) and some are even exothermic. 

These reactions are convenient methods for putting sulfur-containing groups onto an aromatic ring. With Ar S", diazosulfides Ar—N=N—S—Ar are intermediates, which can in some cases be isolated. Thiophenols can be made as shown above, but more often the diazonium ion is treated with EtO—CSS" or S2", which give the expected products, and these are easily convertible to thiophenols. Aryl triflates have been converted to the aryl thiol using NaST(P5) and a palladium catalyst, followed by treatment with tetrabutylammonium fluoride. See also 14-27. 

Water insoluble tetrabutylammonium metaperiodate, which can be prepared from sodium metaperiodate and tetrabutylammonium hydrogen sulphate in aqueous solution, was found to be a useful reagent for the selective oxidation of sulphides in organic solvents . The reaction was generally carried out in boiling chloroform and gave dialkyl, alkyl aryl and diaryl sulphoxides in yields which are comparable with those reported for sodium metaperiodate in aqueous methanol solution (Table 4). In the case of diaryl sulphoxides, the yields decrease with prolonged reaction time. 

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 10-57-5-hydridosiliconate ion 62 is known in association with lithium,323 tetrabutylammonium,101 and bis(phosphoranyl)iminium93 cations. It is synthesized by hydride addition to the 8-.S7-4-silane 63, which is derived from hexafluoroacetone.101 Benzaldehyde and related aryl aldehydes are reduced by solutions of 62 in dichloromethane at room temperature101 or in tetrahydrofuran at 0°96 within two hours. The alkyl aldehyde, 1-nonanal, is also reduced by 62 in tetrahydrofuran at O0.96 Good to excellent yields of the respective alcohols are obtained following hydrolytic workup. The reactions are not accelerated by addition of excess lithium chloride,96 but neutral 63 catalyzes the reaction, apparently through complexation of its silicon center with the carbonyl oxygen prior to delivery of hydride from 62.101... 

A simple procedure for the synthesis of 4,5-disubstituted 1,2,3-triazoles 1247 involves stirring a mixture of nitroethene 1245 with trimethylsilyl azide and tetrabutylammonium fluoride at 30 °C for 3h. No solvent is needed. Triazoline 1246, which forms in the first step of the reaction, eliminates nitrous acid, and the trimethylsilyl group is cleaved off by the fluoride anion to afford triazole 1247. Various aryl and heteroaryl substituents R are used providing triazoles 1247 in 70-90% yield (Scheme 207) <2005JOC6526>. 

The arylation of heteroaromatic compounds is also achieved by aryl-aryl coupling reaction. The arylation of A-methylimidazole with bromobenzene occurs under palladium catalysis (Equation (62)).72 The arylation of thiazole with aryl iodide occurs at the 2-position under PdCl2(PPh3)2/CuI catalysis.73 In this case, tetrabutylammonium fluoride improves the activity of the catalyst. Alternatively, thiazoles and benzothiazole are efficiently arylated... 

The aryl bromide 40, prepared from cross-coupling between 1,2-dibromobenzene and (trimethylsilyl)acetylene, was converted to the corresponding arylzinc halide 41a and arylboronic acid 41b for subsequent coupling with the haloallenes 42 to produce the benzannulated enyne-allene 43 in -40% yield (Scheme 20.10) [38]. Desilylation with tetrabutylammonium fluoride (TBAF) then afforded 44 in 67% yield. 

Although aryl bromides and iodides reacted well without any additive (Scheme 32), tetrabutylammonium bromide (TBAB) was effective at improving the reactivity of aryl triflates under these conditions (Scheme 33). 

Cycloaddition of benzyne intermediates with aminothiazadienes provide access to substituted 2,4-diamino-4//-l,3-benzothiazines 196 in high yields. The benzynes are prepared by the treatment of (phenyl)[o-(trimethylsilyl)aryl]-iodonium triflates with 1.5 equiv of tetrabutylammonium fluoride (Scheme 20). Interestingly, 3-substituted-l,2-benzisothiazoles 197 are obtained when 4 equiv of tetrabutylammonium fluoride is used <2005H(65)1615>. 

Carbonylative cross-coupling of iodoarenes and aryl triflates with g< ///-fluorovinyltributylstannane takes place smoothly in a standard system, with triflate substrates requiring the addition of tetrabutylammonium iodide (Equation (4)). ... 

The use of the heteroaryl Heck reactions extends beyond fine chemicals synthesis. Polythiophenes were prepared starting from 3-octyl-2-iodotiophene by heating in the presence of palladium acetate and tetrabutylammonium chloride (6.91.),122 The arylation of benzothiophene has also been achieved under the same conditions.123... 

The palladium catalyzed cross-coupling of organosilicon compounds and aryl halides found only limited application with azines compared to the Suzuki or Negishi coupling. In a recent paper DeShong reported the efficient coupling of bromopyridine derivatives with aryl siloxanes (7.44.) 62 The transmetalating ability of the siloxane was enhanced by the addition of tetrabutylammonium fluoride. 

This method can be applied to introduce CF, and CF3 groups at oxygen and nitrogen atoms in various molecules. oe,a-Difluoro ethers are prepared from O-alkyl(aryl) carbothioales in moderate to good yields by reaction with tetrabutylammonium dihydrogen trifluoride and /V-bromosuccinimide or /V-iodosuccinimide,64 or with bromine trifluoride.65... 

Although true for many oximes of aliphatic and alicyclic ketones, the previous sequence is not absolute and can change depending on the reaction conditions and ketoxime type. Tetrabutylammonium hydroxide, for instance, which catalyzes fairly actively in the synthesis of 4,5,6,7-tetrahydroindole from cyclohexanon oxime and acetylene (79KGS197), turned out to be nearly inert with alkyl aryl ketoximes (78ZOR1733). 

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