Arylation Tris sulfonium difluorotrimethylsilicate

Fluoride ion catalyzes the hydrosilylation of both alkyl and aryl aldehydes to silyl ethers that can be easily hydrolyzed to the free alcohols by treatment with 1 M hydrogen chloride in methanol.320 The most effective sources of fluoride are TBAF and tris(diethylamino)sulfonium difluorotrimethylsilicate (TASF). Somewhat less effective are CsF and KF. Solvent effects are marked. The reactions are facilitated in polar, aprotic solvents such as hexamethylphosphortriamide (HMPA) or 1,3-dimethyl-3,4,5,6-tetrahydro-2(l //)-pyrirnidinone (DMPU), go moderately well in dimethylformamide, but do not proceed well in either tetrahydrofuran or dichloromethane. The solvent effects are dramatically illustrated in the reaction of undecanal and dimethylphenylsilane to produce undecyloxyphenyldimethylsi-lane. After one hour at room temperature with TBAF as the source of fluoride and a 10 mol% excess of silane, yields of 91% in HMPA, 89% in DMPU, 56% in dimethylformamide, 9% in tetrahydrofuran, and only 1% in dichloromethane are obtained (Eq. 164).320... 

Unactivated aryl iodides undergo the conversion Arl — ArCHj when treated with tris(diethylamino)sulfonium difluorotrimethylsilicate and a palladium catalyst.131 A number of methods, all catalyzed by palladium complexes, have been used to prepare unsymmetrical biaryls (see also 3-16). In these methods, aryl bromides or iodides are coupled with aryl Grignard reagents,152 with arylboronic acids ArB(OH)2,153 with aryltin compounds Ar-SnR3,154 and with arylmercury compounds.155 Unsymmetrical binaphthyls were synthesized by photochemically stimulated reaction of naphthyl iodides with naphthoxide ions in an SrnI reaction.156 Grignard reagents also couple with aryl halides without a palladium catalyst, by the benzyne mechanism.157 OS VI, 916 65, 108 66, 67. 

ArOCH(Rl)OR2 —> ArOH.1 Alkoxymethyl aryl ethers are cleaved by P2I4 in CH2C12 at 25° to phenols in 55-90% yield. This reagent is more useful for cleavage of SEM, MOM, and MEM ethers than Bu4NF, BBr3, or tris(diethylamino)sulfonium difluorotrimethylsilicate (TASF). 

It is a palladium-catalyzed cross-coupling reaction between organosilanes (vinyl, ethynyl and allylsilanes) and organic halides (aryl, vinyl and allyl halides). Allylpal-ladium chloride dimmer [( ri -C3H5PdCl)2] and either tris(diethylamino)sulfonium difluorotrimethylsilicate (TASF) or tetra-n-butylammonium fluoride (TBAF) are used as catalysts. Fluoride ion acts as an activator for the coupling, forming an intermediate hypervalent anionic silicon species, which can then transmetallate with palladium as a preliminary reaction to coupling. 

Trimethyl(trifluoromethyl)silanc is easily fluorodesilylated by tris(dimethylamino)sulfonium difluorotrimethylsilicate [TASF(Me)], tetrabutylammonium fluoride, or tris(diethylamino) (methylamino)phosphonium hydrogen difluoride and, if arenesulfonyl fluorides are used to trap the trifluoromethyl anion, trifluoromethyl sulfones arc formed in high yield. Trisfdiethyl-amino)(methylamino)phosphonium phenolate is also an effective catalyst for this reaction, but TASF(Me) is favored as it can achieve the quantitative transformation of ArS02F into aryl trifluoromethyl sulfones.115-117... 

Similar conditions have been applied to 2-methy -3-oxoamides, except that tris(diethyl-amino)sulfonium difluorotrimethylsilicate (TASF) was used as the fluoride source and 1,3-dimethyl-3,4,5.6-tetrahydro-2(l//)-pyrimidinone (DMPU) as solvent3,4. Again the results were generally complementary to those given by the silane/trifluoroacetic acid system, in that the ewfi-product w as formed predominantly. However, the method only worked reliably for amides where R1 is aryl. The ester (5)-methyl 2-benzoylpropanoate failed to react, possibly because of deprotonation by fluoride4. 

Palladium-Catalyzed Coupling Reaction with Organo-halides. In the presence of tetrakis(triphenylphosphine)-palladium(O), vinyl halides (12) are converted to the corresponding vinylsilanes (13) with the aid of MegSi2 and tris-(dimethylamino)sulfonium difluorotrimethylsilicate (TASF) in 53-92% yields with high chemoselectivity and stereospecificity (eq 6). Similarly, aryl-, benzyl-, and allylsilanes are obtained from the corresponding halides in 57-100, 8 8, and 52-93% yield, respectively. Allyl esters also are transformed by Pd-catalyzed reaction of Me6Si2 into allylsilanes. ... 

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