Silyl arenes

A second synthetic procedure for preparing silylated arene complexes, based on the metalation of a preformed rj6-arene complex, followed by treatment with an organochlorosilane, has been used only in one case so far namely, bis(benzene)chromium (47) ... 

Desilylfunctionalizations. Aryltrichlorostannanes are formetf when activated silyl arenes (o- orp-methoxylated) are heated with SnCl,. Catalyzed reactions of allylsilanes with tris(phenylchalcogeno)methanes give homologous chalcogenacetals. ... 

Several examples of -butyllithium/potassium terf-butoxide promoted metalations of benzenes, naphthalenes, tert-alkyl-substituted benzenes, phenyl acetylenes, and silylated arenes can be found in Table 4. 

The reaction of Ba[P(SiMe3)2]2(THF)2 with diphenylbutadiyne in toluene for 12 days induces a m-addition of the diyne to the phosphide, followed by a 1,3-silyl group shift and ring closure. The dinuclear complex 132 is then isolated in good yield.283 Its complex structure contains Ba-C a bonds (2.881(5), 2.899(5) A), side-on Ba-alkyne (3.003(6), 3.363(6) A) and arene interactions, and Ba-phospholide bonds (Ba-P = 3.487(2) A) (Figure 65). 

The iridium complex composed of l/2[ Ir(OMe)(cod)2 ] and 4,4 -di-/ r/-butyl-2,2 -bipyridine (dtbpy) shows a high catalytic activity for aromatic G-H silylation of arenes by l,2-di-/z r/-butyl-l,l,2,2,-tetrafluorodisilane.142 The reaction of 1,2-dimethylbenzene with l,2-di-/< r/-butyl-l,l,2,2,-tetrafluorodisilane in the presence of l/2[ Ir(OMe)(cod)2 ] and dtbpy gives 4-silyl-l,2-dimethylbenzene in 99% yield (Equation (103)), which can be utilized for other functionalizations such as arylation and alkylation. 

The use of reactive metal electrodes are also effective for the silylation of various organic halides and simple arenes [75]. For instance, Dunogues et al. reported that electrolysis of aryl chlorides in the presence of excess Me3SiCl in a one-compartment cell equipped with a sacrificial aluminum anode in 80 20 THF/HMPA gave the corresponding aryltrimethylsilanes (Scheme 36). When... 

Oxidation of silyl enol ethers. Oxidation of silyl enol ethers to a-hydroxy aldehydes or ketones is usually effected with w-chloroperbenzoic acid (6, 112). This oxidation can also be effected by epoxidation with 2-(phenylsulfonyl)-3-( p-nitrophenyl) oxaziridine in CHC1, at 25-60° followed by rearrangement to a-silyloxy carbonyl compounds, which are hydrolyzed to the a-hydroxy carbonyl compound (BujNF or H,0 + ). Yields are moderate to high. Oxidation with a chiral 2-arene-sulfonyloxaziridine shows only modest enantioselectivity. 

Different nucleophiles such as methanol, allylsilanes, silyl enol ethers, trimethylsilyl-cyanide, and arenes can be used in this process [62]. When the sulfide itself contains an unsaturated or aromatic fragment and the process is carried out in the absence of a nucleophile, an intramolecular anodic sub-stitution/cyclization might occur [61-63]. Methyl esters of 2-benzothiazolyl-2-alkyl or aryl-acetic acid, oxidized in MeOH/Et4 NCIO4 or H2SO4 in the presence of CUCI2, form 2,2-dimethoxy products (Eq. 7) [64]. 

The Dotz benzannulation reaction yields either arene chromium tricarbonyl complexes or the decomplexed phenols, depending on the work-up conditions. Because of the instability of hydroxy-substituted arene chromium tricarbonyl complexes, yields of the latter tend to be low. High yields of arene complexes can, however, be obtained by in situ silylation of the crude product of the benzannulation reaction [336]. Oxidative work-up yields either decomplexed phenols or the corresponding quinones. Treatment of the benzannulation products with phosphines also leads to decomplexed phenols [272]. 

A wide range of olefins can be cyclopropanated with acceptor-substituted carbene complexes. These include acyclic or cyclic alkenes, styrenes [1015], 1,3-dienes [1002], vinyl iodides [1347,1348], arenes [1349], fullerenes [1350], heteroare-nes, enol ethers or esters [1351-1354], ketene acetals, and A-alkoxycarbonyl-[1355,1356] or A-silyl enamines [1357], Electron-rich alkenes are usually cyclopropanated faster than electron-poor alkenes [626,1015],... 

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