Silyl group trimethyl

Monomers contained terminal phenylacetylenes protected with trimethyl-silyl groups and aryl iodides masked as N,hT-dialkyltriazenes. A typical PAM synthesis involved three basic transformations (Scheme 12) ... 

Alternative silylating reagents such as N,0-bis(trimethylsilyl)acetamide 22a (BSA) [39-43], N,0-bis(trimethylsilyl)trifluoracetamide 22b (BSTFA) [44], or N,N-bis(trimethylsilyl)formamide 22c (BSF) [41, 46], in which the N- and O-trimethyl-silyl groups are in equilibrium [45] (Scheme 2.4), are much more powerful silylating reagents [40, 45] but are more expensive than FIMDS 2, because they are usually prepared by heating formamides or acetamides with TCS 14/triethylamine... 

The ready exchange of silyl groups is apparent from the reaction of equimolecu-lar amounts of trimethylsilyl formate 148 with N-triethylsilyhnethylamine 163 for 1 h at room temperature (Scheme 4.4) whereupon two layers separate the upper layer consists of HMDSO 7 and l,l,l-trimethyl-3,3,3-triethyldisiloxane 64 and the lower layer contains N-methylformamide 164 in almost quantitative yield [5]. 

The 0-silylation reaction of alcohols is important as a protection method of hydroxyl groups. 0-Silylations of liquid or crystalline alcohols with liquid or crystalline silyl chlorides were found to be possible in the solid state. For example, when a mixture of powdered L-menthol (26), ferf-butyldimethylsilyl chloride (27), and imidazole (28) was kept at 60 °C for 5 h, 0-tert-butyldi-methylsilyl L-menthol (29) was obtained in 97% yield [8] (Scheme 4). Similar treatments of 26 with the liquid silyl chlorides, trimethyl- (30a) and triethylsilyl chloride (30b), gave the corresponding 0-silylation products 31a (89%) and 31b (89%), respectively, in the yields indicated [8] (Scheme 4). However, 0-silylation of triisopropyl- (30c) and triphenylsilyl chloride (30d) proceeded with difficultly even at 120 °C and gave 31c (57%) and 31d (70%), respectively, in relatively low yields. Nevertheless, when the solvent-free silylation reactions at 120 °C were carried out using two equivalents of 30c and 30d, 31c (77%) and 31d (99%) were obtained, respectively, in relatively high yields. 

As with aldol and Mukaiyama addition reactions, the Mannich reaction is subject to enantioselective catalysis.192 A catalyst consisting of Ag+ and the chiral imino aryl phosphine 22 achieves high levels of enantioselectivity with a range of N-(2-methoxyphenyljimines.193 The 2-methoxyphenyl group is evidently involved in an interaction with the catalyst and enhances enantioselectivity relative to other A-aryl substituents. The isopropanol serves as a proton source and as the ultimate acceptor of the trimethyl silyl group. 

The chemical shifts of jp3-hybridized silicon atoms, such as a trimethyl-silyl group attached to the jp2-hybridized silicon in silenes, are normally found from -10 to -18 ppm, as compared to the position at -9.8 ppm for the trimethylsilyl groups of (Me3Si)4Si (the central silicon atom of this compound resonates at -135.5 ppm). On the other hand, a trimethylsiloxy group attached to carbon, either sp2- or sp3-hybridized, normally absorbs in the range from +5 to +20 ppm. 

The observed /runfavorable interaction between the trimethyl-silyl group and the allenyl group (Scheme 72). 

Some interesting reactions have recently been found to occur on heating cycloheptatriene with some organosiliconruthenium carbonyls. An unexpected feature of these reactions is the migration of trimethyl-silyl groups from the metal to the 7r-ligand (R = Me) (17, 74) ... 

In the reduction of conjugated dienes cis 1,4-addition of trimethyl-chlorosilane to give c -l,4-bis(trimethylsilyl)-2-butene is favored with sodium in THF, lithium naphthalide in THF, and with lithium in diethylether. It appears that the anion radical, which in nonionizing solvents should exist in a cis configuration, leads to the cis 1,4-addition of the silyl groups, whereas the dianions produced by further reduction lead to trans products (140). 

Hydrostannation of (l-alkynyl)carbene chromium complexes involves addition to the M = C bond as well as to the C=C bond and is strongly influenced by the substituent at the alkynyl moiety. By the bulky trimethyl-silyl group of compound lg, a 1,1-addition to the carbene carbon atom is promoted with formation of a densely functionalized 1,3-heterobimetal lie propargyl reagent 93 containing both a stannyl and a silyl group. A 3,1-addition is observed with phenyl derivative la and also the vinyl compound lo, which leads to production of an allene 94 and 95, respectively (Scheme 31).111... 

Eq. 1) [5]. On the other hand, Kikukawa and his co-workers found that the reaction of trimethyl(a- or -styryl)silane with arenediazonium tetrafluoroborates gave regioisomeric mixtures of coupling products [6-8]. The catalytic cycle of the reaction is considered to involve carbopalladation toward the C-C double bond of an alkenylsilane by an arylpalladium intermediate followed by tetraflu-oroborate-assisted elimination of the silyl group and regeneration of a palladi-um(0) species (Scheme 1). 

The comparison of propene, allyltrimethylsilane, and isobutene indicates, that introduction of a trimethyl silyl group in /3-position of the developing carbenium center activates more than a methyl group in a-position. Both series of triphenyl element compounds (left and right column Scheme 44) show the reactivity pattern Si < Ge < Sn, but variation of the substituents at silicon and tin was found to largely affect the reactivity of the double bond. While in the allyl series (right column), the trialkylsilanes and -stannanes are 2 to 3 orders of magnitude more reactive than the... 

Next, it is interesting to look at the results in the fourth column of the table. Here, the theoretical C Is/Si 2p ratio should be 3, the stoichiometry of the labelling trimethyl silyl group. The values found for Y58 substrates are 3.2 and 2.9, while larger values between 3-5 were observed for the oxide substrates. The latter large... 

Allenediynes are obtained from the coupling of allenic bromides with terminal diynes . Thus from the bromide 53 and butadiynyl(trimethyl)silane (13) in the presence of copper(i) bromide and tri-/i-butylamine, the silylated derivative 54 was obtained in 70% yield. Removal of the silyl group by treatment with dilute methanolic alkali for 10 s afforded the free allenediyne 55 in 84% yield. 

The formation of compound 109 can be explained in terms of oxidative addition of an sp-hybridized C-Si bond of the coordinated bis(trimethylsilyl)acetylene, in complex 113, to the nickel atom, followed by a shift of the trimethyl-silyl group from the nickel atom to the trimethylsilyl-substituted sp carbon, giving vinylidenenickel complex 114 (Scheme 14). 

The catalyst (PPh3)3RuCl in the presence of DPPB is an efficient reagent for the hydrophosphorylation of olefins. The reaction is highly sensitive to olefin substitution and monosubstituted olefins can be reliably converted to their aliphatic phosphonates in the presence of other olefins. Additionally, a trimethyl-silyl group is an effective acetylene protecting functionality that reverses the normal preference for alkyne hydrophosphorylation over a terminal olefin (Scheme 54). 

Few organoytterbium(II) alkyls have been synthesized [15,16]. The trimethyl-silyl group features prominently in ligands such as the bis(trimethylsilyl)methyl and tris(trimethylsilyl)methyl. These compounds, whose reactivity is currently... 

The TriMethyl Silyl group is sometimes abbreviated to TMS. As this is not much shorterthan MesSi, we shall use the real thing instead of the abbreviation. 

Butyllithium removes a proton from each Cp group, and the dilithio derivative then reacts with trimethylchlorosilane to give the disilylstannocene, and this process can be repeated to put three silyl groups in each ring.1" Trimethyl(diethylamino)tin similarly acts as a strong base, and gives the distannylated stannocene.118... 

This sensitivity toward lateral attacks explains the four times shorter duration of action of sila-meprobamate compared to its carbon isostere on a model of tranquiUizing activity in mice (rotarod test, potentiation of hexobarbital-induced sleep, and intraperitoneal injection). " On the other hand, when given orally, sila-meprobamate is practically inactive. One of the first metabolites formed has been characterized as being a di-siloxane (Figure 15.67). For the two phenyl-trimethylsilyl-derived AChE inhibitors, the rather positively charged trimethyl-silyl group mimics the trimethyl-ammonium function present in acetylcholine. Eor these compound metabolic oxidation does not take place on the silicon, but on one of methyl groups (S1-CH3 Si—CH2—OH). ... 

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