Silyl substitution

The lithium enolate of the oc-silyl-substituted iron-acyl complex 19 reacts with aldehydes, however, products of the Peterson elimination process (E)- and (Z)-22 are usually isolat-ed22- 23,36.37 for t[1js anc other preparations of a,/t-unsaturated iron-acyl complexes see Section I.3.4.2.5.I.3.). 

Structural analogues of the /]4-vinylketene E were isolated by Wulff, Rudler and Moser [15]. The enaminoketene complex 11 was obtained from an intramolecular reaction of the chromium pentacarbonyl carbene complex 10. The silyl vinylketene 13 was isolated from the reaction of the methoxy(phenyl)-carbene chromium complex 1 and a silyl-substituted phenylacetylene 12, and -in contrast to alkene carbene complex 7 - gave the benzannulation product 14 after heating to 165 °C in acetonitrile (Scheme 6). The last step of the benzannulation reaction is the tautomerisation of the /]4-cyclohexadienone F to afford the phenol product G. The existence of such an intermediate and its capacity to undergo a subsequent step was validated by Wulff, who synthesised an... 

Polyimides syntheses starting from dianhydrides (or derivatives such as bis acid-esters) and diamines (or derivatives like silyl- substituted diamine or isocyanate)... 

Luh T. Y., Wong K. T. Silyl-Substituted Conjugated Dienes Versatile Building Blocks of Organic Synthesis Synthesis 1993 349 370... 

The JV-silyl phosphinous amides present some particularities in their reactivity that make these compounds worth commenting on separately. They are stable and can be easily prepared in the usual way by reaction of AT-silyl substituted primary amines or hexamethyldisilazane with halophosphanes [48,49,128,129] or byJV-silylation of the appropriate phosphinous amides [72, 107]. The reductive Ph-P bond cleavage in AT-silyl phosphazenes Ph3P=NSiMe3 by the action of sodium is a peculiar example of preparing Ph2PNHSiMe3 [130]. 

The acyclic oligoynes 23-26 can be cyclized under Friedel-Crafts conditions, i. e. by treatment with AICI3 in CS2, which presumably proceeds via the intermediate tertiary propargylic 27 and )3-silyl-substituted vinylic carbocations of type 28 (Scheme 5). 

Additions of silyl-substituted synthons 965 to nitrones such as 962 a in the presence of LDA result in the products 966 which eliminate the lithium salt of O-tri-methylsilyl-N-phenylhydroxylamine 968 to give the olefins 967a or 967b in 72 and 39% yield, respectively [68, 69] (Scheme 7.20). The intermediate lithium salt 968 dimerizes with elimination of LiOSiMe3 98 to form azobenzene and azoxybenzene 961 [68, 69]. 

In the case of silyl-substituted alkynes (R = MejSi), the initially formed irnine undergoes a subsequent 1,3-sigmatropic silyl shift yielding the corresponding enam-ine (Eq. 4.81). 

Several catalytic systems have been reported for the enantioselective Simmons Smith cyclopropanation reaction and, among these, only a few could be used in catalytic amounts. Chiral bis(sulfonamides) derived from cyclo-hexanediamine have been successfully employed as promoters of the enantioselective Simmons-Smith cyclopropanation of a series of allylic alcohols. Excellent results in terms of both yield and stereoselectivity were obtained even with disubstituted allylic alcohols, as shown in Scheme 6.20. Moreover, this methodology could be applied to the cyclopropanation of stannyl and silyl-substituted allylic alcohols, providing an entry to the enantioselective route to stannyl- and silyl-substituted cyclopropanes of potential synthetic intermediates. On the other hand, it must be noted that the presence of a methyl substituent at the 2-position of the allylic alcohol was not well tolerated and led to slow reactions and poor enantioselectivities (ee<50% ee). ... 

From Free Radicals RR R"E This last synthetic route, involving the one-electron oxidation of the free radicals RR R"E with an appropriate Lewis acid such as PhjC, is one of the best methods for the extremely fast and clean formation of the element-centered cations RR R"E+. Although this approach requires the presence of the radical species as readily available starting materials, the recent synthesis of stable silyl-substituted radicals of the type (r-Bu2MeSi)3E (E = Si, Ge, Sn) (see Section 2.2.4.1.2) made such an approach a rather attractive and easily accessible synthetic route to the stable and free (r-Bu2MeSi)3E+ cations (Scheme 2.6)... 

An important contribution to silylium ion chemistry has been made by the group of Muller, who very recently published a series of papers describing the synthesis of intramolecularly stabilized silylium ions as well as silyl-substituted vinyl cations and arenium ions by the classical hydride transfer reactions with PhjC TPEPB in benzene. Thus, the transient 7-silanorbornadien-7-ylium ion 8 was stabilized and isolated in the form of its nitrile complex [8(N=C-CD3)]+ TPFPB (Scheme 2.15), whereas the free 8 was unstable and possibly rearranged at room temperature into the highly reactive [PhSi /tetraphenylnaphthalene] complex. ... 

Wiberg et al. prepared an TV-silyl substituted iminosilane by means of an N2/NaCl and -LiCl elimination. None of the intermediate products was isolated. The iminosilane was formed in the reaction of azido-di-f-butylchlorosilane and tri-t-butylsilylsodium in dibutyl ether at -78°C.13-16... 

The reaction of [LnM-SiR3]" with transition metal halides or halogeno complexes L mM Xx gives silyl-substituted heteronuclear complexes [Ln(R3Si)M]xM L m [2,5,18]. Stable complexes are usually only obtained if the metal complex fragment M L m is not too sterically demanding and if the resulting M-M bond is not too polar. A few examples are shown in Scheme 3. 

Deliberate and stepwise increase of the nuclearity of polynuclear complexes is possible by condensation reactions between silyl-substituted heteronuclear complexes [Ln(R3Si)M]xM L m and metal halides. Two such examples are shown in Scheme 3 (reaction of MeCp(CO)2(MePh2Si)Mn-HgPh with PhHgCl, and reaction of [MeCp(CO)2(MePh2Si)Mn]2Hg with HgBr2) [18]. 

With solubility as one of the principal problems to obtain structural information, the introduction of lipophilic ligands has been particularly successful, as shown impressively with the silyl substituted [CH(SiMe3)2] and [C(SiMe3)3] ligands.20 Steric bulk has also been applied successfully to reduce the tendency toward aggregation. This has been vividly demonstrated by recent chemistry utilizing terphenyl ligands.21... 

The two main groups of silyl substituted alkane ligands HC(SiMe3)3 and HCH(SiMe3)2 demonstrate significantly different steric demands, and we will discuss the two groups of alkali metal complexes separately. Only select compounds will be discussed. 

The method was also applied to the benzoylation of other aromatic compounds (Tab. 7.7). The benzoylation of benzene itself, volatile and less reactive, seemed more difficult to perform (Tab. 7.7, entry 4). Silyl-substituted aromatics reacted by ipso Si-substitution [77], and were less volatile. With trimethylsilylbenzene, benzoylation occurred with an overall yield higher than for benzene, but the competitive H-substitu-tion was also observed (entry 5). 

The Peterson olefination reaction involves the addition of an a-silyl substituted anion to an aldehyde or a ketone followed by the elimination of silylcarbinol either under acidic (awP -elimination) or basic (syn-elimination) conditions to furnish olefins178. Thus, Peterson olefination, just like Wittig and related reactions, is a method for regioselective conversion of a carbonyl compound to an olefin. Dienes and polyenes can be generated when the Peterson reaction is conducted using either an ,/l-unsaturated carbonyl compound or unsaturated silyl derivatives as reaction partners (Table 20)179. 

Symmetrical cyclic triazines (masked imines) have been used in reaction with diethyl trimethylsilyl phosphite to provide phosphonates bearing silyl-substituted a-aminophosphonates.349... 

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