Trialkylsilyl chlorides

Method G Highruiri-selecdvity is also observed in the fluoride-catalyzed reacdonof silyl nitronates v/ith aldehydes. Trialkyl silyl nitronates are prepared in good yield from primary nitroalkanes by consecndve treatment v/ith iithiiim dusopropylamide and trialkylsilyl chloride at -78 C in THF. 

The hydroxyl group was usually protected, because cyanohydrins have tendency to racemization or even decomposition. Vinyl ethers or acetal and acid catalysts furnish acetals [62]. Trialkylsilyl chlorides and imidazole are used to give silyl ethers [63]. Commonly used protective groups are silyl ether, ester, methoxy isopropyl (MIP) ether, and tetrahydro-pyranyl ether. ( -Protected cyanohydrins are tolerant to a wider range of cyanide/nitrile transformations and are utilized widely in the synthesis of compounds of synthetic relevance in organic chemistry. 

Nef reaction.4 Nitro compounds, primary or secondary, are converted to tri-alkylsilyl nitronates in greater than 90% yield by reaction with a trialkylsilyl chloride and DBU in CH2C12. The silyl nitronates derived from secondary nitro compounds are oxidized by C1QH4C03H at 25° to ketones in high yield. This sequence is not useful for conversion of primary nitro compounds to aldehydes. 

Lithium r-butyl(trialkylsilyl)amides, LiN(SiR,)C(CH,)v The t-butyl(trialkylsilyl)amines are prepared by deprotonation of r-butylamine and reaction with a trialkylsilyl chloride yields are 50-70%. They are converted to the corresponding lithium amides by BuLi in THF. 

Scheme 8.13 and Eqs. 8.6-8.10 reveal that lithiated methoxyallene 42 is sufficiently reactive towards a variety of electrophiles such as alkyl halides [44, 45], ethylene oxide [12c], tosylated aziridine 45 [46], dimethyl disulfide [12b], trialkylstannyl and trialkylsilyl chlorides [47, 48] and iodine [49]. These substitution reactions proceed with excellent regioselectivity and the corresponding a-functionalized products are obtained in good to high yields. An exceptional case was found by treatment of 42 with a guanidinium salt, which led to a 60 40 mixture of a- and y-adducts 50 and 51 (Eq. 8.11) [50],... 

Oxiranes undergo ring opening with trialkylsilyl chlorides to yield trialkylsilyl chloroethyl ethers [51]. The reaction has been shown to be catalysed by tetra-n-butylammonium chloride, although most studies have used triphenylphosphine as the catalyst. Substituted oxiranes are cleaved by haloalkanes to yield the corresponding l-ch oro-2-aIkoxy-2-substituted alkanes [52] (see Section 9.3). 

Allenes 185 react with arylmagnesium chlorides in the presence of trialkylsilyl chlorides and a Pd° catalyst, furnishing substituted allylsilanes 186 with high (Z)-stereoselectivity (equation 111). Alkyl halides afford in this reaction mixtures of regioisomeric trisubsti-... 

Perfluoroalkyl iodides reacted with trialkylsilyl chloride in DMF in the presence of zinc followed by hydrolysis with acid to give perfluoroaldehydes in good yields [55]. Recently, Hu reported a new preparation of perfluoroalkyl aldehydes via reaction of perfluoroalkyl halides and DMF, initiated by redox... 

Reactions of trifluorovinyllithium with a variety of electrophiles such as proton, halogen, trialkylsilyl chloride, trialkyltin chloride, methyl iodide, carbon dioxide, sulfur dioxide afforded the corresponding trifluorovinylated derivatives [111, 113,114] (Scheme41). 

Bromo-3,3-difluoropropene reacted with -butyl lithium in the presence of carbonyl compounds or trialkylsilyl chloride to give the corresponding a,a-difluoroallylic derivatives. The difluoroallyllithium was proposed as an intermediate [280-282] (Scheme 96). 

Benzyl, allyl and vinyl halides were electrochemically transformed to their corresponding silanes (52-55) in the presence of trialkylsilyl chlorides as seen in equation 36. 

The answer is to protect the hydroxyl group, and the group chosen here was a silyl ether. Such ethers are made by reacting the alcohol with a trialkylsilyl chloride (here f-butyl dimethyl silyl chloride, or TBDMSCl) in the presence of a weak base, usually imidazole, which also acts as a nucleophilic catalyst (Chapter 12). 

The lithium salts of acyclic secondary amines 92 can be conveniently transformed into the corresponding carbamoyllithiums 89 at —78 °C. Under these reaction conditions they react with trialkyltin chlorides to give carbamoyl stannanes 93 (Scheme 24)98. In the case of benzyl and allyl halides, an alkylation can occur affording products 94. However, when trialkylsilyl chlorides were used as electrophiles no carbamoyl silanes could be detected.. V-Alkyl thiocarbamates 95 can be prepared by reaction of the same intermediates 89 with sulfur followed by. S -alkylation at 0°C (Scheme 24)". 

N,N-bis(trialkyl)ureas react with phenyllithium and trialkylsilyl chloride in refluxing benzene to give the corresponding carbodiimides. ... 

Table 1.2 Various trialkylsilyl chlorides (R sSiCI) used for the protection of R-OH as ROSiR s...

Numerous methods can be used for the synthesis of trialkylsilyl ethers (Scheme 1.27). Alcohols react rapidly with trialkylsilyl chloride (R sSiCl) to give trialkylsilyl ethers (ROSiR 3) in the presence of an amine base like triethylamine, pyridine, imidazole or 2,6-lutidine (Table 1.2). 

Alkynes can be protected as their silyl derivatives and the most common silyl groups TMS, TES, TIPS and TBS are introduced by reacting alkyne with the corresponding trialkylsilyl chlorides (see Table 1.2 for the structures of R sSiCl). 

It was also shown, that dicarbollide ions could be subjected to similar reactions with other electrophilic agents, such as acyl chlorides,14 trialkylsilyl chlorides,15 diphenyl chloro phosphine16 etc., and yield boron sigma-bonded derivatives of dicarba-wufo-unde-caborates. 

Selenium-stabilized carbanions behave as excellent nucleophiles and react with primary alkyl bromides or iodides, allylic and benzylic bromides, epoxides, oxeta-nes, disulfides, trialkylsilyl chlorides, aldehydes, ketones, carbon dioxide, dime-thylformamide, acid chlorides or alkyl chloroformates. With conjugated enones, in the presence of HMPA as cosolvent, the 1,4-addition product is essentially obtained. 

One of the most frequently eneountered reactions is that with proton sources, as observed with arenes (Birch reduction) [189], aldehydes [ 190], alkynes [2d], fullerenes [191], ketones [192] (even enantioselective protonation of ketyl radical anions [193]), nitriles [194], nitro [195] and nitroso compounds [196], and olefins [197]. Protons are often replaced as electrophiles by trialkylsilyl chloride [198],... 

An alternative way to generate a divinylcyclopropane system takes advantage of enolizable carbonyl groups. Trapping of the enolate with trialkylsilyl chloride will usually create the second olefin unit required for a Cope rearrangement. The example of equation (172) demonstrates a sequence of high overall efficiency providing silyl enol ethers which have been hydrolysed to 4-cycloheptenones. The enol ethers should also be versatile intermediates for other transformations. 

When geminal dichloroalkenes obtained from aldehydes are treated with n-BuLi (2 eq) at low temperature, a Fritsch-Buttenberg-Wiechell rearrangement is observed to give lithiated terminal alkynes, which can be readily hydrolyzed or directly reacted with electrophiles such as alkyl halides, trialkylsilyl chlorides, or aldehydes (Scheme 3.88, Table 3.14). 

Based on the relative configuration of the products of Ireland-Claisen rearrangements, two groups have concluded that Z(0)-enolate formation predominates [65,66], On the other hand, two other groups quenched a-alkoxy ester enolates with trialkylsilyl chlorides and found mixtures of enol ether (ketene acetal) isomers [67,68],... 

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