Chlorotrimethylsilane with

Aroyl-1 H-1,2-diazepin-3(2//)-ones 27 are obtained80 by demethylation90 of 3-methoxy-l H-1,2-diazepines (vide supra) with chlorotrimethylsilane/sodium iodide. 

The use of an ester as an anion-stabilizing group for a lithiated epoxide was demonstrated by Eisch and Galle (Table 5.5, Entry 11). This strategy has been extended to a,P-epoxy-y-butyrolactone 191, which could be deprotonated with LDA and trapped in situ with chlorotrimethylsilane to give 192, which was used in a total synthesis of epolactaene (Scheme 5.45) [69], The use of a lactone rather than a... 

Substituted 2-butenylboranes 1 can be prepared via the metalation of 9-[(E)-2-butenyl]-9-borabicyclo[3.3.1]nonane with lithium tetramethylpiperidide (LTMP) in tetrahydrofuran at 23 "C followed by treating the resulting anion with chlorotrimethylsilane or chlorotrimethyl-slannanels. 

The preparation of cyclopentadienes with up to four trimethylsilyl groups can be performed easily on a large scale starting with monomeric cyclopentadiene by repeated metalation with n-butyllithium and treating the resulting anion with chlorotrimethylsilane [84], Any complication caused by formation of regioisomers does not occur, since all trimethylsilyl-substituted cyclopentadienes are fluxional by virtue of proto- and silatropic shifts [85], Upon deprotonation with n-butyllithium the thermodynamically most favorable anion is formed selectively (Eqs. 20, 21). Thus, metalation of bis(trimethylsilyl)cyclopentadiene 74, which exists preferentially as the 5,5-isomer, selectively affords the 1,3-substituted anion 75. Similarly, tris(trimethylsilyl)cyclopentadiene 76, which is found to be mainly as the 2,5,5-isomer, affords the 1,2,4-substituted anion 77. 

Historically, the amidinate story begins with the discovery of N,N,N -tris(trimethylsilyl)benzamidine, PhC( = NSiMe3)[N(SiMe3)2], by Sanger. The compound was prepared by the reaction of benzonitrile with LiN(SiMe3)2 followed by treatment with chlorotrimethylsilane. The method was later... 

The diol function of 130 was protected as its acetonide 131 (88 %). Next, the enone function was installed by a-selenation of the enoxysilane, followed by peroxide oxidation and elimination (57 % over two steps). Finally, the unsaturated ketone 132 was homologated by 1,4-addition of trimethylsilylmethyl magnesium chloride, trapping with chlorotrimethylsilane, and reoxidation, to afford the target 117 (88 %). 

Introduction of trimethylsilyl substituents attached directly to the ot-carbon atom of a-(benzotriazol-l-yl)alkyl thioethers provide new opportunities. Thus, treatment of lithiated monosubstituted a-(benzotriazol-l-yl)alkyl thioethers with chlorotrimethylsilane produces a-(trimethylsilyl)alkyl thioethers 837. In reactions with hexamethyl-disilathiane and cobalt dichloride, thioethers 837 are converted to thioacylsilanes 838 that can be trapped in a Diels-Alder reaction with 2,3-dimethylbutadiene to form 2-alkyl-4,5-dimethyl-2-trimethylsilyl-3,6-dihydro-27/-thiopyrans 839 (Scheme 133) <2000JOC9206>. 

As an example, carbon tetrachloride (436) gave tetrakis(trimethylsilyl)methane by reaction with chlorotrimethylsilane in 80% isolated yield. 

The formation of doubly lithiated bis(lithiomethyl)acetylene (107) is accompanied by the formation of 2,3-dilithio-l,3-butadiene (108), when starting from bis(trimethylstanno-methyl)acetylene (106). As reported by Reich and coworkers, the molar ratio X of the two compounds depends on the applied temperature protocol (ratio determined by trapping reactions with chlorotrimethylsilane) (Scheme 37). 

The enantioselective deprotonation of the borane complex 248 of A-methylisoindoline was investigated by Simpkins and coworkers (eqnation 59) . Deprotonation with i-BuLi/(—)-sparteine (11) in diethyl ether at —78°C for 1 h, followed by quenching with chlorotrimethylsilane, yielded the silanes 251, ent-252, 252, ent-25 in a ratio of 86.3 0.4 6.3 7.0 after destroying the chiral centre at nitrogen by treatment of the whole mixture with triethylamine, an e.r. 253/ewf-253 of 86.7 13.3 is expected. 

MeOC6H4, respectively. The titanium enolates were converted into silyl enol ethers 54 by treatment with chlorotrimethylsilane and lithium isopropoxide. Additionally, cyclic enones lb and Ic, and linear enones Id and le, are also good substrates for the asymmetric conjugate addition of phenyltitanium triisopropoxide, giving the corresponding arylation products with over 97% enantioselectivity. 

The reaction of S,N (produced from S,NH and n-butyl-lithium in THF) with chlorotrimethylsilane at —60 C led to the exclusive formation of l,4-SgN2(SiMe3)2. McGlinchey and co-workers have proposed the following mechanism involving the... 

The most convenient synthesis of halogenopyrazines and -quinoxalines is by halogenation of pyrazinones and quinoxalinones with phosphoryl or other acid halides for example, 5-hydroxy-2-pyrazinecarboxylic acid, rather than 5(477)-pyrazinone-2-carboxylic acid, is chlorinated with phosphorus pentachloride/phosphoryl chloride to afford a 63% yield of 5-chloro-2-pyrazinecarbonyl chloride <1994SL814>. Sato and Narita provided an improved synthesis of various halogenopyrazines in which 2(l//)-pyrazinones were activated with chlorotrimethylsilane to give silyl ethers (Section 8.03.7.3). This procedure is most effective for synthesis of bromopyrazines whose overall yields are 62-81% <1999JHC783>. Bromopyrazine is directly prepared by treatment of 2-(l//)-pyrazinone with phosphoryl... 

The feasibility of a deprotonation of cyclohexanone derivatives bearing a chiral heterocyclic substituent in the 4-position with the C2-symmetric base lithium bis[(/f)-l-phenylethyl]amide with internal quenching of the lithium enolate formed with chlorotrimethylsilane is shown in entries 32 and 33 of Table 229,25a. The silyl enol ethers are obtained in a diastereomeric ratio of 79.5 20.5. By using lithium bis[(1S)-l-phenylethyl]amide the two diastereomers are formed in a ratio of 20 80 indicating that the influence of the chirality of the substituent is negligible. 

Enantioselective deprotonation can also be successfully extended to 4,4-disubstituted cyclohexanones. 4-Methyl-4-phenylcyclohexanone (3) gives, upon reaction with various chiral lithium amides in THF under internal quenching with chlorotrimethylsilane, the silyl enol ether 4 having a quaternary stereogenic carbon atom. Not surprisingly, enantioselectivities are lower than in the case of 4-tm-butylcyclohexanone. Oxidation of 4 with palladium acetate furnishes the a./i-unsaturated ketone 5 whose ee value can be determined by HPLC using the chiral column Chiralcel OJ (Diacel Chemical Industries, Ltd.)59c... 

The enantioselectivity of the two-step process (deprotonation and trapping of the enolate) is considerably higher in the case of internal quenching with chlorotrimethylsilane as shown by the results of the external quenching of the lithium enolate with acetic anhydride (Table 4)20. 

Asymmetric elimination in the -hydroxy sulfoximine of bicyclo[3.3.0]octane-2,5-dione monoethylene ketal 3, which is obtained in high yield and diastereoselectivity by addition of (S)-.S -lithiomethyl-A -methyl-S-phenylsulfoximine7, 72 to the latter, by sequential treatment with chlorotrimethylsilane and butyllithium, gives the diastereomeric alkenylsulfoximines (S1)-( )- and (Sy(Z)-4 in a ratio 98 273. 

Deprotonation with alkyllithium and silylation with chlorotrimethylsilane of the sulfide, 2-(l-methyl-2-phenylthioethyl)-l,3-dioxolane (1) gave the antz -diastereomer anti-2-[ R,2S)- -methyl-2-phenylthio-2-trimethylsilyl]-l,3-dioxolane (5a) with very high diastereoselectivity (d.r. 98 2)56. 

Moreover, metalated 2-benzyl-4,5-dihydrooxazoles partially rearrange to ketenimines (10-15%), as is evident from their IR spectra (v = 2018 cm1), as well as trapping with chlorotrimethylsilane 2. 

Since the trapping of the lactam enolate with electrophiles should not be limited to nitroolefins, extension to conjugate additions to alkenylsulfones, the ring opening of N-tosylaziridines, alkylation with functionalized halides, and silylation with chlorotrimethylsilane were explored. 

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