Tris silyl derivates

III derivatives. Anchimeric assistance by J-vinyl, azide and methoxy groups makes tris-silyl derivatives so substituted more reactive than TsiSiMe2l to attack by CF CH,0H, F,CC02H, and Ag salts, while i-02CCFj provides less assistance than iT-OMe. ... 

StericaHy hindered silyl ethers such as ferZ-hutyl dimethyl silyl, / fZ-butyldiphenylsilyl, and tricyclohexylsilyl have been proposed as alternatives to trityl ethers. Reaction of sucrose with 3.5 molar equivalents of ferZ-hutyl dimethyl silyl chloride produces the 6,1/6 -tri-O-silyl derivative in good yield (27). 

Succinimide is readily silylated by HMDS 2 to the N-silylated product 201, which seems, however, to be in equilibrium with the O-silylated derivative 202 a (cf the closely related reactive center in persilylated uridine 3) and reacts after 6-10 days at 24 °C with one equivalent of primary or secondary amines such as morpholine to give the crystalline colorless cyclic acylamidine 203 and HMDSO 7, even in the absence of any protective gas [33] (Scheme 4.12). The reaction is much faster on heating to 120 °C under argon. At these temperatures 201 and 202 a, and possibly also the acylamidine 203, are apparently partially O-silylated by HMDS 2 to the very sensitive 2,5-bis(trimethylsilyloxy)pyrrole 202b or to 2-tri-... 

Examination of neomycin B by a combined G.C.-M.S. procedure has been reported by Murata et all5. G.c. was accomplished with the tri-methylsilyl derivative on a lm column of 1% 0V-1 on Chromosorb W, by which means neomycin was separated from kanamycin. The resulting mass spectra of the neomycin derivative exhibited a minute molecular ion peak at m/e 1550 indicating that all active hydrogens of both hydroxy and amine groups were completely silylated. 

Gas chromatographic separation of amphenicols is further complicated by the need for derivatization of their polar functional groups. Silyl derivatives formed by treating sample extracts with N,O-bis(trimethylsilyl)acetamide (49), trimethylsilyl N,N-dimethyl carbamate (47), N,O-bis(trimethylsilyl)tri-fluoroacetamide/trimethylchlorosilane (99 1) mixture (32, 51), or mixture of... 

If a carbocation or a dication at the same time is also a Hiickeloid An + 2)jt aromatic system, resonance can result in substantial stabilization. The simplest 2jt aromatic system is the Breslow s cyclopropenium ion 206.434 439 Recently, electronic and infrared spectra of the parent ion cyclo-C3H3+ (206, R = H) in neon matrices440 and the X-ray characterization of the tris(trimethylsilyl) derivative were reported.441 The destabilizing effect of the silyl groups was found to be significantly smaller than in vinyl cations. The ion was computed to be more stable than the parent cyclopropenium ion by 31.4 kcal mol1 [MP3(fc)/6-31 lG //6-31G +ZPVE level]. The alkynylcy-clopropenylium ions 207 have been reported recently.442... 

Unsubstituted thieno[2,3-d]pyrimidin-4(3//)-one 2a was converted into the trimethylsilyl derivative 137 by heating in hexamethyldisilazane. Silyl derivative 137 was alkylated at N-3 with l-0-acetyl-2,3,5-tri-O-benzoyl-/3-D-ribofuranose in the presence of stannic chloride in 1,2-dichloroethane or... 

Till now, no tris(silyl)-substituted cyclotetrasilazane is known. Starting with the isomeric unsymmetrically substituted cyclodisilazane (143), the substituent R7 is bonded exocyclically at the four-membered ring of 144 (Scheme 5)103,105. Difunctional halides react with the dilithium derivatives spontaneously and quantitatively, forming a second... 

The condition for the formation of isomers is a side-on coordination of the lithium in 47, the lithium derivative of 27. Depending on the bulkiness of the fluorosilane, this side-on coordination makes possible a substitution that is suitable for the system. In comparison, the reaction of lithiated 27 with iPr2SiF2 leads only to the formation of the tris(silyl)hydrazine 75,16 so that kinetic control of the reaction must be supposed ... 

The silylation of amino acids with BSTFA was studied in detail by Gehrke and coworkers [254—256]. BSTFA—acetonitrile (1 1) was applied first and fourteen amino acids were silylated at 135°C for 15 min. Glu, Arg, Lys, Trp, His and Cys, however, require up to 4 h, in order for measurable peaks to be obtained in the chromatogram. Despite such a long reaction, Gly and Glu gave two peaks and also it was difficult to separate the tris-TMS derivative of Gly from the derivatives of lie and Pro. The influence of polar and non-polar solvents was demonstrated later and was decisive mainly with respect to uniformity of the products. Only the bis-TMS derivative was produced in hexane, methylene chloride, chloroform and 1,2-dichloroethane bis- and tris-derivatives were produced in six more polar solvents. On the other hand, Arg did not provide any peak in the less polar solvents that were used and only one peak in the six more polar solvents. The best and most reproducible results were obtained when silylating seventeen amino acids with BSTFA—acetonitrile (1 1) at 150°C for 15 min 2.5 h at 150°C were necessary for the reproducible derivatization of Gly, Arg, and Glu. These reaction conditions were recommended for the analysis of all twenty amino acids. The TMS derivatives of amino acids were found to be stable on storing them in a sealed vial at room temperature for 8 days, with no decomposition. 

Applications of the method to w-amino acids were discussed and existing knowledge was summarized by Marik et al. [258]. Silylation was executed at 80°C for 1— 2 h or at 90°C for 0.5-1 h, with the use of BSA either alone or with the addition of triethylamine or acetonitrile. BSA alone was recommended as tris-TMS derivatives were produced in practically 100% yield. The presence of amine and solvent led to the formation of bisand tris-derivatives in various ratios, changing with time. However, these conclusions were valid only if the reaction was started with amino acid hydrochlorides. The presence of... 

The direct reaction of (trichloromethyl)chlorosilanes was applied under the same reaction condition described in the direct reaction of elemental silicon with (dichloromethyl)chlorosilanes above. In this reaction, an admixed gases of hydrogen chloride and 40 wt% (trichloromethyl)chlorosilanes in toluene injected using a syringe pump in pre-heater zone was fed into a reactor charged with elemental silicon (90%) and copper catalyst (10%) (Fig. 1). This reaction afforded no tetrakis (chlorosilyl)methane instead, tris(silyl)methanes and bis(silyl)methanes were obtained, which were the same products derived from the reactions of (dichloromethyl)chlorosilanes or chloroform, and (chloromethyl)chlor-osilanes or methylene chloride, respectively. This result may be rationalized by decomposition of (trichloromethyl)chlorosilanes to (dichloromethyl)-chlorosilanes and (chloromethyl)chlorosilanes on silicon-copper contact mass during the reaction, followed by reaction with elemental silicon to afford the products or the decomposition tetrakis(silyl)methane products.16... 

Abstract New polymeric supports, that can be used for preparation of novel catalytic systems, were obtained by grafting poly(vinylmethyl-co-dimethyl)siloxane arms onto multifunctional carbosilane moieties which belong to the class of exceptionally sterically hindered tris(silyl)methanes (Tj,.). Three types of Tj, molecules were applied 3-functional HCCSiMe Br) (type A), 9-functional HC[SiMe2(CHj)j-C (SiMejBr) ] (type B) and 4-functional Tg -derivative [SiMe2C(SiMe2Br)j]j (type C). The periphery-functionalized carbosilane-siloxane materials offer uniformly distributed and accessible sites for coordination of active catalytic species. New catalytic systems were thus prepared by coordination of platinum to vinyl moieties of the reported polymers, and used in hydrosilylation of vinyltrimethylsilane with 1,1,3,3-tetramethyldisiloxane. 

By pyrolysis of a mixture of hydrogen phosphide and silicon hydride, it was Fritz [1] who first succeeded in the preparation of a simple compound with an Si-P bond. About forty years ago, neither the author nor his colleagues anticipated that the silyl phosphane H3S1-PH2 would become the parent compound of a widely used class of starting materials. On the contrary, silylphosphanes remained peculiarities imtil a convenient synthesis of the tris(trimethylsilyl) derivative (Me3Si)3P had been developed [2]. 

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. 

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