With hexamethyldisilazane

The adsorbent was treated with hexamethyldisilazane in order to methylate the OH group but the 3750 cm-1 hydroxyl band did not decrease appreciably in intensity. Bands did appear due to Si(CHs)s groups and it was concluded that methylation of the hydroxyls, other than those seen in the Raman spectrum, had occurred. 

The use of AMximethylsilylimidazole has been suggested in the reaction with acid chlorides to form imidazolides.[3] In fact, the rate of conversion to imidazolides by reaction of iV-trimethylsilylimidazole with acid chlorides is remarkably rapid even at rather low temperatures. On the other hand, the preparation of the N-trimethylsilylimid-azole from imidazole requires the heating of imidazole with hexamethyldisilazane for several hours. 

Inasmuch as trimethylsilylamine is unstable, it will decompose into ammonia and hexamethyldisilazane. The ammonia thus formed could be visualized to form the amino compound (MegSi)2NB(NHg)-NHSiMe. Since (MegSi) NB(NHSiMe3)2 was prepared Zby Wells and Collins (.13) via Interaction of5 tne chloroborane with hexamethyldisilazane, its production here could follow the same path. 

Golankiewicz et al. <1995JME3558> described a synthesis of the title ring system by ring closure of the five-membered ring. In this case, the pyrimidine compound 253 was treated first with trimethylchlorosilane and, then, with hexamethyldisilazane, and as a consequence of a quite complicated rearrangement the imidazotriazine compound 254 was obtained in excellent yield (80-90%). 

Reaction of (39) with ammonia does not lead to the corresponding enamine, but to the ammonium salt (39 NH4+) that on heating in ethanol or toluene undergoes decomposition into its starting materials. In contrast (47) (R = R2 = H) can be obtained in quantitative yield in the reaction of (39) with hexamethyldisilazane in methylene chloride (87TH2). 

Another work of Duhamel and Ancel [59] related this synthesis of retinal via (3-ionylideneacetaldehyde. Condensation of methallyl-magnesium chloride with diethyl phenyl orthoformate (EtC CHOPh) led after bromination of the ene-acetal, deshydrohalogenation (NaOH 50%), ethanol elimination with hexamethyldisilazane (HMDS) and ISiMes, to the bromo-dienol ether. This latter was submitted to bromine lithium exchange and the lithio enol ether was then condensed with p ionylideneacetaldehyde to give retinal, Fig. (28). 

An additional modification in the above synthetic scheme is possible by introducing the aromatic diamine in the form of its trimethylsilyl derivative [72]. Monotrimethylsilyl-substituted amines are readily prepared from the free amine with hexamethyldisilazane or trimethylsilyl chloride in the presence of a tertiary amine [73, 74] whereas bis(trimethylsilyl)-substituted amines require more aggressive reagents, such as butyllithium in conjunction with trimethylsilyl chloride [75]. As illustrated in Scheme 19, monotrimethylsilyl-substituted amines react with acyl chlorides to form the corresponding amides and liberate trimethylsilyl chloride. Monotrimethylsilyl-substituted amines are reported to display increased reactivity with acyl chlorides [76], This is of great synthetic importance since the increased reactivity allows for reaction with low basicity amines. Bis(trimethylsilyl)-substituted amines, on the other hand, react with acyl chlorides to form the corresponding JV-trimethylsilyl amides, see Scheme 20. The JV-trimethylsilyl amides are much more soluble in common organic solvents. However, they are hydrolytically unstable and readily convert back to the free amides. 

Another possible route to thienamycin (487) has utilized the dipolar cycloaddition of 1-pyrroline 1-oxide (482) with methyl crotonate (79TL4359). The reaction is highly stereoselective due to the operation of secondary orbital effects. The isoxazolidine (483), produced in 90% yield, was subjected to hydrogenolysis, and the resulting amino alcohol (484) was selectively blocked with hexamethyldisilazane to give (485). Treatment with ethylmagnesium bromide then gave /3-lactam (486 Scheme 107). 

However, the uncovered silica surface consisting in residual silanols could induce indesirable competitive reaction from propylene oxide treatment such as epoxide opening and alkoxylation of the surface. In order to overcome these drawbacks, the uncovered surface of the Cl-MTS 3 was previously passivate with hexamethyldisilazane treatment before the ligand 1 was anchored according to scheme 3. 

Primary amides Acyl chlorides react with hexamethyldisilazane in CH2C12 at room temperature to give, after acid hydrolysis, primary amides in 60-90% yield from the carboxylic acid. 

The quantitative analysis was performed with the technique of gas chromato-graphy/mass spectroscopy. A radioactive sample of Cisobitan , which was labelled with 14C at the geminal methyl groups and which was hexadeuterated in the 4,4-dimethyl-siloxy position, was used for this investigation. Silylation of the metabolic products was carried out with hexamethyldisilazane. 

Under acidic conditions, amino-substituted imidazoles and triazoles 135 (X = CH, N) underwent intramolecular nucleophilic substitution reaction to give 136 in yields depending on the C(2 ) substituent orientation <1999CAR190, 1999MI441>. Thiouridine derivative 73 (R = Me) (Scheme 12) cyclized similarly to 72 on treatment with hexamethyldisilazane(HMDS)-ammonium sulfate <1992NN603>. 

There are many silylating reagents for the conversion of an alcohol into the corresponding silyl ether. The reader should consult the Handbook of the Pierce Chemical Co. for an authoritative survey. The procedure for the formation of trimethylsilyl ethers of carbohydrate derivatives with hexamethyldisilazane/ chlorotrimethylsilyl chloride in pyridine and the subsequent examination by g.l.c. analysis is described in Section 2.31. 

A very promising procedure deserves to be mentioned, the reaction of carbon suboxide (592) with hexamethyldisilazane (595)216 which affords in the first step 2,4-dioxo-6-trimethylsiloxy-l-TMS-l,2,3,4-tetrahydro-3-pyridine[N,N-bis(TMS)-car-boxamide] (395) or an isomer of 395 that can directly be converted to yield a variety of piperidine (397, 398, 400) and pyridine compounds (399a, 399b). 392 and 394... 

Specific properties of polysilanes have been linked to the method of synthesis.35 For example, in the case of anionic polymerization of poly[l-(6-methoxy-hexyl)-l,2,3-trimethyldisilanylene] a new type of chromism was induced in the polysilane film by the difference in the surface properties of substrates and was termed a surface-mediated chromism. The polysilane exhibited thermochromism with an absorption maximum at 306 nm at 23°C, but <15°C a band at 328 nm began to appear. A monolayer of the polysilane was transferred onto both a clean hydrophilic quartz plate and a hydrophobic one treated with hexamethyldisilazane by the vertical dipping method. With the hydrophobic plate, a broad UV absorption at 306 nm is obtained, whereas the absorption on a hydrophilic plate shifts to 322 nm. The conformation of the polysilane is preserved by hydrogen bonding between the silica surface and the ether section of the substituent on the hydrophilic plate. The polysilane is attached to the hydrophobic surface only by van der Waals forces, and this weaker interaction would not sustain the thermodynamically unstable conformational state that is attained on the water surface. 

The Frank and Demint [200] method is directly applicable to water samples. After addition of sodium chloride (340g IT1) and aqueous hydrochloric acid (1 1) to bring the pH to 1, the sample was extracted with ethyl ether and the organic layer was then extracted with 0.1M sodium bicarbonate (saturated with sodium chloride and adjusted with sodium hydroxide to pH8). The aqueous solution adjusted to pHl with hydrochloric acid was extracted with ether and after evaporation of the ether to a small volume, Dalapon was esterified at room temperature by addition of diazomethane (0.5% solution in ether) and then applied to a stainless steel column (1.5m/3mm) packed with Chromosorb P (60-80 mesh) pretreated with hexamethyldisilazane and then coated with 10% FFAP. The column was operated at 140°C, with nitrogen carrier gas (30mL muT1) and electron capture detection. The recovery of Dalapon ranged from 91 to 100% the limit of detection was O.lng. Herbicides of the phenoxyacetic acid type did not interfere trichloroacetic acid could be determined simultaneously with Dalapon. 

Anwander and coworkers100 101 silylated the inner surfaces of MCM-41 samples and phases built by co-condensation of TEOS and BTEE with disilazanes of the type HN(SiRR2)2 (R, R = H, Me, Ph, vinyl, n-butyl, / -octyl), whereby the degree of sily-lation depended naturally on the spatial requirements of the silylating reagent. Complete passivation could be achieved with hexamethyldisilazane, which can be used to determine the number of free silanol groups. The vinyl-functionalized MCM-41 samples proved to be very amenable to subsequent surface modification by hydroboration. 

The bis(trimethylisilyl) derivatives 271 resulting from the reaction of thieno[3,2-catalytic amount of ammonium sulfate were condensed with 1-0-acetyl-2,3,5-tri-0-benzoyl-/3-D-ribofuranose in the presence of stannic chloride to furnish, after treatment with methanolic ammonia, the l-(/3-D-ribofuranosyl)thieno[3,2,-d]pyrimidine-2,4-diones 272 and 3-(/3-d-ribofuranosyl)thieno[3,2-d]pyrimidine-2,4-diones 273. 

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