Nitrogen-containing silyl derivatives

2- methylphenoxyacetic acid 4 — 2,3,6-trichlorobenzoic acid 5 = 2-(2,4-dichlorophenoxy)propionic acid 6 = (2,6-dichloro-phenoxy)acetic acid 7 = (2,4-dichlorophenoxy)acetic acid 8 = (2,5-dichIorophenoxy)acetic acid 9 = naphthaleneacetic acid 10 = (2,3-dichlorophenoxy) acetic acid 11= (3,4-dichlorophenoxy)acetic acid 12 = (4,6-dichloro-2-methyl-phenoxy)acetic acid 13 = 2-(3,4,5-trichloro-phenoxy)prop-ionic acid 14 = 3-amino-2,5-dichlorobenzoic acid 15 = (2,4, 5-trichlorophenoxy)acetic acid 16 = (4-chloro-2-methyl-phenoxy)butyric acid 17 = (4-chloro-2-oxobenzothiazolin- 

3- yl)acetic acid 18 = (2,4-dichlorophenoxyl)butyric acid. (Reproduced from Ref. 475 with permission). 

Method (i) The alcohol (10 / g) was dissolved in dry pyridine (10 1) and bis(diethylamino)dimethylsilane (2 1) was added. The reaction mixture was then heated for 10 min at 60 °C and cooled and 3-pyridylmethanol (3 y ) was added. The mixture was 

Method (li) The alcohol (10/il) was dissolved in dry pyridine (10 (A) and diethylaminodimethylsilyl-3-pyridylmethanol (5 1 prepared according to the procedure described by Harvey [478] was added. The mixture was heated at 60 °C for 10 min before analysing portions of the reaction mixture directly bv GC-MS. 

The late 1970s and early 1980s saw a period of intense activity in the development and testing of new silyl derivatives. As a result of these efforts, there has been a substantial increase in the range of silyl derivatives available to the analytical chemist since the publication of the original edition of this volume. Research activity and the development of further silyl derivatives appears to have slowed. Surprisingly few of the new derivatives have been adopted for routine use, and trimethylsilyla-tion remains the preferred approach for the vast majority of analytical applications. 

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Addition of Ketene Acetals and Enoles In recent years, much attention has been given to the synthesis of optically active nitrogen-containing compounds, with the key step being the highly stereoselective nucleophilic addition of ketene silyl acetals to nitrones (Scheme 2.174). Similar to nitrone cyanations, in ketene silyl acetal reactions one observes an accelerating effect with thiourea derivatives (633). 

Preparation of calibration standards Seven standard solutions each containing all the target compounds (phenolics plus DIMBOA) were first prepared in HPLC-grade methanol at concentrations of 0.05, 0.1, 0.5, 1.0, 5.0, 10.0, and 20.0 pg/mL respectively. In separate analyses, 1.0 mL from each of the methanolic standards was pipetted into a 2 mL minivial and dried by gentle nitrogen gas blow-down. A 1.0 mL volume of internal standard p-chlorobenzoic acid at a concentration of 1.0 pg/mL in methanol was then pipetted into the dry minivial and dried again by blowdown prior to formation of silylated derivatives. 

Decarboxylation of 117 was effected by treatment of 117 with LiCl in hot, aqueous HMPA at 105 °C providing 118 as a mixture of diastereomers that were separated and carried forward individually. Protection of the secondary amide group as the corresponding methyl lactim ether was accomplished by treating 118 with trimethyloxonium tetrafluoroborate in dichloromethane that contained cesium carbonate. Next, the indole nitrogen atom was protected as the corresponding Boc derivative by treatment with dicarbonic acid bis(rm-butyl)ester in the presence of DMAP and the silyl ether was removed with tetrabutylammonium fluoride to provide diol 119 in 52-78% overall yield from 118. Selective conversion of the allylic alcohol to the corresponding... 

This survey is confined to an overview of group 13 amides containing M-NR2 (R = H, alkyl, aryl, silyl, etc.) groups derivatives where nitrogen is part of a delocalized or polydentate ligand, are not generally covered. However, as in the 1980 book, iminome-tallanes (metal imides) of formula (RMNR ) are treated because of their close relationship to amides and also because of the relevance of the lower derivatives (n= 1, 2 or 3) for possible M N multiple bonding. 

Summary Pure and mixed substituted indoyl-, pyrroyl-, and furanyl-silanes are formed in the reaction of heteroaromatic compounds with lithium alkyls and halosilanes (1-3). Chains of silyl-bridged molecules are available (7). The crystal structure of a lithium derivative (10) is presented and the 1,2-silyl group migration from nitrogen to carbon is proved. Formation of a 16-membered macrocycle (12) containing four indole molecules is described. 

TBDMS derivatives of amino acids. Although quantitative derivatization was achieved with MTBSTFA containing 1% of TBDMCS in DMF by heating at 75 °C for 30 min, two peaks were obtained for arginine. The size of the TBDMS group prevents multiple silylation of the nitrogen atoms. The El mass spectra are sufficiently characteristic to make the TBDMS derivatives very useful for GC-MS analysis, with detection limits at the picomole level [362,364). Methane Cl mass sp>ectra have also been found to be of use in confirming the nature of TBDMS derivatives [3651. 

Activation of C=N Double Bonds. TBDMS triflate has been used to promote additions to, and for the isomerization of, a number of systems containing carbon-nitrogen double bonds. TBDMS triflate is the optimal silyl triflate to promote the Mukaiyama-type vinylogous imino-aldol (Mannich-type) addition of 2-[(f-butyldimethylsilyl)oxy]furan to the IV-benzyl imine derived from (25)-2,3-0-isopropylideneglyceraldehyde (eq 36). ... 

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