Silation

Other than this system, metallated polysilanes contain the metal in low-valent oxidation states. Such systems have been reported by two groups. In 1995, an alternative functionalization route starting from poly[methyl(H)silylene] or poly[methyl(H)silylene-fo-methylphenylsilylene], 37, was reported, in which the polysilane Si-H moiety was hydro-silated using 1,3,5-hexatriene, affording the diene-modified polymer 67, which was metal functionalized using triiron dodecacarbonyl to give the iron tricarbonyl-polysilane coordination complex, 68.177... 

The catalysts are predominantly modified ZSM-5 zeolite. In general, the modifications are intended to restrict pore mouth size to promote the shape selective production of para-xylene within the microporous structure. The same modifications also serve to remove external acid sites and eliminate the consecutive isomerization of para-xylene. Methods used to modify the zeolite pore openings have included silation [50], incorporation of metal oxides such as MgO, ZnO and P2O5 [51, 52], steaming and the combination of steaming and chemical modification [53]. 

A variation of GTP, referred to as aldol GTP, involves polymerization of a silyl vinyl ether initiated by an aldehyde [Sogah and Webster, 1986 Webster, 1987]. Both initiation and propagation involve nucleophilic addition of the vinyl ether to the aldehyde carbonyl group with transfer of the trialkyl silyl group from vinyl ether to the carbonyl oxygen (Eq. 5-82). The reaction has similar characteristics as GTP. The product is a silated poly(vinyl alcohol) (PVA), which can be hydrolyzed by acid to PVA (Eq. 5-83). 

Other drugs Acetazolamide, acetosulfone, acetylcysteine, acitretin, allopurinol, aminoglutehimide, benzaflbrate, brompheniramine, calcium dobe-silate, chloropheniramine, chlorpropamide, colchicine, deferiprone, dapsone, flutamide, glibenclamide, hydroxychloroquine, mebhydro-lin, meprobamate, metapyrilene, methazolamide, metochlopramide, prednisone, promethazine, retinoic acid, riluzole, ritodrine, tolbutamide, yohimbine... 

A drum of styrene oxide was punctured and the spillage absorbed into an hydrated silate absorbent, the combination swept up and drummed up for disposal. The drum became hot and started emitting copious white fumes. It was not possible to duplicate this behaviour in the laboratory unless acid or base catalyst was also present [1], Absorbents may be inert, epoxides are not but contain considerable strain energy which will be liberated by autoreaction or nucleophilic substitution by, e.g. water. Only a catalyst is needed neither silicates nor floor-sweepings can be guaranteed free of these [2]. 

Useful for such compounds as sugars, phenols, alcohols, amines, thiols, steroids especially recommended for citric acid cycle compounds and amino acids reaction is often carried out in pyridine or dimethyl formamide (the latter being preferred for 17-keto steroids) care must be taken to eliminate moisture lowest silyl donating strength of all common silating reagents... 

D and other phenoxy alkanoic acids Study of conditions for nitration (using N,0-6A-trimethyl silylacetamide), bromination (using 1-2,3,4,5,6 pentafluorobenzene) and silation of phenoxy alkanoic acids prior to GLC [419, 420]... 

Silicon silands — — Silenol converted to trimethyl silated derivatives, then GLC mg L-1 PgL-1 [700]... 

The de novo discovery synthesis of capecitabine (1) was reported by the Nippon Roche Research Center scientists9,19 and was followed up with a preparation invented by a team at the Hoffinann-La Roche laboratories in New Jersey for the conversion to 1 from 5 -DFCR (10).2° In the first route, 5-fluorocytosine (15) was mono-silated using one equivalent of hexamethyldisilazane in toluene at 100 °C followed by stannic chloride-catalyzed glycosidation with known 5-deoxy-l,2,3-tri-0-acetyl-p-D-ribofuranoside (17) in ice-cooled methylene chloride. While this procedure provided the 2, 3 -di-0-acetyl 5-fluorocytidine 18 in 76% yield on a 25-g scale, an alternative method was also devised using in situ-generated trimethylsilyl iodide in acetonitrile at 0°C to provide a 49% yield of 18 on smaller scale. Acylation of the N -amino group of the bis-protected 5 -DFCR derivative was accomplished by the slow addition of two equivalents of -pentyl chloroformate to a solution of 18 in a mixture of pyridine and methylene chloride at -20 °C, followed by a quench with methanol at room temperature to provide the penultimate intermediate 19 on 800-g scale. The yield of intermediate 19 was assumed to be quantitative and was subjected to the final deprotection step, with only a trituration to... 

Sample Preparation Weigh about 0.5 g of sample and reflux with 20 mL of ethanolic 1 N potassium hydroxide solution for 2 h. Reduce the volume of ethanol by evaporation at 45° to 50° in a stream of nitrogen. Add 10 mL of water, and acidify with concentrated hydrochloric acid. Extract the fatty acids from the aqueous phase with successive 20-mL volumes of hexane. Wash the hexane extracts with 20 mL of water, and combine the wash with the aqueous phase. Adjust the aqueous polyol solution to pH 7.0 with aqueous potassium hydroxide solution with the aid of a pH meter. Evaporate to 2 to 3 mL under reduced pressure, and extract three times with 30 mL of boiling ethanol. Filter off any residue, and evaporate the ethanol under reduced pressure to yield a viscous liquid mixture of polyols. Transfer and dissolve 0.1 g of the mixture into a 10-mL capped vial containing 0.5 mL of warm pyridine previously dried over potassium hydroxide. Add 0.2 mL of hexamethyldisilazane, shake, add 2 mL of trimethylchloro-silate, and shake again. Place the vial on a warm plate at about 80° for 3 to 5 min. Check that white fumes are present, indicating an excess of reagent. 

Chalk and Harrod provided the first mechanistic explanation for the transition metal catalyzed hydrosilation as early as in 1965. Their mechanism was derived from studies with Speier s catalyst and provided a general scheme, which could be used also for other transition metals. The catalytic cycle consists of an initial oxidative addition (see Oxidative Addition) of the Si-H bond, followed by coordination of the unsaturated molecule, a subsequent migratory insertion (see Insertion) into the metal-hydride bond and eventually a reductive elimination (see Reductive Elimination) (Scheme 3 lower cycle). The scheme provides an explanation for the observed Z-geometry in the hydrosilation of alkynes, which is a consequence of the syn-addition mechanism. The observation of silated alkenes as by-products in the hydrosilation of alkenes along with the lack of well-established stoichiometric examples of reductive elimination of aUcylsilanes from alkyl silyl metal complexes... 

The main side reaction of the hydrosilation reaction is the dehydrogenating silation reaction. Under certain conditions this reaction can be the main or even the exclnsive reaction. The reaction can occnr, not only with alkenes, bnt also with almost all known substrates. It achieves vinylsilanes from alkenes, silylalkynes from alkynes, and silyl enol ethers from ketones. ... 

The stable, well-characterized copper(I) hydride cluster [(PPh3)CuH]6 is a useful reagent for conjugate reduction of a,p-unsaturated carbonyl compounds. o This hydride donor is chemically compatible with chlorotrimethylsilane, allowing formation of silyl enol ethers via a reductive silation process (Scheme 53). 

Optically active, saturated carbonyl compounds and allylic alcohols were prepared via 1,4- and 1,2-asymmetric hydrosilation of enones using Rh catalysts bearing chiral ligands. For example, 1,4-hydro-silation of a,p-unsaturated ketones afforded the corresponding optically active ketones in 1.4-15.6% ee (Scheme 63). ... 

---