Trimethylchlorosilane-Zinc

Table III. Reductive Coupling of Carbonyls with Zinc and Trimethylchlorosilane...

Benzaldehyde gave modest yields of the coupled product and 15% of trans-stilbene. By using large excesses of zinc and trimethylchlorosilane, the stilbene yield was increased to 36%. Thus far, only 1-indanone has produced high yields, 83%, of the unsaturated dimer(29) ... 

The reaction of dimethyldichlorosilane disproportioning under the influence of aluminum chlorides sharply accelerates on the surface of copper in the presence of methylchloride. In this connection, the process of direct synthesis can encounter the conditions in which the formation of trimethylchlorosilane due to dimethyldichlorosilane disproportioning occurs at noticeable speed, and the quantity of trimethylchlorosilane in the mixture formed can be increased to 20%. At the same time, another reaction accelerates on the surface of copper reacting with methylchloride, the methylation of dimethyldichlorosilane with methylchloride in the presence of aluminum or zinc ... 

Vinyltrimethylsilane (97%), trimethylchlorosilane (98%), chlorodimethylsilane (97%), bromoform (96%), 5-bromo-l-pentene (95%), nBuLi (2.5M solution in hexanes), MeLi (1.6M solution in diethyl ether), n-decane (puriss. p.a., standard for GC, > 99.8%) and hexachloroplatinic(lV) acid hydrate were purchased from Aldrich. Platinum divinyltetramethyldisiloxane complex (Karstedt s catalyst, 3% solution in xylenes), hexamethyl-cyclotrisiloxane (95%), vinylmethyldichlorosilane (97%) and 1,1,3,3-tetramethyldisiloxane (97%) were bought from ABCR. Bromine (puriss) was bought from Eluka. Triethylamine (pure for analysis) and zinc oxide (pure) was purchased from Chempur. Solvents (tetrahydrofurane, diethyl ether, methylene chloride, pentane, ethyl acetate) were supplied by POCh (Polish Chemical Reagents). 

In deuterium-labeling experiments, 4,4-diphenylcyclohexanone (2) reacted with zinc dust/deuterium chloride (prepared from trimethylchlorosilane and deuterium oxide), and gave 4,4-dideuterio-l,l-diphen-ylcyclohexane (3) as the major product (isotopic purity of 81% d2, 10% d, 6% ds and 3% cU equation 7)," while the ketone (4) was converted to (5) in 83% isotopic purity, along with the trideuterio compound (17%), under rather vigorous conditions (equation 8). ... 

For epoxy acetals, a complete reverse in regioselectivity is attained with the zinc/trimethylchlorosilane system as compared with LAH (equation 10). ... 

Kametani s group (84TL4541) discovered that the intramolecular cycloaddition of 1-azadienes prepared in situ from an enamide such as 435 provided a useful tool for the construction of quinolizidines and indolizidines. Heating enamides 435 and 437 in the presence of trimethylchlorosilane, triethylamine, and zinc chloride in toluene at 170-180°C in a sealed tube gave quinolizidines... 

In the first step, the zinc salt of cephalosporin C is produced, followed by the protection of the functional groups (NH2 and COOH) with trimethylchlorosilane. 

Treating succinic anhydrides (64) with triethylamine, zinc chloride and trimethylchlorosilane in acetonitrile gives 2,5-bis(trimethylsiloxy)furans (65). ° The relative ease of silylation in these cases demonstrates one of the differences between enol silyl ether chemistry and classical enolate anion chemistry. It would have been quite difficult to generate the dianion of succinic anhydride. 

Polyacrylate macromonomers were prepared by GTP using zinc halide, triph-enylphosphine, and trimethylchlorosilane. The resulting polymers, having end... 

Oxime ethers are the first of three different types of C=N bonds to be used as radical acceptors. After the cyclization of an alkyl radical onto the oxime ether using zinc-trimethylchlorosilane was first reported by Corey in 1983 [5], n-tributyltin hydride-mediated radical cyclization onto oxime ethers has been successfully applied to the conversion of carbohydrate derivatives to carbocycles (Scheme 1) [6]. Parker employed the oxime ether as the radical trap in the synthesis of the morphine skeleton... 

Preparation. This diene (1) is prepared in 68% yield by the reaction of fra/is-4-methoxybutene-2-one in benzene with trimethylchlorosilane in the presence of anhydrous zinc chloride as catalyst. The reaction is carried out at 40° with stirring overnight. 

Deoxygenation of ketosteroids. The deoxygenation of ketones with this combination has been extended to ketosteroids. -Cholestene can be obtained in about 70% yield from 5a-cholestane-3-one with trimethylchlorosilane and zinc dust in THE at reflux. The reaction fails with 6-, 7-, 12-, 17-, and 20-ketones. This result suggests that a very bulky intermediate is involved. Thus it is possible to selectively deoxygenate diketones. For example, A -Sa-cholestene-... 

Trimethylsilyl enol ether of camphor. The usual methods for preparation of trimethylsilyl enol ethers are unsatisfactory in the case of camphor. However, 3-endo-bromocamphor (1) is converted into the trimethylsilyl enol ether of camphor (2, >80% yield) hy reaction with activated zinc in ether in the presence of trimethylchlorosilane. 

Some salts could not be dehydrated in THF. Iron(III) chloride for example, polymerizes THF and must be prepared using neat trimethylchlorosilane. Cobalt(II) chloride dihydrate gave a similar result requiring neat trimethylchlorosilane. In both cases, nearly quantitative yields of the anhydrous salt were obtained. Hydrated zinc chloride, which we prepared by adding 10 wt % water to the anhydrous chloride because well-defined hydrates are not commercially available, was very efficiently dehydrated in neat trimethylchlorosilane to give a 96% yield of zinc chloride. In contrast, the THF/trimethylchlorosilane mixture afforded a comparatively modest 71% yield of the tetrahydrofuranate. Chromium(III) chloride hexahydrate, on the other hand, could not be completely dehydrated in neat trimethylchlorosilane and required THF for an efficient reaction giving 89% yield of chromium(III) chloride tris(tetrahydrofuran). Our results are summarized in Table I. 

The s)mthesis of e /iro-L-j -hydroxyglutamic acid (844) makes use of the furan heterocycle as a carboxyl equivalent (Scheme 122) [185]. After reduction of 793a to 839 and acetylation (840), the aminal acetate and furan are coupled in the presence of zinc bromide and a catalytic amount of trimethylchlorosilane to give a 67 33 mixture of 841 and 842. In the absence of silane the reaction requires 12 h at room temperature for completion, but with silane present the reaction time is reduced to2hat —15°C. 

Di- and Tetra-hydrothiophens.—Birch reduction of thiophen-2-carboxylic acid with three equivalents of lithium in liquid ammonia gave 2,5-dihydrothiophen-2-carboxylic acid and several other products. When the Birch reduction was carried out with five equivalents of lithium and with methanol as the proton source, a single product, c/s-5-mercaptopent-3-enoic acid, was obtained. Birch reduction of t-butyl 5-t-butylthiophen-2-carboxylate gave the 2,5-dihydro-derivative upon treatment with zinc dust and trimethylchlorosilane and then quenching with molar sodium hydroxide, this gave a mixture of (123) and (124) in the proportions 1 8. ... 

Corey EJ, Pyne SG (1983) Conversion of ketones having 6, c-tt-frmctions to cyclopentanols by zinc-trimethylchlorosilane. Tetrahedrrai Lett 24 2821-2824... 

Cyclization of difunctional compounds is illustrated by the acyloin condensation of diesters (Fig. 19), conventionally performed with sodium in refluxing solvents, and improved by the presence of trimethylchlorosilane. A practical improvement was made with the use of technical-grade TMSCl and ultrasonically dispersed sodium.Thus, the reaction occurs at 0°C in 0.5 to 3 h. An experimental description is given in Ch. 9, p. 331. A chiral center at the a-position of the carbonyl does not suffer racemization. With p-halo esters, cyclizations lead to cyclopropyl derivatives in high yields, except with sterically hindered substrates. A similar reaction occurs with zinc and oxazabutadienes substituted by trifluoromethyl groups, with a fluoride ion as the leaving group (Eq. 15).ii ... 

Trimethylchlorosilane. The use of trimethylchlorosilane (TMSCl) as an activator for reactions of metallic zinc (5 molar equivalents of TMSCl and 10 molar equivalents of Zn in diethyl ether) was recently introduced [80] in the following reaction ... 

With Trimethylchlorosilane. Rather recently [60] it was found that activation of zinc with TMClSi augmented the yield of Zn-Barbier reactions with allylic halides considerably. This unexpected activation by the silane was found earlier for Reformatsky reactions with ethyl 2-bromopropanoate [61] also trimethylchlorosilane-activated lead was applied in Pb-Barbier reactions with crotyl bromide [62] and allyl bromide [63]. 

Carbonyl groups as in quinones or a-diketones can be reduced on sonication with zinc in presence of trimethylchlorosilane. The Clemmensen reduction can also be carried out by sonication in better yields. ... 

Zinc trimethylchlorosilane Ethylene derivs. from ketones s. 17, 933 suppl. 29... 

Apart from lithium derivatives of N-allenylpyrrole, potassium, copper (1), and zinc derivatives have been tested in the reaction with trimethylchlorosilane. Copper and zinc compounds are easily prepared from organolithium ones by the exchange with the corresponding salts in THE Potassium derivatives (apparently. 

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