Substituted trimethylsilane

PVC, polyamides, unsaturated crosslinked polyesters, ABS, and wood . Di- and tri-benzotriazole photostabilizers, such as (874) and (875) are synthesized from 2-nitro-benzenediazonium salts and an excess of 1,3-dihydroxybenzene or 1,3,5-trihydroxybenzene <85Mi 40i-0l>. The dibenzotriazole derivatives (874b and 875b) can be used as polymerizable acrylic UV absorbers <84PB237>. A few or/Ao-urethane and -trimethylsilane substituted 2-phenylbenzotriazoles (876 and 877) show similar photostabilization activity . Weather resistance of low-density polyethylene is improved by the addition of a benzotriazole-type photostabilizer <90M140i-04>. 

Compared to the cyclic ketones, the coupling of aliphatic aldehydes to prepare 3-substituted indoles was less successful, except for phenyl acetaldehyde, which afforded 3-phenyl indole 83 in 76% yield (Scheme 4.22). The lack of imine formation or the instability of the aliphatic aldehyde towards the reaction conditions may be responsible for the inefficiency of these reactions. Therefore, a suitable aldehyde equivalent was considered. With the facile removal of a 2-trialkylsilyl group from an indole, an acyl silane was tested as a means of preparing 3-substituted indoles. Indeed, coupling of acetyl trimethylsilane with the iodoaniline 24 gave a 2 1 mixture of 2-TMS-indole 84 and indole (85) in a combined 64% yield. Evidently, the reaction conditions did lead to some desilylation. Regardless, the silyl group of 84 was quantitatively removed upon treatment with HC1 to afford indole (85). 

Palladium-catalyzed [3+3] cycloaddition of (2-(acetoxymethyl)-2-propenyl)-trimethylsilane with azomethine imi-nes, for example, l-benzylidene-3-oxopyrazolidin-l-ium-2-ides, leading to appropriately substituted hexahydro-7-methylene-177-pyrazolo[l,2- ]pyridazin-l-ones has been reported <2006JA6330>. 

Tris(diphenylmethyleneamino)borane was obtained according to Eq. (30). Exchange reactions of monomeric and dimeric iminochloroboranes with various fluorides could not be effected. However, this lack of reaction is to be expected, since it is well known from borazine chemistry that substitutions which would require a structural change in order to obtain a stable product will not occur 20>. (Diphenylketimino)trimethylsilane (rather than diphenylketimine lithium) has been utilized successfully to prepare (diphenylmethyleneamino) dihaloboranes. This type of reaction is in accordance with earlier observa-... 

Although the oxidation potentials of aldehydes and ketones are generally very high, silyl substitution at the carbonyl carbon results in a significant decrease in the oxidation potential (Table 6) [16] (Sect. 2.3.3). For example, undecanoyl-trimethylsilane exhibits an oxidation wave at the peak potential of 1.45 V. The effect of the silyl-substitution in the oxidation potential of aryl-substituted carbonyl compounds, however, is much smaller [56]. 

Radical addition of dibromodifluoromethane to alkenes followed by sodium borohydride reduction is a convenient two-step method for the introduction of the difluoromethyl group.5 Either one or both carbon-bromine bonds in the intermediate dibromides may be reduced, depending on the reaction conditions. In the case of acyclic dibromodifluoromethane-alkene adducts, the reduction occurs regioselectively to yield the relatively inaccessible bromodifluoromethyl-substituted alkanes. The latter are potential building blocks for other fluorinated compounds. For example, they may be dehydrohalogenated to 1,1-difluoroalkenes an example of this methodology is illustrated in this synthesis of (3,3-difluoroallyl)trimethylsilane. 

Trialkylaryltin derivatives 30 are converted into fluoro-substituted derivatives 31. 37-38 (4-Mcth-oxyphenyl)trimethylsilane (32) in acetonitrile gives 4-fluoroanisole and (3-fluoro-4-meth-oxyphenyl)trimethylsilane in the ratio 1 2. A -Methyldiethanol esters of arylboronic acids 33 (l-aryl-5-methyl-2,8-dioxa-5-azonia-l-boranuidabicyclo[3.3.0]octanes) are converted into tluoroaromatic compounds with cesium fluoroxysulfate in acetonitrile in the presence of 1,3-dinitrobenzene at room temperature.39-40 Regiospecific synthesis of 2-fluoro-3-0-methyles-trone in 27 % yield occurs upon fluorination of the corresponding arylboronic acid with cesium fluoroxysulfate.41... 

Multinuclear NMR data for homologous senes of fluoromethylated malo-nates [72] and trimethylsilanes [97] are compiled in Table 11. In both senes, fluoromethyl attachment is to a quaternary site These compounds are readily synthesized using fluorohalomethanes to incorporate the final fluoromethyl moiety All the malonates, except diethyl methyltnfluoromethylmalonate (4) [93], are isopropyl-substituted diethyl esters [72]. The silane data, with the exception of trimethyltrifluoromethylsilane (5) [95], are from reference 97 Chemical shift data are very comparable, with the malonates having higher proton and fluorine chemical shifts but slightly lower carbon values. The magnitudes of cf and 2J jp coupling are similar for both sets of compounds. 

Recently the unprecedented example of stereoselective C—Si bond activation in cu-silyl-substituted alkane nitriles by bare CQ+ cations has been reported by Hornung and coworkers72b. Very little is known of the gas-phase reactions of anionic metal complexes with silanes. In fact there seems to be only one such study which has been carried out by McDonald and coworkers73. In this work the reaction of the metal-carbonyl anions Fe(CO) (n = 2, 3) and Mn(CO) (n = 3, 4) with trimethylsilane and SiH have been examined. The reactions of Fe(CO)3 and Mn(CO)4 anions exclusively formed the corresponding adduct ions via an oxidative insertion into the Si—H bonds of the silanes. The 13- and 14-electron ions Fc(CO)2 and Mn(CO)3 were observed to form dehydrogenation products (CO) M(jj2 — CH2 = SiMe2) besides simple adduct formation with trimethylsilane. The reaction of these metal carbonyl anions with SiFLj afforded the dehydrogenation products (CO)2Fe(H)(SiII) and (CO)3Mn(II)(SiII). ... 

Photochemically-induced addition of bromotrichloromethane to 1-ethoxy-1-trimethyl-silylethene, the ethyl enol ether of acetyl trimethylsilane, generates a 1 1 adduct which provides 3,3-dichloropropenoyl trimethylsilane (20) on solvolysis. Treatment of this material with lithium alkyl cyanocuprates resulted in addition-elimination to give the -isomers of the 3-substituted a,/J-unsaturated acyl silane products (Scheme 50)135. 

The [4 + 2] cycloaddition of a-phenylselenopropenoyl trimethylsilane (75) with 2,3-dimethylbuta-1,3-diene is unusual in that a significant portion of product mixture consists of the hetero-Diels-Alder dihydropyran adduct 76. The phenylselenenyl substituent appears to be responsible for this unusual pattern of reactivity, since propenoyl trimethylsilane gives only the expected regioisomer (77, X = H) (Scheme 116)14. a-Selenenyl substituted a,/l-unsaturated acyl silanes such as 75 were used to prepare a series of substituted dienes in excellent yields through the addition of a-sulphinyl carbanions, Brook rearrangement and expulsion of sulphinate, in a reaction pathway recognisably more typical of acyl silanes (Scheme 117). 

Phenylthiotrimethylsilane adds to propenoyl trimethylsilane under the influence of Lewis acid to give l,3-bis(phenylthio)-l-trimethylsilylprop-l-ene (18). This enol thioether may be deprotonated with f-butyl lithium and alkylated with any of a large range of electrophiles. Subsequent hydrolysis-elimination with mercuric chloride in aqueous acetonitrile provides -substituted a,/J-unsaturated acyl silanes (vide supra, Section III.D.3)132. It should be noted that, in this transformation, the /1-substituent has... 

Other examples of Si—C(Cp) bond cleavage reactions deal with pentamethylcyclopen-tadienyl (Cp ) substituted silicon compounds. Scheme 11 shows a collection of different kinds of reactions with (pentamethylcyclopentadienyl)trimethylsilane as the substrate. Nucleophilic as well as electrophilic attack is the basis for Si—C(Cp) bond fission97. Reactions with various element halides involved in pentamethylcyclopentadienyl transfer are very useful in synthetic chemistry88-91 (see also Sections II.B and HE). 

Akhrem et al.390 have reported a unique method for the acylation of aromatics. When alkanes and cycloalkanes (propane, butane, cyclopentane, cyclohexane) are treated with CBr4-2AlBr3 in the presence of carbon monoxide, the intermediate acyl cations react with aromatic silanes to yield acylated products by desilylative acylation [Eq. (5.151)]. The ipso-substitution of trimethylsilane takes place regioselectively,... 

In contrast to these results, bromo-trimethylsilane (527) has only ester cleaving properties referring to dialkyl phosphonates (Scheme 85). Via this reagent a great variety of substituted phosphonic acids can be prepared in hitherto unknown yields. 

The carbanions derived from (2-(benzotriazol-l-yl)-2-substituted-ethyl)trimethylsilanes having an acidic /J-proton 242 reacted with non-enolizable aldehydes to afford the corresponding (l-arylalkenyl)siloxymethanes 243 via the 1,4-silyl migration with the elimination of benztriazol-l-yl group (equation 154)385,386. Compounds 242 serve as the synthetic equivalents of a-X-substituted alkenyllithiums. 

Dialkoxymethyllithiums 43 3649 and 434649 651, 2-lithio-l,3-dioxolane 435649 and 2-lithio-1,3-dioxane 436649 are formyl anion equivalents, which have been prepared either by reductive lithiation of 2-(phenylsulfanyl) substituted precursors at —95 °C649 or by trans-metallation of 2-(tri-n-butylstannyl) substituted compounds at —110649 or —78°C651. The starting acyclic phenylsulfanyl precursors can be prepared from the corresponding orthoformates by reaction with (phenylsulfanyl)trimethylsilane and trimethylsilyl triflate as catalyst (for compounds 433 and 434). The cyclic derivatives (435, 436) were prepared from l,2-bis(l,3-dioxolan-2-yloxy)ethane and propane, in the same way649. 

Dichlorofluoromethyl)trimethylsilane and trimethyl(trifluoromethyl)silane react (under the conditions of nucleophilic catalysis by fluoride ions) with compounds containing halogen atoms at C = N or N = groups, e.g. formation of 6 and 7. Such halogen atoms can be easily substituted by dichlorofluoromcthyl or trifluoromethyl groups. 

Lithoxymethylidynephosphane The simple preparation of l-(l,2-dimethoxyethane-0,0 )lithoxy-alkylidenephosphanes from carboxylic esters and (l,2-dimethoxyethane-0,0 )lithium phosphanide (Eq. 8) motivated us to investigate the analogous reaction with carbonic acid esters very carfully. Whereas with the educt (dme)Li-PH2 several, difficult to separate by-products are formed, lithium bis(trimethylsilyl)phosphanide and diethyl carbonate react at 0 °C in 1,2-dimethoxyethane with elimination of two equivalents of ethoxy trimethylsilane to give the heteroatom substituted phosphaalkyne (dme)2Li-0-CsP in a nearly 80 % yield (Eq. 9) [13]. 

Conversion of —Si (013)3 to —OH. Searle chemists have used this transformation in a synthesis of 4-demethoxydaunomycinone (6). Thus aryl-trimethylsilanes were known to be converted into aryl trifluoroacetates by lead tetrakistrifluoroacetate (4, 282-283) the Searle chemists found that this trifluoroacetoxylation was also applicable to benzyltrimethylsilane. With this information and knowing that 1,3-butadienes substituted by trimethylsilyl groups show selectivity in Diels-Alder reactions, they then devised the route shown in the formulation. The first step involved a Diels-Alder reaction to give 3. This product... 

In another application, the totally regioselective direct anodic methoxylation of (45)-pyrimidinone-4-methyl carboxylate obtained from L-2,4-diamino butyric acid followed by diastereoselective substitution of the methoxy group by allyl trimethylsilane can be combined with the follow-up decarboxylative methoxylation of the carboxy function after hydrolysis. A second methoxy group exchange by allyl trimethylsilane yields the C2-sym-metrical (4i ,6i )-4,6-diallyl-pyrimidin-2-one enantiomerically pure [Eq. (50)] [246]. 

Alkenyllithiums generated from trisylhydrazones react with electrophiles such as primary alkyl bromides, aldehydes, ketones, dimethylformamide, CO2, chloro-trimethylsilane, or 1,2-dibromoethane to furnish substituted alkenes, allylic alcohols, a,(3-unsaturated aldehydes, a,P-unsaturated acids, alkenylsilanes, or alkenyl bromides, respectively, as exemplified below for the preparation of an allylic alcohol and an a,P-unsaturated aldehyde. ... 

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