Trimethylsilane ethers

Nucleosides are formed from benzyl ethers of ribose or deoxyribose by replacement of the acetal benzyl groups by bromide and coupling with the mercury salts of nucleic bases. The benzyl ether groups are removed by treatment with ammonia (Fischer-Helferich method not shown). In the case of pyrimidine nucleosides, one usually converts the lactams first to aromatic di-trimethylsilane ethers, which then react in high yields with protected halogenoses (Scheme 8.5.4)... 

A solution of the trimethylsilyl enol ether of propionyl trimethylsilane (5 mmol) (Chapter 12) and benzaldehyde diethyl acetal (5 mmol) in dichloromethane (10ml) was added to a solution of BF3.OEt2 (5 mmol) in dichloromethane (5ml), cooled to —78 C. After being stirred for lh at -78°C and 2h at -30°C, the mixture was quenched with excess saturated sodium hydrogen carbonate solution, and extracted with ether. Concentration and distillation gave the product -ethoxy acylsilane, (4.6mmol, 95%). b.p. 105-106 C/2mmHg. Treatment of this alkoxy... 

Cyclohexanone, 23,35 Cyclohexene oxide, 137 Cyclohcxyl methyl ether, 137 l-Cydohexyl-2-methylpropene, 68-9 ( )-l-Cyclohexyl-2-trimethyl ilylethene, 12 (Z)-l-Cyclohexyl-2-trimethylsilylelhene, 12 l-Cydohcxyl-2-trimethylsilylethyne, 12 (2-Cyclohexylidene-eihyl)trimethylsilane, 29 Cyclopentadec-2-ynone, 48 Cydopentadiene, 25 Cyclopentanone, 72 Cyclopentenones, 15 Cyclopropanone, 133... 

The use of trimethylsilyl-based electrophilic catalysts with organosilicon hydrides also promotes the conversion of aldehydes into ethers and avoids the need to employ the potentially hazardous trityl perchlorate salt.314,334,338 One reagent pair that is particularly effective in the reductive conversion of aldehydes into symmetrical ethers is a catalytic amount of trimethylsilyl triflate combined with either trimethylsilane, triethylsilane, PMHS,334 or 1,1,3,3-tetramethyldisiloxane (TMDO, 64) as the reducing agent (Eq. 179).314 Either... 

Equivalent amounts of aldehydes and alkoxytrimethylsilanes react to form unsymmetrical ethers in near quantitative yields in the presence of either trimethylsilane or triethylsilane and catalytic amounts (ca. 10 mol%) of TMSI in dichloromethane.329,333,334,341 The procedure is particularly convenient experimentally when trimethylsilane is used with TMSI because the catalyst provides its own color indicator for the reduction step (color change from deep violet to vivid red-gold) and the only silicon-containing product following aqueous workup is the volatile hexamethyldisiloxane (bp 99-100°). It is possible to introduce trimethylsilane (bp 7°) either as a previously prepared solution in dichloromethane or by bubbling it directly into the reaction mixture. Cyclohexyloxytrimethylsilane and n-butanal react by this method to give a 93% isolated yield of n-butyl cyclohexyl ether (Eq. 183).334... 

Trimethylsilane in pentane is a particularly good system for the TMSI-catalyzed reductive coupling of tertiary alkoxytrimethylsilanes with aldehydes to form sterically crowded tertiary-primary ethers.337 In this way, 1 -(tert-butoxymethyl)-3-methylbenzene is formed in 87% yield (Eq. 184).338 Reaction of terephthaldehyde with two equivalents of the trimethylsilyl ether of 1-adamantanol under these conditions leads to a good yield of the diadamantyl ether of 1,4-benzenedimethanol (Eq. 185).338... 

Nucleophilic Perfluoroalkylation of Nitrones The reaction of a,N-diaryl nitrones with (trifluoromethyl)trimethylsilane (TMSCF3) gives O-trimethylsilyl ethers of a-(trifluoromethyl)-hydroxylamines. This reaction is initiated by potassium ten -butoxide. Removal of the trimethylsilyl group on acid treatment leads to a-(trifluoromethyl)hydroxylamines, whereas catalytic hydrogenation gives a-(trifluoromethyl)amines (Scheme 2.194). 

Silyl enol ethers.1 Aldehydes, ketones, ot,p-enals, and a,p-enones are converted into the silyl enol ethers in moderate to high yield by reaction with iodo-trimethylsilane, generated in situ, and N(C2H5)3 at 25° in acetonitrile. In some cases intermediate stable 1,2- or 1,4- adducts can be isolated. Thus the 1,2-adduct a hag been isolated as an intermediate in the reaction of some aldehydes and shown to decompose to the silyl enol ether. 

Methyl vinyl ether Ether, methyl vinyl (8) Ethene, methoxy- (9) (107-25-5) Chlorotrimethylsilane Silane, chlorotrimethyl- (8,9) (75-77-4) l-(Methoxyvinyl)trimethylsilane Silane, (1-methoxyethenyl)trimethyl- (10) (79678-01-6)... 

The present method offers a more efficient and convenient two-step route to the parent a,B-unsaturated acylsilane derivative. The first step in the procedure involves the conversion of allyl alcohol to allyl trimethylsilyl ether, followed by metalation (in the same flask) with tert-butyllithiura at -75°C. Protonation of the resulting mixture of interconverting lithium derivatives (2 and 3) with aqueous ammonium chloride solution furnishes (1-hydroxy-2-propenyl)trimethylsilane (4), which is smoothly transformed to (1-oxo-2-propenyl)trimethylsilane by Swern oxidation. The acylsilane is obtained in 53-68% overall yield from allyl alcohol in this fashion. 

Mukiayama aldol reactions between silyl enol ethers and various carbonyl containing compounds is yet another reaction whose stereochemical outcome can be influenced by the presence of bis(oxazoline)-metal complexes. Evans has carried out a great deal of the work in this area. In 1996, Evans and coworkers reported the copper(II)- and zinc(II)-py-box (la-c) catalyzed aldol condensation between benzyloxyacetaldehyde 146 and the trimethylsilyl enol ether [(l-ferf-butylthio)vinyl]oxy trimethylsilane I47. b82,85 Complete conversion to aldol adduct 148 was achieved with enantiomeric excesses up to 96% [using copper(II) triflate]. The use of zinc as the coordination metal led to consistently lower selectivities and longer reaction times, as shown in Table 9.25 (Eig. 9.46). 

Methoxymethyl trimethylsilane (trimethylsilylmethyl methyl ether) [14704-14-4] 118.3, b 83°/740mm, d 5 0.758, n2D5 1.3878. Forms an azeotrope with MeOH (b 60°). If it contains MeOH (check IR for bands above 3000cm1) then wash with H2O and fractionate. A possible impurity could be chloromethyl trimethylsilane (b 97°/740mm). [JACS 70 4142 1948]. 

CARBOXYLIC ACIDS Allyltrimethyl-silanc. Bistrimcthylsilyl ether, (, hloro-trimethylsilane. Ilexamethyldisiloxane. 

The use of a Lewis acid (e.g., friethylfluoroborate, zinc chloride, stannous chloride, titanium chloride, iron(m)chloride) and other reagents (e.g., iodine, trimethylsilane, trifluoiomethane-sulfonylsilane) have also been recommended. Exhaustive lists of catalysts and conditions can be found in reviews devoted to carbohydrates [5-7], or to general organic chemistry [27,28], However, one can add the new catalyst, which has been introduced for the smooth formation of p-methoxybenzylidene acetals and p-methaxy-phenylmethyl methyl ether [29], namely 2,3-dichloro-5,6-dicyano-p-benzoquinone (DDQ), and has been applied very recently [30] to the synthesis of isopropylidene mixed acetals. 

Co2(CO)8-catalyzed reactions of benzylic acetates with trimethylsilane and CO proceed under mild reaction conditions to give trimethylsilylethers of /3-phenethylalcohol in 43-76% yield. The highest yields are observed for benzyl acetates with electron-donating substituents.111 Secondary alkyl acetates are also good substrates in the reaction system, yielding enol silyl ethers.112 In addition, the cobalt complex is an effective catalyst for siloxymethylation of five-membered cyclic ortho esters, as shown in Eq. (41).113... 

Carbonyl Addition Diethylzinc has been added to benzaldehyde at room temperature in the presence of an ephedra-derived chiral quat (8) to give optically active secondary alcohols, a case in which the chiral catalyst affords a much higher enantioselectivity in the solid state than in solution (47 to 48, Scheme 10.6) [30]. Asymmetric trifluoromethylation of aldehydes and ketones (49 to 50, Scheme 10.6 [31]) is accomplished with trifluoromethyl-trimethylsilane, catalyzed by a quaternary ammonium fluoride (3d). Catalyst 3d was first used by the Shioiri group for catalytic asymmetric aldol reactions from silyl enol ethers 51 or 54 (Scheme 10.6) [32]. Various other 1,2-carbonyl additions [33] and aldol reactions [34] have been reported. 

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. 

Dichloropropenoyl trimethylsilane, prepared by photochemically induced addition of bromotrichloromethane to the ethyl enol ether of acetyl trimethylsilane, undergoes completely regioselective addition-elimination upon treatment with lithium cyanocuprate reagents, giving the Z -3-chloroalk-2-enoyl silane products (vide supra, Section III.D.3)135. 

Benzyl acetates react with trimethylsilane and CO in the presence of Co2(CO)8 as catalyst to give P-phenethyl alcohols by a one-carbon homologation. The active catalyst is assumed to be (CH3)3SiCo(CO)4. The reaction proceeds under CO at atmospheric pressure at 25°. It fails with benzyl alcohol itself, but is successful with benzyl formate and benzyl methyl ether.5... 

Reactions of polyfluoroalkylchromones with (perfluoroalkyl)trimethylsilanes proceed as a 1,4-nucleophilic per-fluoroalkylation to give 2,2-bis(polyfluoroalkyl)chroman-4-ones with high regioselectivity and good yield after acid hydrolysis of trimethylsilyl (TMS) ethers (e.g., see Scheme 52) <2003JOC7747>. 

Whereas methyl 2-siloxycyclopropanecarboxylates are thermally stable up to temperatures as high as 170 °C, they readily rearrange at low temperatures under the influence of appropriate Lewis acids. Catalytic amounts (0.05-0.4 equiv.) of iodo-trimethylsilane within minutes to days promote a quantitative ring opening of cyclopropanes 755 to the corresponding silyl enol ethers 156 (Eq. 68, Table 4)88). 

---