Trimethylsilanolate

Trimethylsilyl acetamide [13435-12-6] M 131.3, m 38-43", 52-54 , b 84 /13mm, 185-186 /atm. Repeated distillation in an inert atmosphere, all operations to be performed under anhydrous atmosphere. In the presence of moisture trimethylsilanol (b 31-34 /26mm) is formed and is a likely impurity (check by NMR). [Chem Ber 96 1473 1963.]... 

Polar functional groups such as alcohols or phenols 11 or trimethylsilanol 4 are transformed by monofunctional silylating reagents Me3SiX 12 into their hpophilic and often volatile trimethylsilyl ethers 13 whereas water is converted into persilyl-ated water (=Me3SiOSiMe3, hexamethyldisiloxane, HMDSO, 7, b.p. 100 °C). The persilylation of phenols and, in particular, catechol (or hydroquinone) systems (Scheme 2.1) protects them efficiently against air oxidation even at temperatures of up to 180 °C. (cf, e.g., the silylation-amination of purine nucleosides with dopamine hydrochloride in Section 4.2.4)... 

Silylation of alcohols or phenols 11 with HMDS 2 (compared, e.g., with 22) to their silyl ethers 13 and of trimethylsilanol 4 with HMDS 2 to HMDSO 7 proceeds more slowly, because 2 silylates the alcohols or phenols 11 and 4 apparently via an kineticaUy less favored four-membered cychc transition state 27 (Scheme 2.4). 

Thus removal of water from classical rather inactive fluoride reagents such as tetrabutylammonium fluoride di- or trihydrate by silylation, e.g. in THF, is a prerequisite to the generation of such reactive benzyl, allyl, or trimethylsilyl anions. The complete or partial dehydration of tetrabutylammonium fluoride di- or trihydrate is especially simple in silylation-amination, silylation-cyanation, or analogous reactions in the presence of HMDS 2 or trimethylsilyl cyanide 18, which effect the simultaneous dehydration and activation of the employed hydrated fluoride reagent (cf, also, discussion of the dehydration of such fluoride salts in Section 13.1). For discussion and preparative applications of these and other anhydrous fluoride reagents, for example tetrabutylammonium triphenyldifluorosilicate or Zn(Bp4)2, see Section 12.4. Finally, the volatile trimethylsilyl fluoride 71 (b.p. 17 °C) will react with nucleophiles such as aqueous alkali to give trimethylsilanol 4, HMDSO 7, and alkali fluoride or with alkaline methanol to afford methoxytri-methylsilane 13 a and alkali fluoride. 

Preparation and Properties of Trimethylsilanol and other Trialkyl- or Arylsilanols... 

Because trimethylsilanol 4 is more acidic than methanol or tert-butanol, tri-methylsilanol 4 and hexamethyldisiloxane 7 react rapidly with 12 M NaOH, KOH, or LiOH to give colorless crystalline precipitates of sodium trimethylsilanolate 96... 

Finally, thermochemical data on the heat of hydrolysis of Me3SiCl 14 and of HMDS 2 in 1 M HCI to trimethylsilanol 6 or HMDSO 7 have been measured [30, 31]. 

To mention a few synthetic appHcations of trialkylsilanols, trimethylsilanol 4 adds readily to 2-chloroacrylonitrile in diethyl ether in the presence of triethylamine as triethylammonium trimethylsilanolate followed by ehmination of triethylamine hydrochloride to give 99 [32] (cf. discussion of the strongly nucleophihc properties of ammonium trimethylsilanolate 155 in Section 4.2.1). The stable potassium trimethylsilanolate 97 has also been used for the saponification of esters (Section 4.7). Dimethylphenylsilanol 100 adds readily to a,y9-unsaturated carbonyl compounds such as methyl vinyl ketone 764 in the presence of Pd(OAc)2 in a Heck-Suzuki-type reaction to give the sihcon-free /9-phenylmethylvinylketone 101 [33]. 

As already discussed in Section 2.2, crystalline dimethylsilanediol 53 can be prepared by hydrolysis from hexamethylcyclotrisilazane 51, from dimethoxydimethyl-silane [40], and from octamethylcyclotetrasilazane (OMCTS) 52. The most simple preparation of 53 is, however, controlled hydrolysis of dimethyldichlorosilane 48 in the presence of (NH4)2C03 or triethylamine [41]. Likewise, hydrolysis of hexam-ethylcyclotrisiloxane 54 and of octamethylcyclotetrasiloxane 55 eventually gives rise to dimethylsilanediol 53. In all these reactions the intermediacy of the very reactive dimethylsilanone 110 has been assumed, which can be generated by pyrolytic [42, 43] and chemical methods [44—46] and which cyclizes or polymerizes much more rapidly, e.g. in contact with traces of alkali from ordinary laboratory or even Pyrex glassware [40, 47] to 54, 55, and 56 than trimethylsilanol 4 polymerizes to hexamethyldisiloxane 7. Compound 111 is readily converted into dimethylsilanone 110 and MesSil 17 [46] (Scheme 3.6). 

With stirring and cooling triethylamine (25.3 g) is added dropwise to a solution of trimethylsilanol 4 (22.5 g) and 2-chloroacrylonitrile (22.0 g) in dry ether. The reaction mixture is then stirred for 7-8 h at 30-35 °C. The precipitated triethylammo-nium chloride is removed by filtration, the filtrate is concentrated, and the residue is distilled in vacuo (b.p. 85-86°C/6mm) to give 21.4 g (95%) 2-methoxyacryloni-trile 99 [32] (Scheme 3.15). 

Saponification of Esters or Lactones and Reaction of Persilylated Amides and Lactams with Aikaii Trimethylsilanolates. Conversion of Aromatic Esters into Nitriies by Use of Sodium-HMDS... 

Treatment of methyl p-chlorobenzoate with an equivalent amount of commercial potassium silanolate 97 in abs. diethyl ether affords, after 4h, pure, anhydrous potassium p-chlorobenzoate in 84% yield and methoxytrimethylsilane 13 a. Trimethylsilyl trifluoroacetate reacts hkewise with sodium trimethylsilanolate 96 in THF to give sodium trifluoroacetate, in 98% yield, and hexamethyldisiloxane 7 [119] (Scheme 4.45). 

In the first total synthesis of thromboxane A2, lactone 340 is opened by potassium trimethylsilanolate 97 to give the potassium salt 341 [120]. The potassium salt of the methoxymethyl ether of salicylic acid is prepared likewise [121], as are... 

N-Trimethylsilylamides or lactams 344 react with sodium trimethylsilanolate 96 to generate the anhydrous N-sodium salts 345 and hexamethyldisiloxane 7 in practically quantitative yield [125]. Likewise, silylated succinimide 201 is converted by sodium trimethylsilanolate 96 into hexamethyldisiloxane 7 and the anhydrous sodium salt 346, which reacts with aldehydes RCHO (R=C2H5, n-C Hy), in the presence of catalytic amounts of 96 to give, via 346, the silylated adducts 347 in 43-62% yield [125]. The imide chloride 348 gives, analogously, sodium chloride and 7 and the N-sodium salt 349, which condenses in situ with unreacted imide chloride 348 to give 91% of the amidine 350 [126] (Scheme 4.46). 

Methyl 4-chlorobenzoate (13.65 g, SOmmol) was added in one portion to a stirred slurry of potassium trimethylsilanolate 97 (10.26 g, 80 mmol) in 500 mb dry ether at ambient temperature, under N2. After 4h the white slurry is filtered under N2, washed with ether, and dried under a stream of N2 to afford 13.1 g (84%) analytically pure potassium 4-chlorobenzoate [119] (Scheme 4.62). 

Reaction of pyridine N-oxide 860 with excess allyltrimethylsilane 82 affords, via 947, 2-propenylpyridine 948 in 53% yield as the only reaction product which can be isolated. Ehmination of trimethylsilanol 4 from 947 is apparently followed by fluoride-catalyzed isomerization of 2-allylpyridine into 2-propenylpyridine 948. 3-Methylpyridine-N-oxide 867 a is converted into 2-propenyl-3-methylpyridine in 69% yield. Likewise, fluoride-catalyzed addition of excess benzyltrimethylsilane 83 to 860 furnishes, via 949, 2-benzylpyridine 950 in 70% yield. The generated leaving group trimethylsilanol 4 reacts with excess allyltrimethylsilane 82 or benzyltrimethylsilane 83 in the presence of fluoride to give hexamethyldisiloxane (HMDSO) 7 and propylene or toluene, respectively [60] (Scheme 7.16). 

The liberated trimethylsilanol 4, however, reacts with the trimethylsilyl nitronate... 

Because of the relative instabihty of many trimethylsilyl nitronates 1036, 1037, they should be reacted in situ with olefins 1053 [103-105] or acetylenes [127] to generate the isooxazolidines 1054 [103-105, 107-117, 119-133] or isoxazoles [127] (Scheme 7.37) The isoxazolidines 1054 with R2=H readily ehminate trimethylsilanol 4 in the presence of acids such as TsOH to form the isoxazolines 1055 in high yields [104, 105] (Scheme 7.37 cf. also the cycloadditions with acrylonitrile in Scheme 7.42). 

On reacting nitromethane and acrylonitrile in the presence of TCS 14/triethylamine in benzene (cf. also Scheme 7.42) the oxazolidine 1076, which is obtained in 85% yield, eliminates trimethylsilanol 4 in the presence of TsOH to give 40% d -oxazoline 1077 [104]. Heating of 1076, however, or treatment of 1076 with solid KF leads, via ring opening, elimination of HCN, and rearrangement to d-iso-oxazolidine 1078 in 82% yield this is converted by TsOH, with elimination of 4, into 83% isooxazole 1079 [104]. In contrast with 1076 the isooxazolidine 1080 de-... 

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