Trimethylsilyl acetate

Both aldehydes and ketones react with the anion of ethyl trimethylsilyl-acetate to produce a/3-unsaturated esters in an alternative (13) to the Reformatsky reaction ... 

On the other hand, it has recently been reported (7) that phenyl acetate forms the derived ketene trimethylsilyl acetal by exclusive O-silylation. 

A solution of LD A (0.1 mol) inTHF (75 ml), prepared as above, was then cooled to — 78 °C, and a solution of the TMS carboxylate (0.1 mol) in THF (40 ml) was added with stirring, which was continued at —78 °C for a further 30min. Excess TMSC1 (0.5 mol) was added over 5 min, and the reaction mixture was allowed to come to ambient temperature over 30 min with stirring. It was then filtered by suction through a pad of Celite, and concentrated using a rotary evaporator. The residue was taken up in ether (50 ml), and filtration and concentration were repeated. Distillation of the residue gave the ketene bis(trimethylsilyl)acetals, ca. 90%. 

Benzaldehyde dimethyl acetal 121 reacts, for example, with the silylated allylic alcohol 645, in the presence of SnCl2-MeCOCl, via an intermediate analogous to 641, to the 3-methylenetetrahydrofuran 646 and methoxytrimethylsilane 13 a [182], whereas benzaldehyde dimethyl acetal 121 reacts with the silylated homoallylalco-hol 640 in the presence of TMSOTf 20 to afford exclusively the ds 4-vinyltetrahy-drofuran 647 and 13 a [183]. A related cyclization of an a-acetoxy urethane 648 containing an allyltrimethylsilane moiety gives the 3-vinylpyrrohdine 649 in 88% yield and trimethylsilyl acetate 142 [184, 185]. Likewise, methyl 2-formylamido-2-trimethylsilyloxypropionate reacts with allyltrimethylsilane 82 or other allyltri-methylsilanes to give methyl 2-formamido-2-aUyl-propionate and some d -unsatu-rated amino acid esters and HMDSO 7 [186] (Scheme 5.56). 

Secondary alcohols such as cyclohexanol or 2-butanol also react on heating for 20-120 min at 80 °C with TCS 14 in the presence of BiCl3 to give the chloro compounds cyclohexyl chloride 784 and 2-chlorobutane in 93 and 90% yield, respectively, HCl, and HMDSO 7 [11, 12]. Benzyl alcohol is transformed likewise by Me3SiCl 14 after 120 min. at 80 °C into benzyl chloride in quantitative yield. Analogously, esters such as 2-acetoxypropane 785 are also converted by TCS 14 in 100% yield into chloro compounds such as 786 and trimethylsilyl acetate 142. The yS-lactone 787 gives rise to 788... 

Okamoto, Y. and Sakurai, H., Preparation of (dialkoxyphosphinyl)-methyl-substituted ketone alkyl trimethylsilyl acetal derivatives, Synthesis, 497, 1982. 

Okamoto, Y., Azuhata, T., and Sakurai, H., Dialkyl 3-alkoxy-3-(trimethylsi-loxy)-2-propenephosphonate a one step preparation of (dialkoxyphosphi-nyljmethyl-substituted ketene alkyl trimethylsilyl acetal, Chem. Lett., 1265, 1981. 

Few ketene acetals with electron-accepting substituents are known. Ainsworth et al. (43,44) have described a number of methyl trimethylsilyl acetals (25,... 

Highly enantioselective Mannich-type reactions of A-(2-hydroxyphenyl) aldi-mines with ketene trimethylsilyl acetals and of A-Boc-aldimines with acetyl acetone or furan are catalyzed by chiral phosphonic acids 9 derived from 3,3 -diaryl-(l )-BlNOL and POCI3 (Scheme 12.7). ... 

Monoalkyl ethers of (R,R) 1,2-bis[3,5-bis(trifluoromethyl)phenyl]ethanediol, 24, have been examined for the enantioselective protonation of silyl enol ethers and ketene disilyl acetals in the presence of SnCU (Scheme 12.21) [25]. The corresponding ketones and carboxylic acids have been isolated in quantitative yield. High enantioselectivities have been observed for the protonation of trimethylsilyl enol ethers derived from aromatic ketones and ketene bis(trimethylsilyl)acetals derived from 2-arylalkanoic acids. 

Synthesis of these prolylamide mimics is based on the Peterson olefination between tert-butyl a-fluoro-a-trimethylsilyl acetate and a protected hydroxypentanone. Further introduction of the amino group is rather difficult. This step has been accomplished through conversion of the ester into aldehyde, followed by the formation of the silylated aldimine with LiHMDS, and then the addition of methyl lithium (Figure 7.23). ... 

Dimethylene-2,3-dihydrofuran derivatives, which are produced by fluoride-induced 1,4-conjugative elimination of trimethylsilyl acetate from the [(trimethylsilyl)methyl]-3-furan precursor 207, undergo subsequent [4-1-4] dimerization reactions to produce cycloocta[l,2-3 6,5-. ]difuran derivatives as a mixture of isomers (Equation 137) <1995JA841 >. A methyl substituent at the 3-methylene position was found to retard the rate of dimerization, an observation which is consistent with the proposed two-step mechanism involving the initial formation of a diradical intermediate in the rate-determining step (Table 16). 

Displacement by nucleophiles C—C Bona formation has been accomplished by coupling the syn-3,6-bis(2 -thiopyridyl)piperazine-2,5-diones with ketene trimethylsilyl acetals in presence of silver triflate. There are several interesting features in this extremely useful reaction. The proce-... 

R. Csuk, A. Fiirstner, and H. Weidmann, Branching of ketosugars by ethyl trimethylsilyl-acetate/tetra-n-butylammonium fluoride, J. Carbohydr. Chem. 5 11 (1986). 

Aldol condensation of a-amino silyl ketene acetals (l).10 2-Dibenzylami-noketene trimethylsilyl acetals (1) react with aldehydes premixed with TiCl4 to give a-amino-p-hydroxy carboxylic esters (2) with moderate to high syn-selectivity. Surprisingly, TiCl4-catalyzed reaction of 1 with a chiral a-alkoxy aldehyde proceeds with low asymmetric induction. 

ENOL TRIMETHYLSILYL ETHERS Methylketene methyl trimethylsilyl acetal 2-Oxo-3-trimethylsilyltetrahydro-1,3-oxazole. 

Early work on the GTP mechanism showed that the silyl groups on chain ends rapidly exchange in the presence of anionic catalysts [33, 34]. Without catalyst no exchange occurs [35]. No exchange occurred in the bifluoride catalyzed polymerization of MMA with dimethylphenylsilyl ketene acetal (Scheme 19a) in the presence of dimethyltolylsilyl fluoride [1]. However, in a similar experiment with trimethylsilyl acetate, TBA Ac, and dimethylphenylsilyl ketene acetal, complete exchange occurred within 5 min [36] (Scheme 19b). 

Dimethylketene trimethylsilyl acetals.1 Hydrosilylation of methacrylates with trimethylsilane catalyzed by rhodium(III) chloride results in rearrangement to di-methylketene trimethylsilyl acetals in 65-85% yield. 

Cycloadditions of cyclic ketene trimethylsilyl acetals with ethyl propynoate and other electrophilic alkines were run at room temperature, without a catalyst and solvent-free [47]. 

Synthesis of ethyl (bromo) (trimethylsilyl)acetate (Structure 13)... 

Other nucleophiles such as trimethylsilyl azide or trimethylsilyl acetate reacted in the same way and the azido or acetoxy group was similarly introduced to the aromatic substrate. Phenol ethers incorporating a /i-diketonic moiety at the metaposition underwent an analogous intramolecular aromatic alkylation [24] ... 

Terminal alkenes and cycloalkenes have been found to react in the presence of the polymeric ruthenium complex [Ru2(CO)4(p-OAc)2] with methyl diazo(trimethylsilyl)acetate (Eq. 8) [17]. 

A practical synthesis of 1,3-OX AZEPINES VIA PHOTOISOMERIZATION OF HETERO AROMATIC V-OXIDES is illustrated for 3,1-BENZOXAZEPINE. A hydroboration procedure for the synthesis of PERHYDRO-9b-BORAPHENALENE AND PERHYDRO-9b-PHEN-ALENOL illustrates beautifully the power of this methodology in the construction of polycyclic substances. The conversion of LIMONENE TO p-MENTH-8-EN-YL METHYL ETHER demonstrates a regio-and chemoselective method for the PHOTOPROTONATION OF CYCLOALKENES. An efficient method for the conversion of a ketone to an olefin involves REDUCTIVE CLEAVAGE OF VINYL PHOSPHATES. A mild method for the conversion of a ketone into the corresponding trimethylsiloxy enol ether using trimethylsilyl acetate is shownforthe synthesis of (Z)-3-TRIMETHYLSILOXY-2-PENTENE. 

Peterson olefination. This reaction usually shows little or no selectivity. In contrast, the reaction of ethyl lithio(trimethyIsilyl)acctate with cn-substituted cyclohexanones can show moderate to high (Z)-selectivity. (Z)-Sciectivity is somewhat higher in reaction with ethyl potassio(trimethylsilyl)acetate or t-butyi lithio(trimethylsilyl)acetate, but yields... 

Lower yields are obtained when the anion ol methyl a-(trimethylsilyl)acetate is used in this sequence. 

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