A-Trimethylsilyl ketones

Excess Peterson reagent 1606 a reacts with methyl benzoate, via the intermediates 1609 and 1610, to give, on work-up, some a-trimethylsilylacetophenone 1609 and 49% phenylallylsilane 1611 [15], whereas with 1606a ethyl cyclohexanecarboxylate affords only the a-trimethylsilyl-ketone 1612 [16, 17] (Scheme 10.6). 

The in situ procedure can be used for methylenation or aldehydes and ketones (Peterson reaction) in comparable yields to those previously reported (10, 433), and for conversion of carboxylic acid esters or chlorides into a-trimethylsilyl ketones (equation II).2... 

Cool the solution of BrZnCH2COOEt thus formed to ambient temperature. Charge the dropping funnel with the a-trimethylsilylated ketone 5 (1.98 g, 10 mmol)a dissolved in THF (10 mL), add this solution to the zinc enolate over a period of 10 min, and stir the resulting mixture for 2 h at ambient temperature. 

Trimethylsilyl-l-cyclopentene, 509-510 Trimethylsilyldehalogenation, 514 a-Trimethylsilyl esters, 515 2-Tiimethylsilylethanol, 510-511 /3-Trimethylsilylethyl chloroformate, 471 Trimethylsilylethyl esters, 510 a-Trimethylsilyl ketones, 246 Trimethylsilyllithium, 197,514 a-Trimethylsilyl-2-methylbenzothiazole,... 

Enhanced regioselectivity is obtained when trimethylsilyl enol ethers are prepared by treatment of a-trimethylsilyl ketones with catalytic TMSOTf (eq 7) ... 

Preparative Method the best procedure for the preparation of trimethylsilylacetone is the reaction of trimethylsilyl-methylmagnesium chloride or bromide with acetic anhydride. Other useful preparative methods for a-trimethylsilyl ketones involve the reaction of trimethylsilylmethylmagnesium chloride with acid chlorides, or with aldehydes followed by oxidation of the resulting /3-hydroxysilane to the ketone. When the trialkylsilyl group is very large, particularly the triisopropylsilyl group, a rearrangement from the silyl enol ether to the a-silyl ketone is possible. ... 

Handling, Storage, and Precautions a-trimethylsilyl ketones thermally rearrange to the more stable silyl enol ethers at temperatures above approximately 100 °C and normally within 1 h at 140 °C or above they hydrolyze to the parent ketone upon treatment with acid or base and are difficult to purify by chromatography due to desilylation use in a fume hood. 

The reaction of acid chlorides with 2 equiv of a trimethylsi-lylmethyl organometallic reagent, where the metal can be chloro-magnesium, lithium, or, best, dichlorocerium, proved to be an excellent direct synthesis of allylsilanes via the intermediacy of an a-trimethylsilyl ketone (eq 3). By reaction of a-trimethylsilyl ketones with vinylmagnesium bromide, one can prepare 2-substituted 1,3-butadienes (eq4). ... 

Reaction with Fluoride Ion. The reaction of a-trimethylsilyl ketones with fluoride ion results in attack of the fluoride ion on the... 

The enolate chemistry of a-substituted a-trimethylsilyl ketones can be directed to either side of the ketone. Thus deprotonation with LDA occurs away from the trimethylsilyl side for steric reasons (eq 12), whereas Lewis acid-catalyzed reactions occur on the trimethylsilyl side of the molecule (eq 13). ... 

Reactions of trimethylsilylmethyllithium with secondary and tertiary carboxylic acid methyl or ethyl esters give the corresponding a-trimethylsilyl ketones 45 in... 

Scheme 2.30. Synthesis of a-trimethylsilyl ketones and methyl ketones from esters.

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