Trimethyl silyl enolate

Other methods for a-hydroxy ketone synthesis are addition of O2 to an enolate followed by reduction of the a-hydroperoxy ketone using triethyl phosphite 9 the molybdenum peroxide-pyridine-HMPA oxidation of enolates 10 photooxygenation of enol ethers followed by triphenylphosphine reduction 11 the epoxidation of trimethyl silyl enol ethers by peracid 1 - the oxidation of trimethylsilyl enol ethers by osmium tetroxide in N-methylmorpholine N-... 

Selective opening of allylic epoxides (9, 329-330). The reaction of the trimethyl-silyl enol ether (I) of a, /Tepoxycyclohexanone with lithium dimethylcuprate (or di-n-butylcuprate) in THF proceeds as expected to give 2.25,26 However when the reaction is conducted in ether, 2 and 3 are formed in about equal amounts.26... 

Pyridine-/V-oxidc is an efficient Lewis-base catalyst for aldol reactions of trimethyl-silyl enolate with both aryl and alkyl aldehydes in DMF at room temperature, tolerating a wide variety of sensitive substituents in the substrate.160... 

Scheme 9.10 Mannich-type reaction with trimethyl silyl enolate as substrate...

Noteworthy is the identification of the intermediate 52 in the oxidation of the trimethyl silyl enolate of cyclohexanone with photoactivated chloraniF. Compound 53 has been isolated and characterized by X-ray diffraction methods . 

Sometimes a Lewis acid such as zinc iodide is added in catalytic amounts. Side reactions may sometimes occur if acyl cyanides carry hydrogen atoms in the a-position and are, therefore, enolizable. In those examples trimethylsilyl chloride, which is formed during the reaction, may react to give trimethyl-silylated enol ethers (8). This methodology can be applied successfully to the synthesis of such com-... 

It has been shown that trimethyl silyl enol ether of cyclohexanone with benzaldehyde occurs in water in presence of TiCl, in heterogeneous phase at room temperature and atmospheric pressure (Scheme 50). 

Thermal Reactions.— Vinylcyclopropanes and Related Compounds. The trimethyl-silyl enol ether-vinylcyclopropane rearrangement has been extended to bicyclo-[n,l,0]alkane systems (n = 3—5). With the silyl enol ether at the 1-position... 

Several papers have appeared this year describing the oxidation of trimethyl-silyl enol ethers leading to various different products depending on the reagent used. Mo02(acac)2-Bu OOH, for example, results in cleavage of the C—C bond and formation of two carboxylic acids (or a ketone and an acid in the case of a trisubstituted enol ether).A method for the a-hydroxylation of ketones... 

An even more direct approach to these ketones can be expected from the trimethyl silyl enol ether 50 and indeed, as shown above, the dimethyl cuprate provided 49 at —20°, while the mixed cuprate led to 51 at —40° [16]. 

An efficient two-step annelation of functionalized orthoesters with trimethyl-silyloxyfuran derivatives has been reported that produces bicyclo[3. .0]lactones. ° The reaction in Scheme 7 shows an example in which the initial condensation between silyl enol ether and orthoester is followed by the radical cyclization reaction under standard conditions. It is worth underlining the complete diastereocontrol in which three contiguous stereocenters are generated in one step with >95% stereoselectivity. 

Adapted from Sasidharan and Kumar (257). Reaction conditions catalyst, 150 mg methyl trimethyl-silyl dimethylketene acetal (silyl enol ether), 10 mmol benzaldehyde, 10 mmol dry THF as dispersion medium, 10 mL temperature, 333 K reaction time, 18 h. Yield refers to the isolated product yield. Moles of product per mole of metal per hour. b The metal atom is substituted in the tetrahedral position. 

The efficiency of the amination methodology of enolates with 0-phoshinylhydroxyl-amine-type reagents was further demonstrated by Boche and Schrodt in the high-yield amination of 0-(trimethylsilyl)cyanohydrin anions with 4c (Scheme 44)". 0-(Trimethyl-silyl)cyanohydrins prepared by treatment of aryl, hetaryl and conjugated aldehydes with trimethylsilyl cyanide were lithiated to the eniminates. This is a practical method that enables the easy conversion of aldehydes to iV,Ai-dimethylamides under mild conditions. 

Several examples of Bi(0Tf)34H20-catalyzed Mannich-type reactions of various A-benzyloxycarbonylamino sulfones 1 with silyl enol ethers are summarized in Table 5. A-Benzyloxycarbonylamino sulfones 1 derived from differently substituted benzaldehydes were reacted with trimethyl(l-phenylvinyloxy)silane in dichloromethane at room temperature. The corresponding (3-amino ketones 24 were smoothly obtained (Table 5, entries 1-6). The reaction was efficient using electron-deficient benzaldehyde-derived sulfones, and the corresponding (3-amino ketones 24... 

Trimethyl(prop-l-en-2-yloxy)silane afforded (3-amino ketone 24u in good yield (Table 5, entry 10). Silyl enol ethers derived from 3-pentanone and cyclopentanone smoothly afforded (3-amino ketones 24v and 24w, respectively (Table 5, entries 11 and 12). Tetrasubstituted silyl enol ethers readily produced the expected products 24x and 24g (Table 5, entries 13 and 14). 

Table 1 summarizes the results of the reactions of ynoates (2a-c) with a silicon enolate (silyl ketene acetal) and a lithium enolate of methyl propionate (Eq. 1). Except for the reaction of 2c, Fe-Mont catalyzed exclusive 1,2-addition of silyl ketene acetal to 2a and 2b to give an adduct of 3 in high yields. However, even trimethyl silyl trifluoromethanesulfonate (TMSOTf), a generally applied homogeneous strong acid, failed to effect the addition reaction. 

For the use of lithium and sodium bis(trimethyl-silyl)amide respectively in carbonyl enolate chemistry see Barton (reference 15). 

To develop new electrophilic reagents, Ricci and coworkers have described the synthesis of trimethylsilyloxy and hydroxy compounds from magnesium enolates and bis(trimethyl-silyl)peroxide. Magnesium enolates, generated using magnesium diisopropylamide, (DA)2Mg, give the hydroxycarbonyl compounds in excellent yields (equation 72, Table 8). 

ACETONE TRIMETHYLS ILVL ENOL ETHER SILANE, (ISOPROPE NYLOXY )TR IMETHYL SILANE, TRIMETHYL[(1-METHYLETHENYL)0XY]- (1833-53-0), 65, 1 Acetonitrile, purification, 66, 101 Acetophenone Ethanone, 1-phenyl- (98-86-2), 65, 6, 119 Acetophenone silyl enol ether Silane, trimethyl[(1-phenylvinyl)oxy] Silane, tririethyl[(l-phenylethenyl )oxy]- (13735-81-4), 65, 12 4-ACET OXYAZET ID IN-2-ONE 2-AZET IDINONE, 4-HYDROXY-ACETATE (ESTER) 2-AZET ID1N0NE, 4-(ACETYL0XY)- (2 8562 - 53-0), 65, 135 Acetylene Ethyne (74-86-2), 65, 61... 

Acetophenone Ethanone, 1-phenyl- (98-86-2), 65, 6, 119 Acetophenone silyl enol ether Silane, trimethyl[(1-phenylvinyl)oxy]- ... 

The nucleophilic reactivities of silyl enol ethers (58, R1 = alkyl) and silyl ketene acetals (58, R1 = 0-alkyl) have been measured for the triphenylsilyl (R2 = H5) substrate, and its perfluoro analogue (R2 = F5), using benzhydrylium cations as reference electrophiles.224 The triphenyl compound is 10 times less reactive than its trimethyl equivalent, but the perfluorination causes the C=C nucleophilicity to drop by 3-4 orders of magnitude. The new compounds have been placed on scales of nucleophilicity taken from the literature. 

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