Acetone silyl enolate

The tropane alkaloid skeleton can be accessed in one pot via domino ene-type reactions of acetone silyl enol ether, the first one of them being intermolecular, with catalytic use of TMSOTf (eq 79). Alternatively, as)mmetric tropinones can be reached by cyclization of 1,3-bis-silyl enol ethers with acyl-iminium triflates. ... 

Difunctional target molecules are generally easily disconnected in a re/ro-Michael type transform. As an example we have chosen a simple symmetrical molecule, namely 4-(4-methoxyphenyl)-2,6-heptanedione. Only p-anisaldehyde and two acetone equivalents are needed as starting materials. The antithesis scheme given helow is self-explanatory. The aldol condensation product must be synthesized first and then be reacted under controlled conditions with a second enolate (e.g. a silyl enolate plus TiCl4 or a lithium enolate), enamine (M. Pfau, 1979), or best with acetoacetic ester anion as acetone equivalents. 

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... 

Re-examination of the photolyses of the family of aryldisilanes PhRR Si—SiMe3 (R,R = Me, Ph) in solution containing acetone was found to give not only the previously observed products believed to be derived from an ene reaction between the silatriene and acetone, 12651, but in addition, and not previously observed, the [2 + 2] siloxetanes, 127, were detected and isolated, as were the silyl enol ethers 128 derived from the simple silene... 

A number of silyl enol ethers of acyl silanes have been produced from alkenes by subjection to 50 atmospheres of carbon monoxide in the presence of 0.1 equivalents of trialkylsilane and 2 mol% of an iridium catalyst (Scheme 26)102. Hydrolysis to the acyl silanes was achieved using hydrochloric acid-acetone. 

Steady-state kinetic analysis of a competition experiment led to the conclusion that the siloxolane is formed by reaction of a vinylsilirane intermediate with acetone, and that the vinylsilirane arises from addition of the free silylene to butadiene. Since silylenes are known to react more rapidly with acetone than with butadiene, the kinetic analysis further suggested that the carbonyl sila-ylide dissociates more rapidly than it rearranges to the silyl enol ether shown in equation 64140. 

Mikami et al. also investigated the addition of ketene silyl acetals. They found that addition of the silyl enol ether of acetone and allylic silanes did not result in the synthesis of substituted l,2-dihydro[60]fullerenes [218a,220], In 1997, Mikami et al. [221] reported the photoaddition of allylic stannanes that leads to monoallylation of C6o (Scheme 13). 

In Equation Si3.7 conversion of cyclohexanone to its silyl enol ether ensures that only acetone acts as the electrophilic partner in a reaction which is equivalent to an aldol condensation of two ketones. 

The reactions of silenes with aldehydes and ketones is another area whose synthetic aspects have been particularly well-studied4,6 7 10 12. The favoured reaction pathways for reaction are generally ene-addition (in the case of enolizable ketones and aldehydes) to yield silyl enol ethers and [2 + 2]-cycloaddition to yield 1,2-siloxetanes (equation 44), but other products can also arise in special cases. For example, the reaction of aryldisilane-derived (l-sila)hexatrienes (e.g. 21a-c) with acetone yields mixtures of 1,2-siloxetanes (51a-c) and ene-adducts (52a-c) in which the carbonyl compound rather than the silene has played the role of the enophile (equation 45)47,50 52 98 99. Also, [4 + 2]-cycloadducts are frequently obtained from reaction of silenes with a,/i-unsaturated- or aryl ketones, where the silene acts as a dienophile in a formal Diels-Alder reaction6 29,100-102. 

The absolute rate constants for ene-addition of acetone to the substituted 1,1-diphenyl-silenes 19a-e at 23 °C (affording the silyl enol ethers 53 equation 46) correlate with Hammett substituent parameters, leading to p-values of +1.5 and +1.1 in hexane and acetonitrile solution, respectively41. Table 8 lists the absolute rate constants reported for the reactions in isooctane solution, along with k /k -, values calculated as the ratio of the rate constants for reaction of acetone and acctonc-rff,. In acetonitrile the kinetic isotope effects range in magnitude from k /k y = 3.1 (i.e. 1.21 per deuterium) for the least reactive member of the series (19b) to A hA D = 1.3 (i.e. 1.04 per deuterium) for the most reactive (19e)41. Arrhenius plots for the reactions of 19a and 19e with acetone in the two solvents are shown in Figure 9, and were analysed in terms of the mechanism of equation 46. 

To a mixture of crystalline anhydrous phosphoric acid (100 mg, 1.01 mmol) and 4-(difluoroiodo)toluene (775 mg, 3.05 mmol) in dry t-butanol (15 ml), under nitrogen, was added the silyl enol ether (6.05 mmol) at room temperature. After 6 h, the mixture was concentrated and the residue was recrystallized from acetone-hexanes to give the title compounds in 79-91% yield. 

Photochemically generated silylenes react with enolizable ketones to give silyl enol ethers. Irradiation of 20 with a low-pressure mercury lamp in the presence of acetone, diethyl ketone, or cyclohexanone gives the re-... 

The silicon-carbon double-bonded intermediates generated photo-chemically from a-alkenyldisilane derivatives react with both enolizable and nonenolizable ketones to give olefins (98). For instance, the photolysis of a-styrylpentamethyldisilane (49) in the presence of one molar equivalent of acetone gives l-trimethylsilyl-2-phenyl-3-methyl-2-butene in 13% yield as a single product. No silyl enol ether to be expected from the reaction of the intermediate with the enol form of acetone is observed. Similar irradiation of 49 with acetophenone affords (E)- and (Z)-l-trimeth-... 

Nucleophilic attack on ( -alkene)Fp+ cations may be effected by heteroatom nucleophiles including amines, azide ion, cyanate ion (through N), alcohols, and thiols (Scheme 39). Carbon-based nucleophiles, such as the anions of active methylene compounds (malonic esters, /3-keto esters, cyanoac-etate), enamines, cyanide, cuprates, Grignard reagents, and ( l -allyl)Fe(Cp)(CO)2 complexes react similarly. In addition, several hydride sources, most notably NaBHsCN, deliver hydride ion to Fp(jj -alkene)+ complexes. Subjecting complexes of type (79) to Nal or NaBr in acetone, however, does not give nncleophilic attack, but instead results rehably in the displacement of the alkene from the iron residue. Cyclohexanone enolates or silyl enol ethers also may be added, and the iron alkyl complexes thus produced can give Robinson annulation-type products (Scheme 40). Vinyl ether-cationic Fp complexes as the electrophiles are nseful as vinyl cation equivalents. ... 

Cationic Pd complexes can be applied to the asymmetric aldol reaction. Shibasaki and coworkers reported that (/ )-BINAP PdCP, generated from a 1 1 mixture of (i )-BINAP PdCl2 and AgOTf in wet DMF, is an effective chiral catalyst for asymmetric aldol addition of silyl enol ethers to aldehydes [63]. For instance, treatment of trimethylsi-lyl enol ether of acetophenone 49 with benzaldehyde under the influence of 5 mol % of this catalyst affords the trimethylsilyl ether of aldol adduct 113 (87 % yield, 71 % ee) and desilylated product 114 (9 % yield, 73 % ee) as shown in Sch. 31. They later prepared chiral palladium diaquo complexes 115 and 116 from (7 )-BINAP PdCl2 and (i )-p-Tol-BINAP PdCl2, respectively, by reaction with 2 equiv. AgBF4 in wet acetone [64]. These complexes are tolerant of air and moisture, and afford similar reactivity and enantioselec-tivity in the aldol condensation of 49 and benzaldehyde. Sodeoka and coworkers have recently developed enantioselective Mannich-type reactions of silyl enol ethers with imi-nes catalyzed by binuclear -hydroxo palladium(II) complexes 117 and 118 derived from the diaquo complexes 115 and 116 [65]. These reactions are believed to proceed via a chiral palladium(fl) enolate. 

Enantiomerically pure 3-oxo-8-oxabicyclo[3.2.1]octyl-2-yl derivatives were obtained by [4 -h 3] cycloaddition of furan with chiral 1,2-dioxyallyl cation engendered in situ by acid-catalyzed heterolysis of enantiomerically pure, mixed acetals derived from 1,1-dimethoxy-acetone and enantiomerically pure, secondary benzyl alcohols [203]. For instance, mixed acetal 439 is converted into the silyl enol ether 440. In the presence of a catalytic amount of trimethylsilyl triflate, 440 generates a cationic intermediate that adds to furan at - 95°C, giving... 

The first aldol can actually be carried out by traditional methods in acid solution condensation occurs on both sides of acetone to give 45, but in alkaline solution 43 is formed in 88% yield. Mukaiyama15 preferred to use the silyl enol ether of acetone 46 with BF3 as the Lewis acid, and this worked as well (89% yield). 

Towards that end,binuclear p-hydroxo complexes 81a,b could be made by the treatment of the diaquo complexes 80a,b with 4 A molecular sieves in acetone. These complexes were expected to prevent the formation of HBF4 when treated with silyl enol ether 83. In the presence of the novel complex 81b (5 mol %), the reaction of silyl enol ether 83 with a-imino ester 82c proceeded smoothly at 25 C to give the acylalanine derivative (S)-84c in 95% yield and 90% ee (Scheme 27). The reaction of other silyl enol ethers with a-imino ester 82c afforded the corresponding acylalanine derivatives with good asymmetric induction (53-84% ee). 

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