Trimethylsilyl ketene

Trimethylsilyl enol ethers, 94,133 Trimethylsilyl ketene acetals, 112-113 3-Trimethylsilyl -lactam, 71 Trimethylsilyl lithium, 51-2... 

Nitrobenzene reacts with the O-trimethylsilyl ketene acetal 663 in the presence of tris(dimethylamino)sulfur(trimefhylsilyl)difluoride (Me2N)3S(Me3SiF2) (TASF) to give the O-silylated adduct 1007 a, which can be oxidized in situ, e. g. by bromine, to give the 4-substituted nitrobenzene 1008 in an overall yield of 79% [87] (Scheme 7.28). With less hindered ketene-acetals, however, mixtures of ortho- and para-substituted nitrobenzenes are obtained. Yet, on reaction of 4-fluoronitroben-zene with the cyclic O-trimethylsilyl ketene acetal 1009 the ortho-substitution product 1010 is obtained in 79% yield [87]. 

Treatment of benzoylisocyanate 1562 with trimethylsilyl ketene 1563 gives the oxazine 1564 which reacts, e.g., with enamines 1565 to give pyridine-2-ones 1567,... 

The trimethylsilyl ester of a-trimethylsilyacetic acid 1613 is converted by LDA and TCS 14 into the C,0,0-tris(trimethylsilyl)ketene acetal 1614 in 91% yield. Reaction of 1614 with benzaldehyde in the presence of ZnBr2 proceeds via 1615 to afford a high yield of trimethylsilyl cinnamate 1616 [18], which gives on work-up free ( )-cinnamic acid in nearly quantitative yield (Scheme 10.7). In contrast, reaction of the lithium salt of 1613 with benzaldehyde then acidic hydrolysis affords a 1 1 mixture of ( )- and (Z)-cinnamic acid in 86% yield [18]. 

Ireland-Claisen rearrangement of O-allyl-O -trimethylsilyl ketene acetals... 

Similar chelation effects are present in a-alkoxymethyl derivatives. Magnesium enolates give predominantly the Z-enolate as a result of this chelation. The corresponding trimethylsilyl ketene acetals give E,Z mixtures.248... 

Tocopheryl)propionic acid (50) is one of the rare examples that the o-QM 3 is involved in a direct synthesis rather than as a nonintentionally used intermediate or byproduct. ZnCl2-catalyzed, inverse hetero-Diels-Alder reaction between ortho-qui-none methide 3 and an excess of <2-methyl-C,<9-bis-(trimethylsilyl)ketene acetal provided the acid in fair yields (Fig. 6.37).67 The o-QM 3 was prepared in situ by thermal degradation of 5a-bromo-a-tocopherol (46). The primary cyclization product, an ortho-ester derivative, was not isolated, but immediately hydrolyzed to methyl 3-(5-tocopheryl)-2-trimethylsilyl-propionate, subsequently desilylated, and finally hydrolyzed into 50. 

Due to their electron deficient character, pyridines are susceptible to nucleophilic attack. Rudler et al. has studied the reaction of pyridines with bis(trimethylsilyl)ketene acetals <06TL4553 06TL4561>. In one instance, they examine the reaction of... 

The PET-oxidative cyclization of unsaturated O-alkyl-O-trimethylsilyl ketene acetals 23 and 27 yields cyclic esters 24, 25, and 28, accompanied by the formation of considerable amounts of non-cyclic esters 26 and 29, respectively [89], The cyclization mode is found to be in accordance with free radical cyclizations of the appropriate esters 26 and 29, performed by heating with organic peroxides [90]. Since organic electrochemistry can be used to oxidize... 

Rearrangement of allyl trimethylsilyl ketene acetal, prepared by reaction of allylic ester enolates with trimethylsilyl chloride, to yield Y,5-unsaturated carboxylic a-cids. The Ireland-Claisen rearrangement seems to be advantageous to the other variants of the Claisen rearrangement in terms of E/Z geometry control and mild conditions. 

Song and co-workers have taken a variety of aldehydes 344 and treated them with A -adamantyl carbene 1 and trimethylsilyl ketene acetal 345 to produce Mukaiyama aldol products 346 in good yield (Eq. 34) [170], The carbene presumably acts as a Lewis base to activate the silicon - oxygen bond in order to promote reactivity of the enol silane. The catalyst loading can be reduced to as low as 0.05 mol% without a change in yield. 

The use of an unsubstituted heterocycle as a precursor in synthetic reactions is relatively rare. For this reason, the reaction described in Equation (120) is shown. Unsubstituted pyrazine 335 is first treated with bis(trimethylsilyl)-ketene acetals, followed by treatment with methyl chloroformate. The result is the nonaromatic products 336 <2005EJO3724, 2005TL3449>. 

A stereoselective Mukaiyama-type aldol reaction of bis(trimethylsilyl)ketene acetals produces silyl aldols with syn stereoselectivity, predominantly due to steric effects.23... 

For a stereoselective aldol of bis(trimethylsilyl)ketene acetals,23 see Reactions of Ketenes earlier. 

The experimental study was carried out with two different imines a standard one, n-hesanaldimine, and an electron-poor one, n-butyl glyoxylate imine. The Scheme 34 shows that the formation of the (3-lactam occurred only when the glyoxylate imime and BF3-Et20 reacted with (trimethylsilyl)ketene. 

Twenty years have passed since DuPont announced a startling new process for polymerization of methacrylate monomers [1]. The method uses a trimethylsilyl ketene acetal initiator catalyzed by nucleophilic anions. It operates at 80 °C and gives unprecedented control over polymer chain architecture (Scheme 1). 

As shown in Scheme 1, GTP converts methacrylate monomer to a polymer with one end group corresponding to the R on the initiator and the other end a trimethylsilyl ketene acetal. If the initiator contains a vinyl group not reactive to GTP, a macromonomer results [8]. The silyl ketene acetal end can be used to initiate another monomer, for example butyl methacrylate, to give... 

More stable alternatives to ketene that have been used in 2-oxetanone synthesis are (trimethylsilyl)ketenes 100 <1996CC1053>. Using methylaluminoimidazolines as catalysts, with aldehydes and 100, 3-(trimethylsilyl)oxetan-2-ones (101a and 101b) were generated with up to 83% ee (Equation 36). 

A diastereoselective Mukaiyama aldol lactonization between thiopyridylsilylketene acetals and aldehydes was used to form the /3-lactone ring in the total synthesis of (-)-panclicin D <1997T16471>. Noyori asymmetric hydrogenation was a key step in a total synthesis of panclicins A-E and was used to establish the stereocenter in aldehyde 140, which in turn directed the stereochemistry of subsequent reactions <1998J(P1)1373>. The /3-lactone ring was then formed by a [2+2] cycloaddition reaction of 140 with alkyl(trimethylsilyl)ketenes and a Lewis acid catalyst. 

E)-a.,fl-Unsaturated acids. Zinc bromide is the most effective Lewis acid for promoting a reaction of C,0,0-tris(trimethylsilyl) ketene acetal (1) with aldehydes (but not ketones) to form a,p-unsaturated acids. The ketene acetal can be prepared as shown in equation (I). 

The use of substituted pyridines in organic synthesis has broad application. The activation of the pyridine ring toward nucleophilic attack is well known in the literature. The products of such reactions are often dihydropyridines which can serve as intermediates in more complex synthetic strategies. Rudler and co-workers have reported on the nucleophilic addition of bis(trimethylsilyl)ketene acetals to pyridine (26). The 1,4-addition product 27 was then cyclized with iodine to afford bicycle 28 in 90% overall yield <02CC940>. Yamada has elegantly shown that facial selectivity can be achieved and chiral 1,4-dihydropyridines accessed in high yield and de (29—>30) <02JA8184>. 

Roush WR, Hall SE (1981) Studies on the total synthesis of chlorothricol-ide stereochemical aspects of the intramolecular Diels-Alder reactions of methyl undeca-2,8,10-trienoates. J Am Chem Soc 103 5200-5211 Rudler H, Denise B, Xu Y, Parlier A, Vaissermann J (2005) Bis(trimethylsilyl)-ketene acetals as C,0-dinucleophiles one-pot formation of polycyclic y-and 8-lactones from pyridines and pyrazines. Eur J Org Chem 3724-2744 Sekino E, Kumamoto T, Tanaka T, Ikeda T, Ishikawa T (2004) Concise synthesis of anti-HIV-1 Active (+)-inophyllum B and (+)-calanolide A by application of (-)-quinine-catalyzed intramolecular oxo-michael addition. J Org Chem 69 2760-2767... 

Table 2 Oxazocines 109 synthesized from pyridines, bis(trimethylsilyl)ketene acetals, and methyl chloroformates <2002CC940, 2005EJO3724>...

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