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Silyl enol ethers cross-coupling reactions

Bis(tetrabutylammonium)ceriuml IV i Oxidative cross-coupling. a-Stan dation, and the resulting free radicals cai uch as silyl enol ethers and allylsilanei reaction. Note that a-germanylalkanoic e the a-silylalkanoic esters do not undergo... [Pg.52]

Silyl enol ethers can be dimerized to symmetrical 1,4-diketones by treatment with Ag20 in dimethyl sulfoxide or certain other polar aprotic solvents.465 The reaction has been performed with R2, R-1 = hydrogen or alkyl, though best yields are obtained when R2 = R1 = H. In certain cases, unsymmetrical 1,4-diketones have been prepared by using a mixture of two silyl enol ethers. Other reagents that have been used to achieve either symmetrical or cross-coupled products are iodosobenzene-BFy-EtiO.466 ceric ammonium nitrate,467 and lead tetraacetate.m If R1 = OR (in which case the substrate is a ketene silyl acetal), dimerization with TiCL, leads to a dialkyl succinate (32, R1 = OR).4 9... [Pg.1204]

Silyl enol ethers undergo cross-coupling with allylsilane in the presence of a Lewis acid. For example, an oxovanadium(V) complex can induce such condensation reactions (equation 81)150. [Pg.1822]

Diones,1 CAN effects cross-coupling between 1,2-disubstituted silyl enol ethers and a 1-substituted silyl enol ether to give a 1,4-dione. The reaction involves oxidation of 1 to a (1-oxo radical,R CHCOR2, which adds to the 1-substituted silyl enol ether (2) to form an adduct that is oxidized to the dione. [Pg.66]

These silyl enol ethers are probably the best way of carrying out crossed aldol reactions with an aldehyde as the enol partner. An example is the reaction of the enol of the not very enolizable iso-butyraldehyde with the very enolizable 3-phenylpropanal. Mixing the two aldehydes and adding base would of course lead to an orgy of self-condensation and cross-couplings. [Pg.707]

The low oxidation potentials of stannyl compounds gave us a clue to develop the selective cross-coupling reaction between the a-posi-tions of two carbonyl compounds. Generally, silyl enol ethers or ketene silyl acetals are employed for this purpose to prepare 1,4-di-... [Pg.57]

This vanadium method enables the cross-coupling only in combinations of silyl enol ethers having a large difference in reactivity toward radicals and in their reducing ability. To accomplish the crosscoupling reaction of two carbonyl compounds, we tried the reaction of silyl enol ethers and a-stannyl esters based on the following consideration. a-Stannyl esters (keto form) are known to be in equilibrium with the enol form such as stannyl enol ethers, but the equilibrium is mostly shifted toward the keto form. When a mixture of an a-stannyl ester such as 45 and a silyl enol ether is oxidized, it is very likely that the stannyl enol ether will be oxidized preferentially to the silyl enol ether. The cation radical of 45 apparently cleaves immediately giving an a-keto radical, which reacts with the silyl enol ether selectively because of the low concentration of the stannyl enol... [Pg.60]

Silyl enol ethers (CHj = CROSiMe3) react with cyanuryl chloride and replace only one chlorine with a carbon substituent (CH2COR R = cyclopropyl, 70 /o, R = Ph, 90 /o). Friedel-Crafts arylation <83KGS1125,92EUP497734>, the Ullmann reaction of 2-iodo-1,3,5-triazine to form 2,2 -bis-1,3,5-triazine <82NKK1425>, and a palladium-catalyzed cross-coupling reaction of 2-substituted 4,6-dichloro-... [Pg.595]

Nucleophilic displacement of chlorine, in a stepwise manner, from cyanuric chloride leads to triazines with heteroatom substituents (see Section 6.12.5.2.4) in symmetrical or unsymmetrical substitution patterns. New reactions for introduction of carbon nucleophiles are useful for the preparation of unsymmetrical 2,4,6-trisubstituted 1,3,5-triazines. The reaction of silyl enol ethers with cyanuric chloride replaces only one of the chlorine atoms and the remaining chlorines can be subjected to further nucleophilic substitution, but the ketone produced from the silyl enol ether reaction may need protection or transformation first. Palladium-catalyzed cross-coupling of 2-substituted 4,6-dichloro-l,3,5-triazine with phenylboronic acid gives 2,4-diaryl-6-substituted 1,3,5-triazines <93S33>. Cyanuric fluoride can be used in a similar manner to cyanuric chloride but has the added advantage of the reactions with aromatic amines, which react as carbon nucleophiles. New 2,4,6-trisubstituted 1,3,5-triazines are therefore available with aryl or heteroaryl and fluoro substituents (see Section 6.12.5.2.4). [Pg.628]

Lewis acid promoted reactions of silicon enolates, /.e., silyl enol ethers and ketene silyl acetals with various electrophiles have yielded a wealth of novel and selective synthetic methods. This combination of reagents has been used in the past to perform such reactions as aldol-condensations with aldehydes and acetals, imine-condensations, conjugate additions to a,P-enones, alkylations, electrophilic aminations, and Diels-Alder/cyclocondensations. Our own interest in this field has involved the use of titanium tetrachloride to promote the reaction of ketene silyl acetals with non-activated imines as an efficient route to P-lactams. This reaction has been applied to the asymmetric synthesis of P-lactams via a chiral imine-titanium tetrachloride template. We have also found that both ketene silyl acetals and vinylketene silyl acetals oxidativelly dimerize or cross-couple, in the presence of titanium tetrachloride to conveniently yield various diesters . Our present study concerns reactions of vinylketene silyl acetals with non-activated imines and vinylimines promoted by titanium and zirconium tetrachlorides. [Pg.37]

In the total synthesis of (+)-lycopladine A by Toste et al. [30], a gold-catalyzed 5-endo cyclization of an iodoalkyne with a silyl enol ether has been used (Scheme 16.25). This transformation efficiently produces a -unsaturated bicyclic ketone that possesses the required quaternary asymmetric center at the position a to the carbonyl group. The vinyl iodide functionaiity generated during the cyclization was subsequently used in a palladium-catalyzed cross-coupling reaction in order to construct the pyridine ring of (-F)-lycopladine A. [Pg.221]

In 1979 Wenkert reported the cross-coupling reaction of alkenyl methyl ethers with phenyl and methyl magnesium halides via the activation of C(sp )-OMe bonds by using NiCl2(PPh3)2 as a catalyst precursor [Eq. (2)] [12, 13]. This alkenyl ether cross-coupling was further extended to silyl enol ethers [14] and cyclic ethers, such as dUiydrofurans [15-23], which offer a unique method for the stereoselective construction of alkenes (see Sect. 4). [Pg.38]

Scheme 2.59 Oxovanadium-induced oxidative cross-coupling reaction of silyl enol ethers 69 with silyl ketene aceteils 73... Scheme 2.59 Oxovanadium-induced oxidative cross-coupling reaction of silyl enol ethers 69 with silyl ketene aceteils 73...
Desilylative coupling of cinnamyltrimethylsilane results in 3,6-diphenyl-1,5-hexadiene as shown in Scheme 2.60. The cross-coupling reaction of silyl enol ethers and allylic silanes proceeds chemoselectively to give Y,8-unsaturated ketones, in which the oxovanadium(V) oxidatively desilylates the more readily oxidizable organosilicon compound [126], Their redox potentials determine whether they will act as a radical generator or acceptor. These redox potentials can be predicted from calculated ionization potentials. VO(OR)Cl2 is a versatile oxidant, which can induce chemoselective coupling via the oxidative desilylation of a variety of organosilicon compounds under controlled conditions, as shown in Scheme 2.61. [Pg.30]

Whereas the vinyl groups of Da are accessible for functionalization by hydroboration or hydrosilylation, they are inert to functionalization by cross-metathesis. Alternatively, formal metathesis products can be obtained by the ruthenium-catalyzed silylative coupling reaction. This method involves the combination of a vinyl silane and an olefin in the presence of a ruthenium catalyst, to provide an alkenylsilane (see eq 7). The application of this reaction to Da provides substitution at each of the four vinyl groups, resulting in a cyclic tetraalkenyltetramethylcyclote-trasiloxane. The silylative coupling reaction of both Da and has been demonstrated with styrenes and enol ethers. ... [Pg.485]


See other pages where Silyl enol ethers cross-coupling reactions is mentioned: [Pg.479]    [Pg.83]    [Pg.260]    [Pg.86]    [Pg.1224]    [Pg.131]    [Pg.372]    [Pg.73]    [Pg.23]    [Pg.20]    [Pg.153]    [Pg.653]    [Pg.654]    [Pg.125]    [Pg.22]    [Pg.5]    [Pg.307]    [Pg.597]    [Pg.209]    [Pg.86]   


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Coupling silylative couplings

Crossed enolate

Enolates coupling

Enolates silylation

Enolates, silyl reactions

Ethers coupling

Silyl enol ethers

Silyl enol ethers coupling reactions

Silyl enol ethers reaction

Silyl enolate

Silyl enolates

Silyl ethers reactions

Silylation reactions

Silylative coupling

Silylative coupling reactions

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