Big Chemical Encyclopedia

Chemical substances, components, reactions, process design ...

Articles Figures Tables About

Chlorotrimethylsilane silyl enol ethers from

A number of a,/J-unsaUiraled acyl silanes have been prepared from silyl enol ethers of acyl silanes (Scheme 41)129. Addition of phenyl sulphenyl chloride to the silyl enol ether with subsequent elimination of chlorotrimethylsilane gives the a-(phenylthio)acyl silane. Oxidation to the sulphoxide followed by in situ elimination of benzenesulphenic... [Pg.1623]

Trapping. The enolate generated from the enone shown below reacts at oxygen with chlorotrimethylsilane in the presence of triethylamine to produce the trimethylsilyl enol ether. Silyl enol ethers are valuable intermediates for the preparation of regiode-fmed enolates (see Chapter 6). [Pg.295]

The deprotonation of conformationally locked 4-t-butylcyclohexanone became a kind of benchmark reaction to study the efficiency of appropriate chiral bases. As shown in Scheme 2.20, the enantiotopic axial hydrogen atoms in o-position of the carbonyl group can be removed selectively by the C2-symmetric lithium base R,R) or (S,S)-72a, and the enantiomeric enolates R)-73a and (S)-73a thus formed were trapped with chlorotrimethylsilane to give enantiomeric silyl enol ethers (/ )-73b and (S)-73b, respectively. It turned out that - symptomatically for the chemistry of lithium enolates - the conditions have a dramatic effect on the enantioselectivity. When internal-quench conditions were applied (i.e., chlorotrimethylsilane present in the mixture from the very beginning), R)-73 was obtained in 69% ee. The external-quench protocol (i.e., deprotonation with the lithium amide 72a first, followed by trapping with chlorotrimethylsilane) led to a collapse of enantioselectivity (29% ee). Thus, here again, the idea came up that lithium chloride that forms gradually under the internal-quench conditions influences dramatically the deprotonation mode. Consequently, the enolate formation was performed in the presence of lithium chloride (0.5 equiv.), and chlorotrimethylsilane was added thereafter. The result was an enhancement of the ee value to 83% [75]. [Pg.38]

A derivatization of zinc enolates like 418, formed in a copper-catalyzed conjugate addition, by trapping as silyl enol ethers 419 was reported by Alexakis group [209]. The addition occurred in very high enantioselectivity when mediated by phosphoramidite 417 or related ligands. Remarkably, the selectivity was distinctly lower when chlorotrimethylsilane was present from the beginning. Therefore,... [Pg.373]


See other pages where Chlorotrimethylsilane silyl enol ethers from is mentioned: [Pg.595]    [Pg.137]    [Pg.1041]    [Pg.439]    [Pg.207]    [Pg.2464]    [Pg.61]    [Pg.366]    [Pg.40]    [Pg.648]    [Pg.95]    [Pg.302]   
See also in sourсe #XX -- [ Pg.803 ]

See also in sourсe #XX -- [ Pg.803 ]




SEARCH



Chlorotrimethylsilane

Enolates from silyl enol ethers

Enolates silylation

From enol ethers

From ethers

From silyl enol ethers

From silyl ethers

Silyl enol ethers

Silyl enol ethers chlorotrimethylsilane

Silyl enolate

Silyl enolates

Silyl ethers from enolates

© 2024 chempedia.info