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Ketones from asymmetric conjugate addition

Cinchona alkaloids can be used to effect an asymmetric synthesis of /3-selenoaryl-ketones from cyclic enones and j8-iodo-ketones are smoothly obtained from the conjugate addition of trimethylsilyl iodide to enones, followed by hydrolysis of the intermediate trimethylsilyl ether. ... [Pg.86]

This concept was extended to an asymmetric conjugate aUcynylation of enones [59]. In this case, -alkynyl ehmination from the rhodium-alkoxide complex 101 (Scheme 22), delivers not only alkynyl-rhodium species 103 but simultaneously also reveals the reacting substrate, a, -unsaturated ketones 102. Subsequent conjugate addition gives rise to -alkynylketones 105 in high yields and enantioselec-tivities. This on-demand release and generation of the alkynyl-rhodium and the enone substrate bypasses the common dimerization issues associated with the formation of alkynyl-rhodium species from terminal alkynes. [Pg.178]

Alkenylcatecholborane 11 is a good reagent for the conjugate addition and is easily obtained by the hydroboration of an alkyne with catecholborane. One-pot asymmetric synthesis of the conjugate addition product, /9-alkenyl ketone, is possible starting from an alkyne and catecholborane without isolation of the alkenylcatecholborane [12]. [Pg.59]

Oi and Inoue recently described the asymmetric rhodium-catalyzed addition of organosilanes [35]. The addition of aryl- and alkenyltriaUcoxysilanes to u,y9-unsaturated ketones takes place, in the presence of 4 mol% of a cationic rhodium catalyst generated from [Rh(COD)(MeCN)2]BF4 and (S)-B1NAP in dioxane/H20 (10 1) at 90°C, to give the corresponding conjugate addition products (Eq. 3). The enantioselectivity is comparable to that observed with the boronic acids, as the same stereochemical pathway is applicable to these reactions (compare Scheme 3.7). [Pg.70]

Asymmetric Michael additions The anions of hydrazones (2), obtained from 1 and methyl ketones, undergo conjugate addition to a,p-unsaturated esters with virtually complete 1,6-asymmetric induction to give the adducts (S,R)-3. Ozonolysis converts these products into P-substituted 8-keto esters, (R)-4, obtained in optical yields of 96-l(X)%, with recovery of the chiral auxiliary as the nitrosamine (S)-5. The overall chemical yields of 4 are 45-62%. [Pg.31]

Chiral -substituted ketones.2 Conjugate addition of (CH3)3A1 to the ketal (2) of cyclohexenone derived from (S,S)-1 followed by acetylation results in the adduct 3, which is hydrolyzed by acid to (S)-3-methylcyclohexanone (4) in 77% ee. The ketal derived from (2R,3R)-2,3-butanediol undergoes a similar conjugate addition with low asymmetric... [Pg.480]

Carbene transfer from the silver(I) complex is not only possible to ruthenium(II) to form a catalyst suitable for asymmetric olefin metathesis, but also to copper(I) [17]. This provides a catalyst suitable for copper(I) catalysed conjugate addition of alkyl- and arylzinc reagents to P-substituted cyclic enones. The products, chiral cyclic ketones, are obtained in 88-95% isolated yield and 67-83% ee. [Pg.217]


See other pages where Ketones from asymmetric conjugate addition is mentioned: [Pg.326]    [Pg.234]    [Pg.79]    [Pg.45]    [Pg.88]    [Pg.173]    [Pg.1120]    [Pg.45]    [Pg.234]    [Pg.409]    [Pg.328]    [Pg.307]    [Pg.154]    [Pg.173]    [Pg.231]    [Pg.69]    [Pg.174]    [Pg.60]    [Pg.132]    [Pg.24]    [Pg.261]    [Pg.147]    [Pg.598]    [Pg.147]    [Pg.598]    [Pg.426]    [Pg.160]    [Pg.369]    [Pg.495]    [Pg.90]    [Pg.131]    [Pg.324]    [Pg.281]    [Pg.283]    [Pg.328]    [Pg.131]    [Pg.175]    [Pg.78]    [Pg.382]    [Pg.131]    [Pg.879]    [Pg.598]   
See also in sourсe #XX -- [ Pg.55 ]




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Addition asymmetric conjugated

Addition ketones

Asymmetric addition

Asymmetric conjugate addition

Asymmetrical ketones

Conjugate ketones

Conjugated ketones

From conjugated ketones

Ketones conjugate additions

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