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Chiral lithium amides amine groups

Stoddart and coworkers40 have synthesized a chiral lithium amide with C2-symmetry and two chelating methoxy groups from the amine (R,R)-di(a-methoxymethylbenzyl)amine (7). This lithium amide was crystallized from a hexane solution and X-ray analysis revealed a dimeric structure where both lithiums are tetracoordinated, (Li-7)2. [Pg.388]

C. Mixed Complexes between Alkyllithiums and Chiral Lithium Amides with Chelating Amine Groups... [Pg.395]

Interligand asymmetric induction. Group-selective reactions are ones in which heterotopic ligands (as opposed to heterotopic faces) are distinguished. Recall from the discussion at the beginning of this chapter that secondary amines form complexes with lithium enolates (pp 76-77) and that lithium amides form complexes with carbonyl compounds (Section 3.1.1). So if the ligands on a carbonyl are enantiotopic, they become diastereotopic on complexation with chiral lithium amides. Thus, deprotonation of certain ketones can be rendered enantioselective by using a chiral lithium amide base [122], as shown in Scheme 3.23 for the deprotonation of cyclohexanones [123-128]. 2,6-Dimethyl cyclohexanone (Scheme 3.23a) is meso, whereas 4-tertbutylcyclohexanone (Scheme 3.23b) has no stereocenters. Nevertheless, the enolates of these ketones are chiral. Alkylation of the enolates affords nonracemic products and O-silylation affords a chiral enol ether which can... [Pg.98]

To date, several dozens of chiral lithium amide bases have been applied for enantioselective enolate formation. A collection including only several of these bases (72, 74-78) is given in Scheme 2.21. The Overberger amine [76], introduced under its lithiated form 72a by Simpkins group, still seems to be the most widely applied for this type of enantioselective bond disconnection. [Pg.38]

Conjugate addition of the lithium salt of a chiral amine to a -substituted a, 3-unsaturated ester leads to formation of a chiral, nonracemic amino acid. Addition of the chiral, nonracemic lithium amide 5.143 (contains a phenethyl auxiliary) to 5.142 gave the amino-ester.63 Catalytic hydrogenation removed both benzylic groups (the auxiliary and the benzyl group) and acid hydrolysis of the ester moiety led to 3-amino-3-(4-benzyloxyphenyl)-propanoic acid, 5.144. The initial Michael adduct was formed with >99% dr (dr is diastereomeric ratio), leading to high enantioselectivity in 5.144 after removal of the auxiliary. [Pg.166]

Davies pioneered a versatile method to prepare chiral /S-amino ester derivatives through diastereoselective conjugate additions of chiral amines onto unsaturated esters [33, 101]. Conjugate addition of lithium amide 103 to acceptor 102 thus afforded an adduct in 82 % yield, and after hydrogenolytic cleavage of the N-benzyl group this provided -amino ester 104 in >98% ee [102]. Such asymmetric amide additions have been demonstrated to have wide substrate scope with respect to the substituents that may be employed on the a,y5-unsaturated esters [33]. [Pg.400]

A number of other types of chiral auxiliaries have been employed in enolate alkylation. Excellent results are obtained using amides of pseudoephedrine. Alkylation occurs anti to the a-oxybenzyl group.93 The reactions involve the Z-enolate and there is likely bridging between the two lithium cations, perhaps by di-(isopropyl)amine.94... [Pg.42]

The Merck group has applied the electrophilic amination using lithium terf-butyl N-(tosyloxy)carbamate 9a to the chiral amide derived from (lS,2/ )-cw-amino-indanol [10] (Scheme 4). Treatment of 10 with n-Buli in THF at -78 °C gave the lithium enolate which was reacted with CuCN. The resulting amide cuprate was allowed to react with 9a. The authors found that a single diastereomer of a-Boc-protected amino amide 11 was formed. The sense of asymmetric induction observed was consistent with preferential approach of 9a from the least hindered face of the enolate. The removal of the chiral auxiliary with refluxing 6N HC1 afforded a-amino acids 12 in good yields and optical purities. [Pg.68]

Finally, a chiral triamine 35, derived from (-)-proline, has been used as the lithium salt for the deprotonation of amines (Section D.2.I.). It is obtained from A-benzyloxycarbonylproline by forming the amide with, .Ar,A -trimethyl-l,2-ethanediamine, cleavage of the protecting group, and lithium aluminum hydride reduction29. [Pg.14]

Whitesell observed that alkylation at the a-carbon of an amide of a C2-symmetric amine, in which the amine acts as a chiral auxiliary, should result in effective symmetric induction [166]. The C2-symmetric aziridines 519 and 520 are readily accessible from 503 and 514, respectively. Ring opening of either epoxide with sodium azide, mesyl activation of the free hy oxy group, and lithium aluminum hydride reduction of the azide with concomitant ring... [Pg.397]


See other pages where Chiral lithium amides amine groups is mentioned: [Pg.589]    [Pg.80]    [Pg.387]    [Pg.388]    [Pg.460]    [Pg.86]    [Pg.257]    [Pg.199]    [Pg.46]    [Pg.600]    [Pg.70]    [Pg.80]    [Pg.646]    [Pg.1047]    [Pg.178]    [Pg.646]    [Pg.52]    [Pg.279]    [Pg.497]    [Pg.1217]    [Pg.930]    [Pg.491]    [Pg.39]    [Pg.182]    [Pg.192]    [Pg.219]    [Pg.14]    [Pg.378]    [Pg.930]   
See also in sourсe #XX -- [ Pg.385 , Pg.386 , Pg.387 , Pg.395 ]




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Amide groups

Amides Chirality

Amides amines

Amination/amidation

Amination/amidation Amines

Amine groups

Amine lithium amide

Amines chirality

Chiral aminals

Chiral amines

Chiral group

Chiral lithium amides amide-amine

Lithium amide

Lithium amines

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