Similarity lithium amides

Additions of a range of organolithium reagents, RLi, ArLi, NC-CH2Li, RC=CLi, and ArC=CLi, show ees of 65-98%, using a chiral lithium aminosulfide auxiliary, superior to similar lithium amides with an ether instead of a sulfide, or without either... 

Aromatic enamines were prepared by dehydroha logenation of /3-bromo-amines with strong base. While trans enamines were thus formed, one obtained mostly cis enamines from rearrangement of the corresponding allylic amines under similar reaction conditions (646). Vicinal endiamines were obtained from S-dichloroamines and lithium amides (647). 

By analogy, the acetylene aldehyde 500 gives, on addition of the chiral Li-enolate 501 [79-82], the chiral //-lactams 502 and 503 in 75% yield [80-82]. Similar (fhc-tam-forming reactions are discussed elsewhere [70, 83-88]. The ketone 504 affords, with the lithium salt of the silylated lithium amide 505, the Schiff base 506, in 74% yield (Scheme 5.27). The Schiff base 506 is also obtained in 25% yield by heating ketone 504 with (C6H5)3P=N-C6H4Me 507 in boiling toluene for 7 days... 

On this basis, information about the aggregation state and the solid state structure of lithium amides becomes available. A similar relationship is known for x( O) and the Si-O-Si angle in silicates . ... 

The catalytic system has been successfully extended to polymer-bound lithium amide co-bases of type 65 (see Table 4) which, like C—Li bases of type 63 and 64, are efficient regenerating agents of HCLA and poorly reactive toward oxiranes. For instance, the isomerization of cyclohexene oxide by 0.05 equiv of HCLA 55 in the presence of 1.45 equiv of 65 affords ( l-cyclohexenol in 92% ee (entry 15). It is of interest to note that, similarly to co-bases 63 and 64, the use of 65 leads to an increase of selectivity compared to the stoichiometric reaction at room temperature (Table 2, entry. ... 

C2H5CsCCH=CH2, b.p. 50 C/140 rranHg or 89 C/760 mmHg, njy(20 ) 1.4595, can be prepared by a similar procedure from -l,4-dichloro-2-butene (commercially available), 3 equiv. of NaNH2 and C2H5Br. The yield is ca. 70%. Starting from Z-dichlorobutene the enyne is obtained in a considerably lower yield. The aqueous work-up in the latter case is very difficult because of the presence of large amounts of amorphous by-products. Peculiarly, lithium amide and Z-dichlorobutene react much more cleanly. 

Substituted cyclohexanones, bearing a methyl, isopropyl, tert-butyl or phenyl group, give, on deprotonation with various chiral lithium amides in the presence of chlorotrimethylsilane (internal quench), the corresponding chiral enol ethers with moderate to apparently high enantioselec-tivity and in good yield (see Table 2)13,14,24> 29 36,37,55. Similar enantioselectivities are obtained with the external quench " technique when deprotonation is carried out in the presence of added lithium chloride (see Table 2, entries 5, 10, and 30)593. 

Asymmetric eliminations of mew-configurated epoxides to give chiral allyl alcohols may most successfully be achieved using the chiral lithium amides which are also successful for the asymmetric deprotonation of ketones (see previous section). Problems in interpretation of asymmetric induction are also similar to those found in deprotonation of the ketones finding the optimal chiral lithium amide and reaction parameters remains largely empirical. 

The Diels-Alder reaction is an important and widely used reaction in organic synthesis (Sauer and Sustmann, 1980), and in the chemical industry (Griffiths and Previdoli, 1993). Rate enhancement of this reaction has been achieved by the use of solvents such as water, surfactants, very high pressure, lithium amides, alkylammonium nitrate salts, and macrocyclic hosts (Sherman et ak, 1998). Diels-Alder reactions can be ran in neutral ionic liquids (such as 1-butyl-3-methylimidazolium trifluoromethanesulfo-nate, l-butyl-3-methylimidazolium hexafluorophophate, l-butyl-3-methylimidazolium tetrafluoroborate, and l-butyl-3-methylimidazolium lactate). Rate enhancements and selectivities are similar to those of reactions performed in lithium perchlorate-diethyl ether mixtures. 

S)-proline. The lithium amides of />o/> -(imino-1 -isobutylethylene) and its corresponding low-molecular-weight model compound, derived from (S)-leucine, were similarly used in order to examine the polymer effects with regard to the stereoselectivity. After acetylation, N-acetyl-a-methylphenylalanine was obtained in max. 31 % optical yield 195). 

A similar sequence was reported where the asymmetry was introduced by the reaction of weio-3-substituted glutanc anhydrides and (S)-methylbenzylamines to give diastereomeric hemiamides that could be separated by recrystallization The asymmetnc desymmetrization of certain 4-aryl substituted glutanmides has also been accomplished with high levels of selectivity (up to 97% ee) by enolization with a chiral bis-lithium amide base. The selectivity of the reaction was shown to be the result of asymmetric enolization, followed by a kinetic resolution." ... 

We describe first the structures found for uncomplexed lithium amides (i.e., those not containing added neutral Lewis bases such as THF, HMPA, or TMEDA) by X-ray crystallography, by molecular orbital calculations, and by solution methods (Section III,B). In Section III,C, the structures of lithium amide complexes are discussed similarly. 

Lateral association is not restricted to lithium amides. Lithium phosphide rings (RR PLi) will have a stereochemistry similar to (RR NLi) rings. The R,R groups perpendicular to the (PLi) ring plane will preclude stacking, but facilitate laddering. The presence of a deficiency of Lewis base (less than one per Li) already precludes the formation of... 

Non-aromatic organolithium compounds can be prepared by transmetallation of resin-bound stannanes [25] or by deprotonation of alkynes [26], triphenylmethane [27], or other resin-bound C II acidic compounds with lithium amides or similar bases (Figure 4.3). The reaction of polystyrene-bound trialkylboranes with diethylzinc yields resin-bound alkylzinc derivatives [28]. 

Several asymmetric 1,2-additions of various organolithium reagents (methyllithium, n-butyllithium, phenyllithium, lithioacetonitrile, lithium n-propylacetylide, and lithium (g) phenylacetylide) to aldehydes result in decent to excellent ee% (65-98%) when performed in the presence of a chiral lithium amido sulfide [e.g. (14)], 75 The chiral lithium amido sulfides invariably have exhibited higher levels of enantioselectivity compared to the structurally similar chiral lithium amido ethers and the chiral lithium amide without a chelating group. 

As shown in Schemes 13.30 and 13.32, LDA is commonly used as the stoichiometric base, and in the presence of DBU. Recent systematic screening of a variety of lithium amide bases confirmed the superior performance of LDA [64]. It was, however, also found that in the presence of DBU, w-BuLi can be used with similar efficiency [64]. Ahlberg et al. have found it is beneficial to replace the commonly used LDA by 2-(lithiomethyl)-l-methylimidazole (64, Scheme 13.33) [66], Under these conditions, 20 mol% of O Brien s base 60 (Schemes 13.28 and 13.33) afford 93% ee in the isomerization of cyclohexene oxide [66]. Similarly, 2-lithio-l-... 

A similar synthesis of enantiopure (l )-sulfinamides 123 from indane-derived toluenesulfonyl 1,2,3-oxathiazolidine-2-oxide 121 has been developed. This method includes chemoselective ring opening with inversion of configuration at the sulfur atom, using Grignard reagent at the first step and lithium amide in liquid ammonia in the second step (Scheme 17) <2002JA7880>. Intermediate stable and crystalline sulfinate esters 122 were isolated in >95% yield in diastereopure form. 

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