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Alkylation glycine Schiff bases

The fate of the onium carbanion Q+R incorporated into the organic phase depends on the electrophilic reaction partner. The most studied area in the asymmetric phase-transfer catalysis is that of asymmetric alkylation of active methylene or methine compounds with alkyl halides, in an irreversible manner. The reaction mechanism illustrated above is exemplified by the asymmetric alkylation of glycine Schiff base (Scheme 1.5) [8]. [Pg.4]

In addition to the glycinate Schiff base 1, glycine amide derivatives can be used as prochiral substrates for asymmetric alkylation under phase-transfer conditions. Kumar and Ramachandran examined the benzylation of various Schiff bases of... [Pg.18]

Enantioselective Michael addition of glycine derivatives by means of chiral phase-transfer catalysis has been developed to synthesize various functionalized a-alkyl-a-amino acids. Corey utilized 4d as catalyst for asymmetric Michael addition of glycinate Schiff base 1 to a,(3-unsaturated carbonyl substrates with high enantioselectivity (Scheme 2.15) [35,36]. With methyl acrylate as an acceptor, the a-tert-butyl-y-methyl ester of (S)-glutamic acid can be produced, a functionalized glutamic acid... [Pg.22]

Diastereoselective Alkylation of Glycine Schiff Base with Optically Enriched Alkyl Halides... [Pg.87]

The vast synthetic utility of the asymmetric phase-transfer alkylation of glycine Schiff base 2 has been realized by its successful application to the synthesis of various useful amino acid derivatives and natural products. [Pg.87]

Using a IM KOH aq solution, it is possible to perform the asymmetric alkylation of the benzophenone glycine Schiff base with benzyl bromide using 10 mol% of 15 at room temperature, as shown in Figure 14. [Pg.49]

The asymmetric alkylation of glycine derivatives is one of the most simple methods by which to obtain optically active a-amino acids [31]. The enantioselective alkylation of glycine Schiff base 52 under phase-transfer catalysis (PTC) conditions and catalyzed by a quaternary cinchona alkaloid, as pioneered by O Donnell [32], allowed impressive degrees of enantioselection to be achieved using only a very simple procedure. Some examples of polymer-supported cinchona alkaloids are shown in Scheme 3.14. Polymer-supported chiral quaternary ammonium salts 48 have been easily prepared from crosslinked chloromethylated polystyrene (Merrifield resin) with an excess of cinchona alkaloid in refluxing toluene [33]. The use of these polymer-supported quaternary ammonium salts allowed high enantioselectivities (up to 90% ee) to be obtained. [Pg.82]

Nagasawa and co-workers developed the C2-symmetric chiral pentacyclic guanidine 11 as a chiral phase-transfer catalyst for the enantioselective alkylation of tert-butyl glycinate Schiff base (Equation 10.25) [53]. [Pg.320]

Table 4.6 Selected a symmetric alkylation oftert-butyl glycinate Schiff base with alkyl halides in the presence of 76... Table 4.6 Selected a symmetric alkylation oftert-butyl glycinate Schiff base with alkyl halides in the presence of 76...
Phase transfer reactions have featured in several sections of this book, including epoxidation (Section 4.5), Darzens condensation (Section 7.5) and Wadsworth-Emmons reactions (Section 12.5). Another important aspect of phase-transfer catalysed reactions has been with alkylation reactions. The asymmetric alkylation of glycinate Schiff base (12.45) using N-benzylcinchoninium halides as catalysts is particularly noteworthy, since the products are readily converted into amino acids. Corey and coworkers have developed the original work. [Pg.339]

Another synthetic approach was used by Lamaty et al. in asymmetric alkylation of Schiff bases in ball mill (Scheme 2.69) [59]. In optimized reaction conditions, grinding of Schiff base of glycine ester 213 with organic halides in the presence of... [Pg.122]

O Donnell s pioneering studies were reported, the catalytic efficiency of newly developed phase-transfer catalysts has been evaluated by the alkylation of glycine Schiff base 5 and for these catalysts the particular allqrlation studied and enantiomeric excess will be given in parentheses during the discussion of the catalyst. [Pg.86]

In 1999, we designed and prepared structurally rigid, chiral spiro ammonium salts of type 14 derived from commercially available (S)- or (R)-l,l -bi-2-naphthol as a new C 2-symmetric chiral PTC and successfully applied them to the highly efficient, catalytic enantioselective alkylation of glycine Schiff base under mild phase-transfer conditions. ... [Pg.148]

Scheme 17.23 Synthesis of a,a-dialkyl-a-amino acids by double alkylation of glycine Schiff base. Scheme 17.23 Synthesis of a,a-dialkyl-a-amino acids by double alkylation of glycine Schiff base.
SCHEME 8.1. Asymmetric alkylation of glycine Schiff base 1 using CB catalysts I-VIII. [Pg.269]

The alkylation of ambident enolates of a methyl glycinate Schiff base has been studied computationally/ Although the E- and Z-enolates have similar energy and geometry, and similar transition states with ethyl chloride, the -enolate is substantially more stabilized by lithium cation. [Pg.14]

The influence of the coordination of lithium and sodium enolates on the stereochemical outcome of their aldol reactions has been reviewed. The alkylation of the ambident enolates of a methyl glycinate Schiff base with ethyl chloride have been studied at B3LYP and MP2 levels. The transition states for the alkylation of the free ( )/(Z)-enolate with ethyl chloride have energy barriers of 13kcalmol However, with a lithium ion, the ( )-enolate behaves as an ambident enolate and makes a cyclic lithium complex in bidentate pattern, which is more stable by 11-23 kcal mor than the (Z)-enolate-lithium complexes. The results suggest that the alkylation of ambident enolates proceeds with stable cyclic bidentate complexes in the presence of metal ion and solvent. [Pg.362]

The pioneering contribution from Maruoka and coworkers [37] on the enantioselec-tive phase-transfer alkylation of Schiff bases derived from glycine has opened the way to other related, more recent MBTs. [Pg.358]

The a-alkylation of glycine Schiff base 233 has become one of the most important applications of chiral PTCs, and... [Pg.224]


See other pages where Alkylation glycine Schiff bases is mentioned: [Pg.418]    [Pg.129]    [Pg.4]    [Pg.4]    [Pg.83]    [Pg.118]    [Pg.120]    [Pg.130]    [Pg.226]    [Pg.253]    [Pg.302]    [Pg.384]    [Pg.398]    [Pg.179]    [Pg.112]    [Pg.137]    [Pg.151]    [Pg.230]    [Pg.138]    [Pg.85]    [Pg.86]    [Pg.88]    [Pg.149]    [Pg.268]    [Pg.274]    [Pg.250]    [Pg.252]    [Pg.224]   
See also in sourсe #XX -- [ Pg.9 , Pg.10 , Pg.11 , Pg.12 , Pg.13 , Pg.14 , Pg.15 , Pg.16 , Pg.17 , Pg.18 ]




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Diastereoselective Alkylation of Glycine Schiff Base with Optically Enriched Alkyl Halides

Diastereoselective alkylation, glycine Schiff bases

Glycine Schiff bases

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