Schiff bases monoalkylation

Monoalkylation of Schiff Bases Derived from Glycine... 

Asymmetric Monoalkylation of Glycine Ester Schiff Bases... 

The requisite aldimine Schiff base 21 can be readily prepared by the simple imine formation between glycine tert-butyl ester and p-chlorobenzaldehyde in MeOH at room temperature, with the aid of MgS04. The asymmetric monoalkylation of 21 was... 

Attention has been directed to the development of selective procedures for electrophilic alkylation of 5-alkylte-trazole derivatives with an active methylene group in the a-position at C-5. Alkylation of Schiff base 340 was effected by treating an equimolar mixture of compound 340 and an alkyl halide in THF with 1 equiv of NaHMDS (—78 °C to room temperature). The highly versatile nature of this procedure allowed a facile synthesis of monoalkylated products 341 with alkyl, allyl, and benzyl halides in good yields (Equation 61) <1998TL3367>. 

Monoalkylation of Clycinate Schiff Base Asymmetric Synthesis of a-Amino Acids... 

Mn111 monoalkyls [MnR(N202)H20] where (N202) is a Schiff base ligand (161), which is analogous to the well-characterized Co111 species. Six compounds were described, all with magnetic moments near 5.0 BM. 

The starting materials are readily available by dialkylation of benzyl-amine or by the monoalkylation of alkylbenzylamines, which in turn are prepared by the reduction of Schiff bases (method 429). The method has been extended to the formation of hydroxy amines, amino esters, and amino acids. ... 

In 1978, O Donnell and coworkers developed the benzophenone imines of glycine alkyl esters 4 as glycine anion equivalents, which have been found to be perfed to use in the phase-transfer catalysis [10]. An essential feature of this reaction system lies in the selective mono substitution of the starting Schiff base, the O Donnell substrate 4. This can be possible because of the significant difference in acidity of a-hydrogen between starting substrate 4 p/C,(DMSO) 18.7 (R=Et)] and a-monosubstituted produd S p/C,(DMSO) 22.8 (R=Et, E = Me), 23.2 (R=Et, E = CH2Ph)] [11]. This dramatic acidity difference makes it possible for selective formation of only monoalkylated product without concomitant production of undesired dialkylated produd or racemization. 

O Donnell reported the asymmetric alkylation of the Schiff base of tert-h xty glycinate using TV-benzylcinchonium chloride (Scheme 3.26b, [151]). This process, which works for methyl, primary alkyl, allyl, and benzyl halides (Table 3.11), is noteworthy because the substrate is acyclic and because monoalkylation is achieved without racemization under the reaction conditions. The observed chirality sense may be rationalized by assuming an jE fO)-enolate and Jt-stacking of the benzophenone rings of the enolate above the quinoline ring on the catalyst, and approach of the electrophile as before. 

The sequence can proceed in a two- or in a one-step process. The first strategy affords clean monoalkylation of the bound primary amines. To help the formation of the intermediate Schiff base, catalytic amounts of acids or dehydrating agents can be added to the reaction mixture. The reduction of the imine is then easily achieved by treatment with, for instance, L1BH4 or NaBH(OAc)3NaBH4. 

Covalent immobilization of CRL onto an epoxy-activated macroscopic carrier leads to selective monoalkylation of the lysine amino residues which are involved in the deactivation reaction with retention of the positive charge. In contrast to the native enzyme, the immobilized enzyme is inert towards the formation of Schiff bases, which results not only in a greatly stabilized activity but also in a significant enhancement in selectivity [158]. The addition of a molecular sieve to the medium in order to trap acetaldehyde seems to have some benefit [159,160]. Alternatively, the lipase may be stabilized by adsorption onto Celite [161]. 

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