Nickel complex, glycine-derived

A major breakthrough in the use of Nobin as an asymmetric phase-transfer catalyst came when Belokon and coworkers applied it to the alkylation of glycine-derived nickel(II) complex 11a under the conditions shown in Scheme 8.13 [25], Representative results are given in Table 8.1, which illustrate that benzylic and allylic halides react very rapidly and highly enantioselectively to produce a-amino acids. Intrigu-ingly, in this case (R)-Nobin catalyzes the formation of (R)-amino acids, which is the opposite enantioselectivity to that observed for the alkylation of alanine derivative 16b [21,24],... 

Belokon and co-workers designed a glycine-derived nickel complex 60 and examined its asymmetric addition to methyl acrylate under phase-transfer conditions. The screening of various NOBIN and iso-NOBIN derivatives in combination with NaH as a base revealed that N-pivaloyl-iso-NOBIN (62b) proved to be highly efficient catalyst, affording the product 61 in 80% yield with 96% ee, as illustrated in Scheme 4.20 [59]. 

Diastereoselective preparation of a-alkyl-a-amino acids is also possible using chiral Schiff base nickel(II) complexes of a-amino acids as Michael donors. The synthetic route to glutamic acid derivatives consists of the addition of the nickel(II) complex of the imine derived from (.S )-,V-[2-(phenylcarbonyl)phenyl]-l-benzyl-2-pyrrolidinecarboxamide and glycine to various activated olefins, i.e., 2-propenal, 3-phenyl-2-propenal and a,(f-unsaturated esters93- A... 

Fluoral has been condensed with an equivalent of chiral glycinate anion. The chirality stems from a chiral nickel complex with a chiral Schiff base derived from proline as hgand (Figure 5.17). (25, 35)-Difluorothreonine has thus been obtained with an excellent selectivity (de > 95%). This method also allows preparation of numerous fluoroalkyl and fluoroaryl analogues of threonine. Enantiopure difluorothreonine could also be prepared from ascorbic acid. ... 

Long-range C-C, C-N and N-N couplings in selectively labelled Ni(II) complexes of the Schiff base derived from (S)-iV-benzylproline(2-benzoylphenyl)am-ide and glycine have been measured by Popkov et al in CDCb solution. Their analysis provided evidence that the donation of electron density from the jt-system of the benzyl ring to the nickel orbitals takes place. 

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