Models That Contain Two Chiral 1,4-Dihydronicotinamide Moieties

6 Models That Contain Two Chiral 1,4-Dihydronicotinamide Moieties 

Another successful result in the field of asymmetric reduction with NAD(P)H model compounds is accomplished by bis-nicotinamides of various types. Seki et al. (1981, 1983) and Hoshide et al. (1982) reported a high degree of asymmetric induction using NAD(P)H model compounds that have two 1,4-dihydropyridine moieties within each molecule. Compounds of this type will be abbreviated as bis(NAH), in general. The idea was based on an expectation that a C symmetry 

Similar results were obtained from bis(NAH) bridged by polymethylene chains (Seki et al. 1983). The optical yields from the reduction of ethyl benzoylformate changed with the variation of the length of the carbon chain and the maximal optical yield was obtained in the reduction with the compound bridged by six methylene groups. That the optical yield depends on the structure or the length of the bridge indicates the importance of an interaction between the two 

4- dihydronicotinamide moieties. It is obvious that the interaction involves a chelation of Mg(II) by the two nuclei because the 

4- dihydronicotinamide moiety has a large affinity toward Mg(II) as mentioned above. It was ascertained that Mg(II) and bis(NAH) form a 1 1 chelate complex and that the coordination site is primarily the amide oxygen of proline amide. The importance of complexation of this kind in the induction of chirality was also supported by the dependence of the optical yield on the molar ratio of Mg(II) to bisCNAH). The optical yield increased as the relative concentration of Mg(II) increased up to a constant value when the ratio was 1 1. These results were interpreted in terms of the complexation where one of the enantiofaces of the 1,4-dihydronicotinamide ring is specifically blocked as a result of C2 symmetry to expose the pro-R or pro- 

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