Schiffbases reduction

Schiffbase formation followed, by reduction a cis-trans isomerization is necessary to suitably position the amine and aldehyde groups... 

Figure 5-7. Affinity labelling of nucleotide bind- hyde analogue. These groups react with accessible ing proteins. Nucleotides bound to protein are lysine residues in the region ofthe nucleotide bind-treated with periodate, which cleaves the vicinal ing site to form a Schiffbase adduct this can be diol groups to generate a highly reactive dialde- stabilised by reduction with NaHB4.

Hydroamination reactions involving alkynes and enantiomerically pure chiral amines can produce novel chiral amine moieties after single pot reduction of the Schiffbase intermediate 82 (Scheme 11.27) [123]. Unfortunately, partial racemiza tion ofthe amine stereocenter was observed with many titanium based hydroamina tion catalysts, even in the absence of an alkyne substrate. No racemization was observed when the sterically hindered Cp 2TiMe2 or the constrained geometry catalyst Me2Si(C5Me4)(tBuN)Ti(NMe2)2 was used in the catalytic reaction. Also, the addition of pyridine suppressed the racemization mostly. 

Square planar metal chelates such as MP (1), MPc (2), and Schiffbase chelates (6) reduce 02 selectively as MTAA (4) for the anodic side243,244. In Fig. 10 low molecular and polymer phthalocyanines (2), (86) (both precipitated on active carbon) are compared with Pt for the reduction of 02 (Eq. 56). According to this, polyFePc (S6) has nearly the same voltage and current density as Pt. 

The stoichiometry of the reductive half-reaction is shown in Equation (2). The initial step in this reaction, as depicted in Figure 13, involves the nucleophilic attack of the primary amine substrate at C5 of oxidized TPQ (Figures 13(a) —> 13(b)). This results in the formation of a substrate Schiffbase (Figure 13(b)). In the next step, an active site base (a conserved aspartic acid) abstracts a proton to form a carbanion species (Figure 13(c)), which quickly rearranges to form a product Schiffbase (Figure 13(d)). The product aldehyde is formed by... 

MesSiCl and Mn as reducing agent the diastereoselectivity, which is excellent, depends on the SchifFbase used [241], Stoichiometric reactions of aromatic aldehydes with chiral titanium(IV) Schiff-base compounds in the presence of various reductants afforded the chiral diols in high yields and with enantioselectivities up to 91% these transformations were rendered catalytic by the addition of TMSCl [242],... 

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