Schiffs base nucleophile

Schiff base nucleophiles have been employed with cationic cyclohexadienylium)Fe(CO)3] complexes to gain access to intermediates that are suitable for elaboration into new amino acid structures i ... 

The nucleophilicity of amine nitrogens is also differentiated by their environments. In 2,4,5,6-tetraaminopyrimidine the most basic 3-amino group can be selectively converted to a Schiff base. It is meta to both pyrimidine nitrogens and does not form a tautomeric imine as do the ortho- and /xira-amino groups. This factor is the basis of the commercial synthesis of triamterene. 

Pd-cataly2ed reactions of butadiene are different from those catalyzed by other transition metal complexes. Unlike Ni(0) catalysts, neither the well known cyclodimerization nor cyclotrimerization to form COD or CDT[1,2] takes place with Pd(0) catalysts. Pd(0) complexes catalyze two important reactions of conjugated dienes[3,4]. The first type is linear dimerization. The most characteristic and useful reaction of butadiene catalyzed by Pd(0) is dimerization with incorporation of nucleophiles. The bis-rr-allylpalladium complex 3 is believed to be an intermediate of 1,3,7-octatriene (7j and telomers 5 and 6[5,6]. The complex 3 is the resonance form of 2,5-divinylpalladacyclopentane (1) and pallada-3,7-cyclononadiene (2) formed by the oxidative cyclization of butadiene. The second reaction characteristic of Pd is the co-cyclization of butadiene with C = 0 bonds of aldehydes[7-9] and CO jlO] and C = N bonds of Schiff bases[ll] and isocyanate[12] to form the six-membered heterocyclic compounds 9 with two vinyl groups. The cyclization is explained by the insertion of these unsaturated bonds into the complex 1 to generate 8 and its reductive elimination to give 9. 

Antidepressant activity is retained when the two carbon bridge in imipramine is replaced by a larger, more complex, function. Nucleophilic aromatic substitution on chloropyridine 31 by means of p-aminobenzophenone (32) gives the bicyclic intermediate 33. Reduction of the nitro group (34), followed by intramolecular Schiff base formation gives the required heterocyclic ring system 35. Alkylation of the anion from 35 with l-dimethylamino-3-chloropropane leads to tampramine 36 [8]. 

The first example of asymmetric catalytic ring-opening of epoxides with sp2-hybridized carbon-centered nucleophiles was reported by Oguni, who demonstrated that phenyllithium and a chiral Schiff base ligand undergo reaction to form a stable system that can be used to catalyze the enantioselective addition of phenyllithium to meso-epoxides (Scheme 7.24) [48]. Oguni proposed that phenyllithium... 

The stereocontrol observed in these reactions is rationalized on the basis of zinc complexes formed with the Schiff bases, as described in Section 1.4.4.2.2. The isocyanide, being a free and potent nucleophile, attacks this complex from the sterically less-hindered side, that is. from the side of the ring oxygen. 

The interaction of PCSs with nucleophilic reagents was studied by us we took the reactions of hydrazine and phenylhydrazine with polyazines, poly(schiff base)s, and other polymers containing conjupted C=N bonds as an example40,41, U7,258. ... 

Tanaka et al.28 have synthesised a series of (S)-chiral Schiff bases as the highly active (yield 69-99%) and enatioselective (ee 50-96%) catalysts in the reaction of addition of dialkylzinc to aldehydes. The stereochemistry of the asymmetric addition was suggested. In a transition state when S-chiral Schiff base was used as chiral source, the alkyl nucleophile attacked Re face of the activated aldehyde and formed the R-configuration alkylated product [13]. 

Figure 3.14 Carbonyl groups can react with amine nucleophiles to form reversible Schiff base intermediates. In the presence of a suitable reductant, such as sodium cyanoborohydride, the Schiff base is stabilized to a secondary amine bond.

We believe that the intermediate generated by anodic oxidation of 3 is the cation 3a and not nitrilimine 3b. The generation of the cation intermediate was postulated in several papers on the anodic oxidation of hydrazone derivatives [38-41], W also believe that both heteroaromatic and Schiff bases react with the cation 3a as nucleophiles rather than dipolarophiles. The most likely mechanism of the oxidation of the hydrazone 3 in the presence of heteroaromatic and Schiff bases, which would best fit the observed electrochemical and preparative results, can be described in the form of Scheme 8. 

The formation of bicycles 88 occurred through the iminium intermediate 89, in the similar manner as Ugi-reaction. But in contrast to the four-component classical Ugi-reaction, the protonated Schiff base 89, containing both nucleophilic and electrophilic centers, undergoes [4+1] cycloaddition with isonitrile to the bicyclic adduct 90 followed by rearomatization via 1,3-H shift (Scheme 39). 

Formation of compounds like 115 seems to have occurred in the similar way as it was established for anilines and other primary amines [167]. The initial step of this reaction is treatment of aldehyde with aminozole giving Schiff base 116. Further, nucleophilic attack of imine carbon by mercapto moiety of the acid leads to the intermediate 117 and its subsequent cyclization via gem-diol 118 yields target heterocycles 115 (Scheme 55). 

Oxime hgations can be significantly accelerated by using aniline as a nucleophilic catalyst . Rate enhancements are achieved by changing the electrophile from a weakly populated protonated carbonyl (Scheme 2a) to a more highly populated protonated aniline Schiff base (Scheme 2b). The transimination of the protonated aniline Schiff base to the oxime proceeds rapidly under aqueous acidic conditions. 

The first step of the enzymatic process is the transaldimination of the Schiff base lysine-PLP by the amino acid. The pulling out of the proton in a of the fluorinated amino acid is accompanied by elimination of a fluorine atom of the CX2F group, thus affording a very reactive quinonic species. This latter one can further react with a nucleophilic entity of the enzyme (e.g., the lysine of the active site) ( Michael addition inactivation process ) (Figure 7.47). ... 

Other nitrogen nucleophiles such as hydrazines, hydrazides, and Schiff bases have affected ring opening of oxazolones. Most often, hydrazine or substituted hydrazines are used. For example, hydrazinolysis of 525 affords the corresponding hydrazides 526 that, depending upon the substituents and the reaction conditions, can cyclize in the reaction medium to the aminoimidazolone 527 (Scheme 7.167 ... 

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