Schiff bases intramolecular

The heavier chalcogens are more prone towards secondary interactions than sulfur. In particular, the chemistry of tellurium has numerous examples of intramolecular coordination in derivatives such as diazenes, Schiff bases, pyridines, amines, and carbonylic compounds. The oxidation state of the chalcogen is also influential sulfur(IV) centres engender stronger interactions than sulfur(II). For example, the thiazocine derivative 15.9 displays a S N distance that is markedly longer than that in the corresponding sulfoxide 15.10 (2.97 A V5. 2.75-2.83 A, respectively). ... 

The 8-hydroxy-7-aminoquinoline-5-sulfonic acid was used to clarify the role of intramolecular hydrogen bonding on the cyclization rate of hydroxy Schiff bases in the preparation of 2-aryloxazolo[4,5-/i]quinoline-5-sulfonic acids 13. Irradiation... 

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]. 

Woodward s ingenious synthesis of chlorophyll a is based, in the first part of the synthetic approach, on a classical porphyrin synthesis using two dipyrrylmethanes for the formation of the macrotetracycle. The problem of regioselectivity in the connection of the two unsymmetric pyrrylmethane halves 1 and 2 was solved by the formation of SchifF base 3 between the two halves prior to the condensation so that the macrotetracycle formation occurred by an intramolecular reaction. 

The optically active Schiff bases containing intramolecular hydrogen bonds are of major interest because of their use as ligands for complexes employed as catalysts in enantioselective reactions or model compounds in studies of enzymatic reactions. In the studies of intramolecularly hydrogen bonded Schiff bases, the NMR spectroscopy is widely used and allows detection of the presence of proton transfer equilibrium and determination of the mole fraction of tautomers [21]. Literature gives a few names of tautomers in equilibrium. The OH-tautomer has been also known as OH-, enol- or imine-form, while NH tautomer as NH-, keto-, enamine-, or proton-transferred form. More detail information concerning the application of NMR spectroscopy for investigation of proton transfer equilibrium in Schiff bases is presented in reviews.42-44... 

Measurements of the deuterium isotope effect for unsymmetrical di-Schiff bases fully confirmed the interrelation between proton transfer equilibria in both intramolecular hydrogen bonds.46... 

Schiff bases with intramolecular charge transfer complexes such as 2,3-bis[(4-diethylamino-2-hydroxybenzylidene)amino]but-2-enedinitrile zinc (II) (BDPMB-Zn, 187) emit red fluorescence with fluorescent quantum yields up to 67%. OLEDs with a structure of ITO/TPD/ TPD BDPMB-Zn/Alq3 BDPMB-Zn/Alq3/Mg-Ag showed very bright saturated red emission with CIE (0.67, 0.32) with a luminance of 2260 cd/m2 at 20 V and a current efficiency of 0.46 cd/A (at 20 mA/cm2). In addition, the EL spectra do not change with the doping concentration in the range of 0.5—3% [229]. 

Intramolecular formation of an imino group is possible in compounds that contain properly positioned carbonyl and amino groups (primary or secondary). The equilibrium between the open-chain parent and the cyclic Schiff base product will be pH-dependent, as explained in Sect. 11.6.1. 

The enantiopure tricarbonyl(dienal)iron complex 61 suitably transfers chirality in the piperidine ring formation. Condensation to the Schiff base is followed by the intramolecular Mannich reaction catalyzed with p-TSA. The piperidine was converted to dienomycin C (62) in five additional steps <99EJOC1517>. 

The first step in one synthesis of the antipsychotic dmg clozapine (37-5) involves UUman coupling of anthranUic acid (37-1) with 2,4-dichloronitrobenzene (30-1) to give the substituted anthranilate (37-2). The carboxyl group is then converted to the A-methylpiperazinamide (37-3) via a suitably activated intermediate as, for example, the imidazohde obtained by reaction with carbonyidiimidazole (CDl). The nitro group is then reduced to amine (37-4) by means of catalytic hydrogenation. Intramolecular Schiff base formation catalyzed by toluenesulfonic acid then completes the synthesis of clozapine (37-5) [38]. 

Intramolecular addition to benzyne generated from the Schiff base of aniline and o-chlorobenzaldehyde is thought to involve addition of an amide anion to the C=N bond [163]. This mechanism indicates donor accentuation of the ortho carbon. 

Localization of the coordination bond at the N atom (198) is characteristic of the adducts of l-methyl-2-aminobenzimidazole with chelates of tri-dentate Schiff bases (205) in which the intramolecular hydrogen N-H O... 

The kinetics of hydrolysis of N-salicylidene-2-aminothiazole (119 = HL) have been studied in aqueous 5% methanol in the presence and absence of Co11, Ni, Cu11 and Zn11.408 The solvent deuterium isotope effect on the rate of spontaneous and hydroxide-catalyzed hydrolysis of the Schiff-base anion (L ) is consistent with intramolecular catalysis by the phenoxide ion. Only... 

---