Schiff base moieties

Absorption and c.d. spectra of the complex formed between oxovanadium-(iv) and the Schiff base derived from (J )-l,2-propanediamine and two moles of acac indicate that the co-ordinated Schiff base moiety is close to planarity. The lack of spin-spin coupling between metal centres in iViV -propy-lenebis(salicyliminato)oxovanadium(iv) molecules (// = 1.78BM) has been discussed. Some seven new oxovanadium(iv) complexes with iV-(2-hydroxy-... 

The Jacobsen group introduced the term Schiff base catalyst [122] to demonstrate that the structure of this novel catalyst class originates from Schiff base ligands and incorporates a Schiff base moiety notably, this term does not indicate that these catalysts operate as bases, but their high... 

The best alkylation occurs at low temperature in the presence of 10 12 equivalents of hexamethylphosphoric triamide (HMPA). Without IIMPA, the enantiomeric excesses arc lower and the methylation is slower. Furthermore, the chiral moiety of the mixed sulfate, as well as the Schiff base moiety of the methyl glycinate, determines the outcome of the a-alkylations. 

The Bolm protocol was recently used by Ellman et al. for the enantioselective oxidation of -butyl disulfide 22 [72], Excellent result was achieved in the formation of thiosulfinate 22 (91% ee, 93% yield) by using catalyst 20 (0.25 mol %) in a 0,5 mmol scale. In spite of extensive screening of chiral Schiff bases related to catalyst 20, better enantioselectivity was not realized. Chiral thiosulfinate 22 is a convenient starting material for the preparation of r-butyl sulfi-namides and t-butyl sulfoxides. Vetter and Berkessel modified the structure of the Schiff base moiety of catalyst 20 by replacing the aryl ring with a 1,l -binaphthyl system [73]. The corresponding vanadium catalyst realized 78% ee in the oxidation of thioanisol, which was better than that attained by the Bolm catalyst (59% ee). 

M. Holderbaum, H. Durr, and E. Hadjoudis, Novel bi-photochromic systems dihydroindolizines with Schiff base moiety, JPhotochem. Photobiol. A, 58, 37-50 (1991). 

The reaction of optically active, helicene derivative 121 first with o-phenylenediamine and then with Ni(OAc)2 led to a helical polymer (Mn 7000) (122) having a unique ladder-type structure with Schiff base moieties immersed in the main chain (Figure 15) 206 -phg polymer showed red-shifted absorptions with respect to nickel salophene, the parent compound for the polymer, supporting the formation of a long conjugation system. Intense CD bands were reported for the polymer. 

The presence of the l,ll-diamino-6-oxoundecane in hydrolysates of heat-treated nylon-6 [359] thus is obviously the result of the hydrolysis of the Schiff base moiety. The absence of the corresponding oxo-structure in the hydrolysates of gelled nylon-6,6 may be indicative of an analogous decarboxylation mechanism entailing intramolecular acid amide interaction Hydrolysis of the Schiff base structure yields, as indicated, hexamethylene diamine and cyclopentanone, both of which have been found. 

Holderbaum, M., Dtirr, H., and Hadjoudis, E., Novel bi-photochromic systems dihydroindohzines with a Schiff base moiety, /. Photochem. Photobiol, A Chem., 58, 37, 1991. 

Elimination of the hydroxyaminomethyl moiety from nitro oxime 15 by treatment with a diazonium salt gave hydrazone 43 (75LA1029) (Scheme 15). The same product was obtained by coupling the diazonium salt with the compound 16. On heating in aniline, oxime 15 was transformed into Schiff base 42. Acylation of the oxime 15 with benzoyl chloride in pyridine led to a mixture of furazan 44 and dinitrile 45. 

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