Schiff base derivatives

Co(II), Ni(n), Cu(n), and Zn(II) complexes of Schiff bases derived from 4-aryl-2-aminothiazoles and salicylaldehyde have been prepared, and structure 276 (Scheme 170) was established by magnetic susceptibility measurements and by infrared, electronic, and mass spectra (512). 

Pentafluoroaniline. Pentafluoroaniline [771 -60-8] i2is been prepared from amination of hexafluoroben2ene with sodium amide inbquid ammonia or with ammonium hydroxide in ethanol (or water) at 167—180°C for 12—18 h. It is weakly basic (p = 0.28) and dissolves only in concentrated acids. Liquid crystals have been prepared from Schiff bases derived from pentafluoroaniline (230). 

A variation involves the reaction of benzylamines with glyoxal hemiacetal (168). Cyclization of the intermediate (35) with sulfuric acid produces the same isoquinoline as that obtained from the Schiff base derived from an aromatic aldehyde and aminoacetal. This method has proved especially useful for the synthesis of 1-substituted isoquinolines. 

Figure 26.7 Model vitamin Bn compounds (a) a Schiff base derivative, and (b) a cobal-oxime, in this case derived from dimethylglyoxime.

Woodward s strychnine synthesis commences with a Fischer indole synthesis using phenylhydrazine (24) and acetoveratrone (25) as starting materials (see Scheme 2). In the presence of polyphosphor-ic acid, intermediates 24 and 25 combine to afford 2-veratrylindole (23) through the reaction processes illustrated in Scheme 2. With its a position suitably masked, 2-veratrylindole (23) reacts smoothly at the ft position with the Schiff base derived from the action of dimethylamine on formaldehyde to give intermediate 22 in 92% yield. TV-Methylation of the dimethylamino substituent in 22 with methyl iodide, followed by exposure of the resultant quaternary ammonium iodide to sodium cyanide in DMF, provides nitrile 26 in an overall yield of 97%. Condensation of 2-veratryl-tryptamine (20), the product of a lithium aluminum hydride reduction of nitrile 26, with ethyl glyoxylate (21) furnishes Schiff base 19 in a yield of 92%. 

Several silver(I) complexes of the macrocyclic Schiff base derived from the [2+2] condensation of terephthalaldehyde and 3-azapentane-1,5-diamine or A,A -bis(3-aminopropyl)methylamine have been described.509,510 The reaction of 2,ll-diaza-difluoro-m-[3,3]-cyclophane with 2,6-bis (bromomethyl)pyridine lead to the 3 + 3 addition product, which gives a complex with two silver... 

Ferrocene-containing sulfur ligands have been used in complex formation with zinc. 3-Ferro-cenyl-3-mercaptopropenale and l,l -bis(3-mercaptopropenale)ferrocene (112) form stable complexes as do their Schiff base derivatives with aniline or 1,2-ethylenediamine. The Fen/Fein redox couple shows only minor metal dependence, this is attributed to tetrahedral distortion.884... 

Pyridine derivatives with additional donor functions and sterically demanding substituents have been used with the intention of producing complexes of Cd (and of other metals) with low coordination number one of these ligands is the tridentate, planar-bonding 2,6-bis[(2,6-dimethyl-phenylimino)methyl] pyridine (pydim a Schiff base derived from 2,6-pyridine dialdehyde), which with Cd(BF4)2 and thiocyanate gives a dinuclear complex [(pydim)Cd(/x-NCS-S,N)]2(BF4)2 with N-dominated coordination sphere.191 As centrosymmetric Plijc, Z= 2), the complex has an antiparallel /x-1,3 NCS double bridge with Cd—N and Cd—S bonds (224.6 pm and 255.5 pm, respectively) the Cd—N(py) bond is clearly shorter than the Cd—N(imino) bonds (225.6 pm and 245.0 pm,... 

In the process of selective synthesis of macrocyclic Schiff bases, derivatives of chiral 1,4-diamines, the H NMR spectra were taken to confirm the synthetic route without 1H signals assignment.20... 

Recently, Bafquiren and Eddine have studied hindered Schiff base derivatives of fra/ s-l,2-diaminocyclohexane23 The differences in chemical shifts found for imino carbons have indicated the presence of anti- and syn-geometric configurations. The intense NOESY effects between protons of naphthyl and alkyl units have proved the anti-configuration of the major stereoisomer. 

The ring-chain tautomerism has been also studied for di-Schiff base derivatives of C-substituted serinols [20].41... 

P NMR studies of Schiff base derivatives of pyridoxal phosphate... 

For the tin(II) complexes of the fluorinated Schiff bases derived from amino acids, [47] the 5119Sn chemical shifts in the range from -575 to 582 ppm suggested the four-coordinate square-planar geometry.111... 

The Schiff base derivatives 73 of the 3-hetaryl-substituted 4-amino-3-thiol-l,2,4-triazoles, on treatment with acetic anhydride, undergo cyclization to give the corresponding 3-substituted-5-acetyl-5,6-dihydro-6-phenyl[l,2,4]triazolo[3,4-7][l,3,4]thiadiazoles 76 (Equation 16) <1990IJB135>. Similar treatment of 4-(A-bcnzoylamino)-4,5-dihydro-l-methyl-3-mcthylthio-1 //-[ 1,2,4 triazolc-5-thione 77 leads to the [l,2,4]triazolo[3,4-4][l,3,4]thiadiazolium trifluoromethanesulfonate 78 (Equation 17) <1986LA1540>. 

Finally, it remains to be mentioned at this point that the protonation of Schiff base derivatives of p-aminoazobenzene has also been studied (Ricketts and Cho, 1961). Benzylidene-j -phenylazo-aniline [54] and its jt>-dimethylamino-derivative in mild acid solution show absorption bands at both 320 nm and 500 nm. These bands are... 

Very reeently Kureshy et al. [98] further reported non-salen chiral Schiff base derived Ti complexes as eatalysts 70, 71 (Figure 23) in the KR of meso-siiXheae oxide, cyclohexene oxide, cyelooetene oxide and cA-butene oxide with anilines. The study deliberated upon the role of several ehiral and achiral additives with these catalysts to give chiral y9-amino alcohols with high enantioselectivity ee, >99%) in excellent yield (>99%) at 0 °C in lOh. Unlike the monomerie version 72 the chiral catalyst 70 used in this study was recoverable and recyclable several times with retention of its performance (Table 10)... 

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 new series of oxovanadium(iv) complexes with Schiff bases derived from 2-aminothiophenol and substituted salicylaldehyde (40) or 2-hydroxy-naphthaldehyde has been synthesized and characterized. The ligands (40a),... 

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