Synthesis of some new anils: part 1. Reaction of 2-hydroxy-benzaldehyde and 2-hydroxynaphthaldehyde with 2-aminopyridene and 2-aminopyrazine.
New Schiff bases derived from 2-aminopyridene and 2-aminopyrazine have been synthesized. The UV-Visible spectra of the compounds have been investigated in acetonitrile and toluene. The compounds were in tautomeric equilibrium (enol-imine O- H...N, keto-amine O...H-N forms) in polar and nonpolar solvents. For some derivatives the keto-amine form was observed in both toluene and acetonitrile. 1H-NMR and IR results showed that all Schiff bases studied favor the enol-imine form over the keto form in a weakly polar solvent such as deuterochloroform.
Studies of chelation. Part 9. Cobalt complexes of 1-[(substituted phenyl)azo]-2-naphthol and 1-[(substituted phenylimino)methyl]-2-naphthol ligands. Tautomerism and reactivity
Spectroscopic characterisation (1H and 13C n.m.r., i.r., Raman, and u.v.–visible) of various 1-[(substituted phenyl)-azo]-2-naphthols, R-Haz (R = 4′-Me, 4′-OMe, 4′-Cl, H, 2′-OMe, 2′-Me, 2′-Cl, and 2′-Br), and 1-[(substituted phenylimino) methyl]-2-naphthols, R-Hsb (R = 4′-OMe, 4′-Me, 4′-Cl, H, 4′-Br, 4′-CF3, 4′-CN, 4′-NO2, 2′-OMe, 2′-Me, 2′-CHMe2, 2′-Cl, 2′-CN, and 2′-NO2), in the solid state and in solution in both polar and non-polar solvents has shown that the hydrogen-bonded keto-tautomer is dominant in polar solvents. Reaction of cobalt(II) salts with R-Haz and with R-Hsb in ethanol produces [CoL2], cis-[Co(HL)2X2], and fac-[CoL3](L = R-az or R-sb). The tautomeric form of the ligand in these complexes is established by vibrational spectroscopy and shown to be predominantly keto (hydrazone, ketoenamine) in [Co(R-az)2], in [Co(R-Haz)2X2], and [Co(R-Hsb)2X2]( X = Cl or Br) but predominantly enolimine in [Co(R-sb)2]. The interconversion of [CoL2] and [Co(HL)2X2] is established generally: the intermediate, five-co-ordinate [Co(R-Hsb)(R-sb)X] is identified in certain cases (R = 4-OMe, 4′-Me, or H). In the chelation process, proton loss follows ring closure and is succeeded by tautomerisation where this occurs. The facility with which the chelating ligand deviates from coplanarity of the benzene and naphthalene rings is a critical feature of the chelation process. The formation of [Co(R-az)3] from [Co(R-az)2] and from [Co(R-Haz)2X2] in the presence of air occurs easily and is acid catalysed. [Co(R-sb)3] is formed only under vigorously oxidising conditions. The isoelectronic ligands R-Haz and R-Hsb should not be regarded as identical in their reactivity towards cobalt(II).
Synthesis of 2,4-dideoxy-.beta.-D-erythro-hexopyranosyl nucleosides
The synthesis of 1-(2,4-dideoxy-β-D-erythro-hexopyranosyl)thymine (12) 1 was accomplished using two different synthetic routes. It was obtained starting either from 1,2:5,6-di-O-isopropylidene-α-D-glucofuranose or from tri-O-acetyl-D-glucal. The other modified nucleosides, with either a cytosine, guanine, or adenine moiety, were synthesized using the second reaction scheme. Deoxygenation reactions were accomplished with the (2,4-dichlorophenoxy)thiocarbonyl derivatives generated in situ