Metal-Induced Cyclization of Thiosemicarbazones Derived from β-Keto Amides and β-Keto Esters:  Open-Chain and Cyclized Ligands in Zinc(II) Complexes

Abstract

The reactions of Zn(OAc)(2) with acetoacetanilide, methyl acetoacetate, o-acetoacetanisidide, and ethyl 2-methylacetoacetate thiosemicarbazones (HTSC(1), HTSC(2), HTSC(3), and HTSC(4), respectively) were explored in methanol. With HTSC(1), HTSC(2), and HTSC(3), following isolation of the corresponding zinc(II) thiosemicarbazonates [Zn(TSC(x))(2)] (x = 1, 2, 3), the mother liquors afforded pyrazolonate complexes [ZnL(1)(2)(H(2)O)] (HL(1) = 2,5-dihydro-3-methyl-5-oxo-1H-pyrazole-1-carbothioamide) that had been formed by cyclization of the corresponding TSC(-). The reaction of HTSC(4) with zinc(II) acetate gave only the pyrazolonate complex [ZnL(2)(2)(H(2)O)] (HL(2) = 2,5-dihydro-3,4-dimethyl-5-oxo-1H-pyrazole-1-carbothioamide). All compounds were studied by IR and NMR spectroscopy, and HTSC(3), [Zn(TSC(3))(2)] x DMSO, [ZnL(1)(2)(H(2)O)] x 2DMSO, and [ZnL(2)(2)(H(2)O)] x 2DMSO were also studied by X-ray diffractometry, giving a thorough picture of the cyclization process. In preliminary tests of the effects of HL(1) and [ZnL(1)(2)(H(2)O)] on rat paw inflammatory edema induced by carrageenan, HL(1) showed antiinflammatory activity.

New Pd(II) and Pt(II) complexes with N,S-chelated pyrazolonate ligands: Molecular and supramolecular structure and preliminary study of their in vitro antitumoral activity

“…Physical and analytical properties of HTSC n and HL n have been reported elsewhere [16][17][18][19][20].…”

“…In all of these complexes, the two pyrazolonates L À formed by cyclization of the starting thiosemicarbazone are N,S-coordinated, as in other metal complexes [16][17][18][19][20], and have a more or less distorted square-planar environment around the metal. All of the complexes adopt a trans configuration apart from cis-½PtL 2 2 Á 2DMSO.…”

Metal‐Catalysed Oxidation Processes in Thiosemicarbazones: New Complexes with the Ligand N‐{2‐([4‐N‐Ethylthiosemicarbazone]methyl)phenyl}‐p‐toluenesulfonamide

“…[32,42] Based on a careful analysis of the available data, we surmise that the formation of the triazole ring could be induced by an attack of the oxidising agent on the tail-like thioamide moiety, followed by a single-electron transfer and then a rate-limiting ring-closure step. Alternatively, the thiadiazole heterocycle is formed as a result of an attack of the metal cation on the imine nitrogen atom, followed by a ringclosure step and finally an electron abstraction-dehydrogenation step.…”

Coordination modes of 5-pyrazolones: A solid-state overview

“…All these carbothioamide-5-pyrazolones were obtained by elimination-cyclization processes involving ␤-keto ester or ␤-keto amide thiosemicarbazones (H␤TSCs) in the presence of a metal cation (although other factors such as pH, temperature and the nature of the solvent may influence the process) [109][110][111][112][113][114] (see Scheme 15).…”

“…However, [ReBr(CO) 3 (HL 55 )] is a monomer [109] (Fig. 49) [110,112] have also been prepared, as was indicated in Scheme 15, by reaction of Zn(OAc) 2 and the corresponding thiosemicarbazone ligand in MeOH (at room temperature or under reflux). These complexes contain monodeprotonated N2, S-bound pyrazolonate ligands and the complexes [Zn(L n ) 2 ] have a distorted tetrahedral geometry (see Fig.…”