Synthesis and Characterization of New 1,3,4‐Oxadiazolines Synthese und Charakterisierung neuer 1,3,4‐Oxadiazoline

Abstract

In connection with our previous research on the synthesis of azo-substituted five membered heterocycles'") we repon here the synthetic route and the spectral characteristics of 2-aryl substituted-3-acetyl-5-[4-( 1 -phenyl-3,5-dimethyl-4-pyrazoly1azo)-phenyll-1,3,4-oxadiazolines 2a-2h. 4-( 1 -Phenyl-3.5-dimethylpyrazoly1azo)-N2-(substituted benzylidene)benzohydrazides la-lhSe8), obtained from the reaction of 1 -phenyl-3,5-dimethyl-4-(4-hydrazinocarbonylphenylazo)-pyrazole (1)9' with various aldehydes, were reacted with Ac20, but no acetyl derivatives of hydrazones were formed, instead, cyclization occured and compounds 2a-2h were obtained (Scheme).The structures of compounds 2a-2h were confirmed by means of elemental analysis and spectral data. Instead of the UV absorptions of la-lh between 348-352 run, 2a-2h showed maxima between 359-367 run. The NH-absorptions of la-lh occured at about 3200 cm", whereas 2a-2h had PhCompound 1 ArCHO I no absorptions in this region. Because both the starting compounds la-lh and the cyclization products 2a-2h have carbonyl functionalities the ab sorptions of 2a-2h at 1654-1674 cm-' (compounds 2b and 2c showed an additional C=O absorption at 1769 cm-' due to the acetylation of the OH group of the aromatic ring) could not help in structure elucidation. The 5-substituted-3-acetyloxadiazoline structure was supported by the 'H-NMR spectra of 2a-2h. Signals due to -CONH-N= at about 12 ppm disappeared after cyclization. Furthermore, the Ar-CH=N-protons of la-lh which show a one proton singlet at about 8.10-8.70 ppm region were shifted to the 7.06-7.13 ppm region. Although this proton would be expected at a little bit higher field, the inductive effect of 0 and N and the phenyl ring attached to the same C-atom shift this one proton signal more downfield than expected.The molecular structure of the compounds was further elucidated by EI-MS data. Molecular ions at m/z = 566; 508: 498; 482; 509 and 507 confirmed the molecular weights of 2c-2h, respectively. M' of 2a was not detec-

Synthesis of Some Novel Azo Derivatives of 3,5‐Dimethly‐1‐(2‐hydroxyethyl)pyrazole as Potent Analgesic Agents

“…To a solution of hydrazide 1 [23] (0.005 mol) in ethanol (60 mL), isothiocyanate (0.005 mol) was added. The mixture was refluxed for 2 h and ,after cooling, the precipitate formed was recrystallized from ethanol.…”

“…The starting material 4-(4-ethoxycarbonylphenylazo)-1-(2-hydroxyethyl)-3,5-dimethylpyrazole was prepared according to the literature [23]. 4-(4-ethoxycarbonylphenylazo)-1-(2-hydroxyethyl)-3,5-dimethylpyrazole was reacted with hydrazine hydrate in ethanol to give the hydrazide compound 1 [23].…”

Regioselective synthesis and biological evaluation of some novel thiophene-containing heterocyclic scaffolds as potential chemotherapeutic agents

“…Such a downfield signal can be assigned only to the thioamide CS carbon atom, which was reported to appear at δC value greater than 169 ppm in related systems [37][38][39][40]. It is worthwhile to report here that the thione form is the stable form in which compound 8 mainly exists since its IR spectrum revealed no absorption band at around ν 2600-2550 cm -1 , which is indicative of the thiol form [35,36,[41][42][43]. In the 1 H NMR spectrum of 8, the absence of a signal due to the SH proton that would be expected to resonate in the range δH 1.6-4.0 ppm [35,37] also provided confirmatory evidence for thione formation.…”

Synthesis and elucidation of structure of hydrazones derived from N-(2,4-dimethylphenyl)-3-oxobutanamide

“…Earlier reports indicate that diazonium salts of certain aromatic amines such as sulfaguanidine 18 and sulfanilamide 19 have been coupled with compounds possessing active hydrogen.…”