Oxydation d'hydrazones par le bioxyde de plomb: Nouvelles synthèses d'oxadiazoles‐1,3,4 et de dérivés de l'amino‐4 triazol‐1,2,4 one‐5

Abstract

L'oxydation des aroylhydrazones d'aldéhydes aromatiques, par le bioxyde de plomb, dans l'acide aceti‐que, constitue une nouvelle méthode d'accés, simple et rapide, aux oxadiazoles‐1,3,4 correspondants. Dans le diméthylformamide, et en presence du měme oxydant, les carbodihydrazones d'aldéhydes aromatiques con‐duisent aux aryl‐3 arylidéneamino‐4 triazol‐1,2,4 ones‐5 correspondantes. Plusieurs mécanismes radicalaires sont proposés.

Hypervalent iodine(III) mediated synthesis of novel unsymmetrical 2,5-disubstituted 1,3,4-oxadiazoles as antibacterial and antifungal agents

“…Pyrazole nucleus has pronounced pharmacological applications as anti-anxiety [14], antidiabetic [15], antimicrobial [16e18], herbicidal [19,20], antiinflammatory drugs [21] and antibacterial [22e24]. Besides the dehydration of diacylhydrazines, oxidative cyclization of aldehyde N-acylhydrazones is the most known method to prepare unsymmetrically 2,5-disubstituted 1,3,4-oxadiazoles, and several reagents have been reported to in the literature which include oxidation with ceric ammonium nitrate [25], chloramine T [26], lead tetraacetate [27,28], potassium permanganate under microwaves conditions [29], ferric chloride [30], bromine/sodium acetate [31], or yellow mercuric oxide/iodine [32]. In recent years, hypervalent iodine reagents have been successfully proven their usefulness as agents for oxidative cyclization of aldehyde N-acylhydrazones to synthesize 2,5-disubstituted 1,3,4-oxadiazoles [33e38].…”

Synthesis, oxidation and dehydrogenation of cyclic N,O‐ and N,S‐acetals. Part III. Transformation of N,O‐acetals: 3‐acyl‐1,3,4‐oxadiazolines

“…Moreover, treatment with (diacetoxyiodo)benzene in methanol at room temperature for 19 hours failed to transform oxadiazolines (2f) or 5-(2-acetoxyphenyl)-3-acetyl-2-(2,4dichlorophenyl)-1,3,4-oxadiazoline (2g) into the corresponding oxadiazoles (3f and 3g, respectively), the reaction 2g 3g, however, was complete in 2.5 hours by CAN dehydrogenation at room temperature (see Table 5). On the other hand, treatment with CAN under similar conditions degraded 2,4-dichlorobenzaldehyde N-(2acetoxybenzoyl)-N-acetylhydrazone (6d), the open-chain isomer of oxadiazoline (2g), to the parent aldehyde (4g), as well as 2,3,4,5,6-penta-O-acetyl-D-galactose diacetylhydrazone (10) to 2,3,4,5,6-penta-O-acetyl-D-galactose isolated as its ethyl hemiacetal (11,see EXPERIMENTAL).…”

“…As a valuable and versatile alternative, dehydrocyclization of aldehyde acylhydrazones has been effected by treatment with a variety of oxidants such as chlorine-carbon tetrachloride [6], potassium hexacyanoferrate(III)-aq. sodium hydroxide [7], 3methylbutylnitrite-diethyl ether [7], iodine-mercury(II) oxide [8a,b,9], lead(IV) acetate [10,12d], lead(IV) oxideacetic acid [11], nickel(II) peroxide [10e], brominesodium acetate [12a-i], iodine-aq. sodium carbonate [12j], iron(III) chloride-acetic acid [13], potassium permanganate-acetone [10d], Chloramine T [14], (diacetoxyiodo)benzene [15] which transforms also N,N'-diacylhydrazines into oxadiazoles [16], and zinc chloride-acetic acid [17].…”

An iodine-mediated green synthesis of 1,3,4-oxadiazoles under solvent-free conditions using grinding technique

“…These compounds are generally prepared by oxidative cyclization of N-acyl hydrazones prepared by the reaction of aromatic hydrazides with aromatic aldehydes. For this, various oxidizing agents have been used, including very toxic lead tetraacetate (11), lead dioxide (12), potassium permanganate (13), chloramine-T (14), HgOÁI 2 (15), ferric chloride (16), and iodobenzenediacetate (17).…”