Synthesis of 3,5-Disubstituted 1,2,4-Oxadiazoles from Amidoximes and Aldehydes in the Superbasic System NaOH/DMSO
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hesis of 3,5-Disubstituted 1,2,4-Oxadiazoles from Amidoximes and Aldehydes in the Superbasic System NaOH/DMSO A. A. Shetneva,*, V. E. Pankratievab, A. S. Kunichkinab, A. S. Vlasova, I. K. Proskurinab, A. D. Kotovb, and M. K. Korsakova a
Dorogov Pharmaceutical Technology Transfer Center, Ushinsky Yaroslavl State Pedagogical University, Yaroslavl, 150000 Russia b
Ushinsky Yaroslavl State Pedagogical University, Yaroslavl, 150000 Russia *e-mail: [email protected] Received March 10, 2020; revised April 22, 2020; accepted April 22, 2020
Abstract—A new procedure has been proposed for the synthesis of 3,5-disubstituted 1,2,4-oxadiazoles by reaction of amidoximes with aldehydes in the superbasic system NaOH/DMSO at room temperature. The scope of the proposed procedure has been demonstrated by 15 syntheses from various amidoximes and aromatic aldehydes with 27–76% yields. The procedure is inapplicable to aliphatic aldehydes. Keywords: aldehyde, amidoxime, oxadiazole, superbasic medium, condensation, dimethyl sulfoxide, sodium hydroxide
DOI: 10.1134/S107042802007009X 1,2,4-Oxadiazoles possess various useful properties, and they occupy an important place in applied chemistry. Derivatives of 1,2,4-oxadiazoles are components of many drugs [1–4] and are used as base structures of liquid crystals, energetic compounds [5], and luminophores [6]. Several methods of synthesis of 1,2,4-oxadiazoles have been reported [7–12], the most practical of which are those based on the condensation of amidoximes with carboxylic acids and their derivatives. Superbase-catalyzed reactions of amidoximes with electrophiles, in particular with acetylene [13, 14], were studied in [15–20], where 1,2,4-oxadiazoles were synthesized from esters, imidazolides, carboxylic acid anhydrides, and other carbonyl compounds in the system NaOH/DMSO. The products of these reactions were often found to possess valuable biological properties [21–25]. However, until recently, reactions of amidoximes with aldehydes have been reported in a few publications; these reactions were catalyzed by 4-toluenesulfonic [26] or acetic acid or carried out under microwave irradiation [27], and the yields were generally moderate to low. In our opinion, the lack of reliable methods of synthesis of needed heterocyclic systems of the 1,2,4-oxadiazole series using aldehydes
as initial compounds is a serious gap in the set of tools of modern organic chemistry since aromatic and aliphatic aldehydes are synthetic precursors of carboxylic acids and their derivatives. In some cases, the use of aldehydes for the synthesis of practically important 1,2,4-oxadiazoles could be preferable from the economic viewpoint. An example is the large-scale production of such aldehydes as 4-hydroxymethylfurfural, furfural, fructose, formaldehyde, propanal, acetaldehyde, vanillin, and many others from natural raw materials. Cesium carbonate-catalyzed thermal oxidative condensation of aldehydes and amidoximes [28] has become an important step in filling the above gap in the synthesis of 1,2,4-oxadiazoles. In thi
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