Synthesis of 5-arylacetylenyl-1,2,4-oxadiazoles and their transformations under superelectrophilic activation conditions

Abstract

Acetylene derivatives of 1,2,4-oxadiazoles, i.e., 5-(2-arylethynyl)-3-aryl-1,2,4-oxadiazoles, have been obtained, for the first time reported, from 5-(2-arylethenyl)-3-aryl-1,2,4-oxadiazoles by their bromination at the carbon–carbon double bond followed by di-dehydrobromination with NaNH2 in liquid NH3. The reaction of the acetylenyl-1,2,4-oxadiazoles with arenes in neat triflic acid TfOH (CF3SO3H) at room temperature for 1 h resulted in the formation of E/Z-5-(2,2-diarylethenyl)-3-aryl-1,2,4-oxadiazoles as products of regioselective hydroarylation of the acetylene bond. The addition of TfOH to the acetylene bond of these oxadiazoles quantitatively resulted in E/Z-vinyl triflates. The reactions of the cationic intermediates have been studied by DFT calculations and the reaction mechanisms are discussed.

Transformations of 5‐Hydroxy‐1‐pyrrolines in Strong Brønsted Acids: Experimental and Theoretical Study of Intermediate Cationic Species

“…Based on our works on the synthesis of 5‐hydroxy‐1‐pyrrolines [16,17] and study of the features of their chemistry, [18–21] we undertook a special investigation into the transformations of 5‐hydroxy‐1‐pyrrolines under the conditions of superelectrophilic activation by Brønsted and Lewis acids. Recently, we have also shown an efficiency of structural modification of various heterocycles in superacids [22–25] …”

“…Recently, we have also shown an efficiency of structural modification of various heterocycles in superacids. [22][23][24][25] The main goal of this work was to investigate the transformations of 5-hydroxy-1-pyrrolines under the action of Brønsted superacid CF 3 SO 3 H (triflic acid, TfOH) and strong acid H 2 SO 4 or Lewis acids AlX 3 (X = Cl, Br) including reactions with aromatic nucleophiles. Apart from that, experimental (by NMR) and theoretical (by DFT calculations) study of the intermediate cations generated from 5-hydroxy-1-pyrrolines was performed.…”

Síntese, caracterização e avaliação antimicrobiana de 1,2,4-oxadiazóis derivados do ácido trans-3,4-(metilenodioxi)-cinâmico

“…Heterocyclic structures are important of constructing numerous organic molecules geared towards various applications. Furthermore, there have been significant advances in the biological applications of widely studied fivemembered heterocyclic compounds (Biernacki et al, 2020), such as oxadiazoles, thiadiazoles, triazoles, and tetrazoles (Aliabadi, 2016, Puzanov et al, 2021Vinaya, Chandrashekara & Shivaramu, 2019.…”