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

• Main Authors: Andrey I. Puzanov, Dmitry S. Ryabukhin, Anna S. Zalivatskaya, Dmitriy N. Zakusilo, Darya S. Mikson, Irina A. Boyarskaya, Aleksander V. Vasilyev
• Format: Article
• Language: English
• Published: Beilstein-Institut 2021-09-01
• Series: Beilstein Journal of Organic Chemistry
• Subjects: acetylene-oxadiazoles; friedel–crafts reaction; hydroarylation; superelectrophilic activation; triflic acid
• Online Access: https://doi.org/10.3762/bjoc.17.158

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.