Inverse electron-demand 1,3-dipolar cycloaddition of nitrile oxide with common nitriles leading to 3-functionalized 1,2,4-oxadiazoles |
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Authors: | Nishiwaki Nagatoshi Kobiro Kazuya Hirao Shotaro Sawayama Jun Saigo Kazuhiko Ise Yumiko Okajima Yoshikazu Ariga Masahiro |
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Institution: | School of Environmental Science and Engineering, Kochi University of Technology, Tosayamada Kami, Kochi, 782-8502, Japan. nishiwaki.nagatoshi@kochi-tech.ac.jp |
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Abstract: | A carbamoyl-substituted nitrile oxide was generated upon treatment of easily available 2-methyl-4-nitro-3-isoxazolin-5(2H)-one with THF (not dried); the reaction proceeded efficiently even in the absence of any special reagents and reaction conditions. The nitrile oxide caused 1,3-dipolar cycloaddition with common aliphatic nitriles or electron-rich aromatic nitriles to afford 3-functionalized 1,2,4-oxadiazoles, which are expected to serve as precursors for the preparation of a variety of functional materials by the chemical transformation of the carbamoyl group. While conventional preparative methods for 1,2,4-oxadiazoles involve the cycloaddition of an electron-rich nitrile oxide with an electron-deficient nitrile or a nitrile activated by a Lewis acid, our method employs the complementary combination of an electron-rich nitrile and an electron-deficient nitrile oxide- the inverse electron-demand 1,3-cycloaddition. The DFT calculations using B3LYP 6-31G* supported the abovementioned inverse reactivity, and also suggested the presence of an accelerating effect by the carbamoyl group as a result of hydrogen bond formation with a dipolarophilic nitrile. |
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