School of Environmental Science and Engineering, Kochi University of Technology, Tosayamada Kami, Kochi, 782-8502, Japan.
Org Biomol Chem. 2011 Oct 7;9(19):6750-4. doi: 10.1039/c1ob05682d. Epub 2011 Aug 8.
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.
一种氨甲酰取代的腈氧化物在处理易得的 2-甲基-4-硝基-3-异恶唑啉-5(2H)-酮与四氢呋喃（未干燥）时生成；即使在没有任何特殊试剂和反应条件的情况下，反应也能高效进行。腈氧化物与常见的脂肪族腈或富电子芳香族腈发生 1,3-偶极环加成反应，生成 3-官能化的 1,2,4-噁二唑，这些噁二唑有望通过氨甲酰基的化学转化作为制备各种功能材料的前体。虽然传统的 1,2,4-噁二唑的制备方法涉及富电子的腈氧化物与缺电子的腈或路易斯酸活化的腈的环加成反应，但我们的方法采用富电子的腈和缺电子的腈氧化物的互补组合 - 逆电子需求 1,3-环加成。使用 B3LYP 6-31G*的 DFT 计算支持了上述的逆反应性，并且还表明由于与亲偶极腈形成氢键，氨甲酰基存在加速效应。
