Reactions of 3,3,3-Trihalogeno-1-nitropropenes with Arenes in the Superacid CF₃SO₃H: Synthesis of (<i>Z</i>)‑3,3,3-Trihalogeno-1,2-diarylpropan-1-one Oximes and Study on the Reaction Mechanism

3,3,3-Trihalogeno-1-nitropropenes C­(Hal3)­CH​CH­(NO2) (Hal = F, Cl, Br) in reaction with arenes in the superacid CF3SO3H (TfOH) at room temperature in 1 h afford 3,3,3-trihalogeno-1,2-diarylpropan-1-one oximes C­(Hal3)­CH­(Ar)–​C­(Ar)​NOH (CHal3-oximes) in yields of 23–99%. Such CHal3-oximes having one ortho-substituent in the aryl ring exist as atropoisomers in solutions at room temperature. Several cationic intermediates of this reaction were studied by means of NMR and DFT calculations, which proves the detailed reaction mechanism of the formation of CHal3-oximes in TfOH. CHal3-oximes (for Hal = Cl, Br) with DBU in DMF at microwave or thermal activation are cyclized into 5-halogeno-3,4-diarylisoxazoles in yields of 37–59%. CHal3-oximes under the conditions of Beckmann rearrangement with PCl5 in benzene at room temperature in 24 h are turned at first into imidoyl chlorides (yields of 94–96%), which undergo transformation into the corresponding benzamides PhCO­NH­CHPh­(CHal3) on silica gel (yields of 46–47%).3,3,3-三卤代-1-硝基丙烯（3,3,3-Trihalogeno-1-nitropropenes），分子式为C(Hal₃)CH=CH(NO₂)（其中Hal=F、Cl、Br），在超强酸三氟甲磺酸（CF₃SO₃H，简称TfOH）中与芳烃于室温下反应1小时，可得到3,3,3-三卤代-1,2-二芳基丙-1-酮肟（C(Hal₃)CH(Ar)–C(Ar)=NOH，简称CHal₃-oximes），产率为23%~99%。此类芳环上带有一个邻位取代基的CHal₃-肟类化合物，在室温溶液中以阻转异构体（atropoisomers）形式存在。本研究通过核磁共振波谱法（NMR）与密度泛函理论（DFT）计算，对该反应的多种阳离子中间体进行了研究，验证并阐明了在TfOH体系中CHal₃-肟类化合物生成的详细反应机理。对于Hal为Cl、Br的CHal₃-肟类化合物，在1,8-二氮杂双环[5.4.0]十一碳-7-烯（DBU）存在的N,N-二甲基甲酰胺（DMF）溶剂中，经微波或热活化后可发生环化反应，生成5-卤代-3,4-二芳基异噁唑，产率为37%~59%。在五氯化磷（PCl₅）介导的贝克曼重排（Beckmann rearrangement）条件下，将CHal₃-肟类化合物于苯中室温反应24小时，首先会转化为亚胺酰氯类化合物（产率94%~96%）；此类亚胺酰氯在硅胶（silica gel）表面可进一步转化为相应的苯甲酰胺类化合物PhCONHCHPh(CHal₃)，产率为46%~47%。