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

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posted on 13.07.2018, 00:00 by Andrei A. Golushko, Maria A. Sandzhieva, Alexander Yu. Ivanov, Irina A. Boyarskaya, Olesya V. Khoroshilova, Alexey Yu. Barkov, Aleksander V. Vasilyev
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%).