Pulse radiolysis study of the reduction of 1‐phenyl‐1‐cyanonitroethylene. Cyclization leading to 5‐amino‐4‐phenylisoxazole

It is known that the electrochemical reduction of the 1‐phenyl‐1‐cyanonitroethylene leads to the formation of a cyclic compound, the 5‐amino‐4‐phenyl isoxazole, but the mechanism of such a cyclization, which is p H dependent, is not clearly established. Pulse radiolytic methods were used to follow the various stages resulting from the reduction of the 1‐phenyl‐l‐cyanonitroethylene by the radical anion COO − in order to obtain a better understanding of the preceding reduction. The transient spectra are studied between 250 and 400 nm for times ranging from 4 microseconds to several minutes after the pulse; one of these spectra concerns the ene hydroxylamine. As expected, the changes and evolution of the spectra are p H dependent and corresponding mechanisms are proposed to explain the cyclization following the formation of the ene hydroxylamine. A general scheme is given taking into account all the results obtained.