Christian Bellec

Electrochemical reduction of nitroethylenic ketones in hydroorganic medium. Preparation of 4,5-dihydroxy-2-isoxazolines

The electrochemical reduction of compounds of the typehas been investigated in hydroorganic medium between pH 0 and 7. For 3 (R1 = R2 = R3 = C6H5), the 3,4,5-triphenylisoxazole is obtained at pH 1. 3 in neutral medium, 1 (R1 = CH3, R2 = R3 = C6H5) and 2 (R1 = C2H5, R2 = R3 = C6H5) lead to 4,5-dihydroxy-2-isoxazoline (only one of such compounds is described in the literature). The structure of these compounds has been determined by the usual spectroscopic methods (ir, nmr, mass spectrometry) and by radiocrystallography. A mechanism which accounts for the whole set of our results is proposed: it involves an intermediate α,β-nitrosoethylenic compound which cyclizes into a 4,5-dihydroxy-2-isoxazoline or gives an 1,3-diketone oxime upon reduction; this last compound cyclizes into an isoxazole.