Oxidation of Imines by Selenium Dioxide

Despite the current interest in selenium chemistry [1—6], oxidations by selenium dioxide remained limited to only a few classes of compounds, mainly alkenes and carbonyl compounds, in addition to some special cases [7, 8]. Selenium dioxide is the cheapest and most convenient selenium reagent, and an extension of its applications to other types of com­ pounds is therefore of considerable interest. As the oxidation of carbonyl compounds by Se02 is thought to start with the enolization of the car­ bonyl compound, we suspected that imines, which are capable of forming enamines by a similar tautomerism, might be susceptible to Se02 oxidation. A literature screening revealed only one example of Se02 oxidation of imines. In 1963, Schreiber and Ripperger reported a clean oxidation of two steroid imines by selenium dioxide and obtained iminocholestenones [9]. These authors already supposed the reaction to be general, but no further applica­ tions appeared in the literature.