Hypervalent Iodine(III)-Mediated Cyclization of Unsaturated N-Alkoxyureas: Cationic Oxybromination vs. Radical Aminobromination and Aminooxyamination

In this study we describe the reactivity of unsaturated N-alkoxyureas in the presence of different combinations of a hypervalent iodine(III) reagent and a bromide source or TEMPO. Three complementary cyclizations can be achieved depending on the reaction conditions. On the one hand, PIFA with pyridinium bromide leads to an oxybromination reaction. On the other hand, bis(tert-butylcarbonyloxy)iodobenzene with tetrabutylammonium bromide or TEMPO triggers aminobromination or aminooxyamination reactions, respectively. Control experiments showed that while the first process is ionic, the other two follow a radical manifold.