Studies on the Regioselective Rearrangement of Azanorbornanic Aminyl Radicals into 2,8-Diazabicyclo[3.2.1]oct-2-ene Systems

Aminyl radicals are nitrogen-centered radicals of interest in synthetic strategies involving C–N bond formation due to their high reactivity. These intermediate radicals are generated by the reaction of an organic azide with tributyltin hydride (Bu3SnH) in the presence of substoichiometric amounts of azobisisobutyronitrile (AIBN). In this work, we report the regioselective rearrangement of azanorbornanic ([2.2.1]azabicyclic) aminyl radicals into 2,8-diazabicyclo[3.2.1]oct-2-ene systems. With the aim to establish the structural requirements for this ring expansion, we have studied the effect of different bridgehead atoms of the [2.2.1]bicyclic system and the presence of an alkyl substituent at C4. Attempts to perform this ring expansion on a monocyclic analogue have been also explored to evaluate the influence of the bicyclic skeleton on the rearrangement. A detailed mechanistic proposal supported by computational studies is reported.