Regioselective thionation of bicyclic piperazinediones

In order to modify and improve the reduction of bicyclic piperazinediones to yield enantiomerically pure piperazine derivatives the preparation and reduction of the corresponding thiolactams were investigated. With a reduced amount of Lawesson reagent the bicyclic piperazinediones reacted predominantly at the C-5 carbonyl moiety to provide C-5 monothiolactams.