“…The diamine system of 2,5-diazabicyclo[2.2.1]heptane is traditionally included in screening libraries as a rigid counterpart of the flexible piperazine ring (Siebeneicher et al, 2016;Dam et al, 2016;Cernak et al, 2017;Llona-Minguez et al, 2017;Wei et al, 2017). As a consequence, numerous synthetic routes for the preparation of 2,5-diazabicyclo[2.2.1]heptane derivatives have been introduced (see: Portoghese & Mikhail, 1966;Jordis et al, 1990;Yakovlev et al, 2000;Fiorelli et al, 2005;Beinat et al, 2013;Cui et al, 2015;Choi et al, 2016 and the references cited therein). At the same time, the reported structural data on 2,5diazabicyclo[2.2.1]heptane derivatives are surprisingly scarce (see the Database survey).…”