Synthesis of 2,6-diazabicyclo[3.3.1]nonanes <i>via</i> intramolecular cycloaddition of nitrones

A new synthesis route to 2,6-diazabicyclo[3.3.1]nonanes as a scaffold of conformationally restricted diamines is disclosed. Starting from 4-amino-1-Boc-piperidine (Boc = <i>tert</i>-butoxycarbonyl), introduction of an alkene unit on the 4-amino group, followed by removal of the Boc group, afforded secondary amines. Subsequent oxidation of the amines with Oxone furnished nitrones, which underwent intramolecular cycloaddition to construct the 2,6-diazabicyclo[3.3.1]nonane skeleton.