Inside and outside N-bridge cavity systems: Evidence for syn- and anti-atropisomers in scaffolds containing two N-benzoyl 7-azanorbornane units

Alkene and aziridine reagents containing N-benzoyl 7-azanorbornane components have been prepared and used to construct [n] polynorbornanes in a block building protocol. The presence of syn- and anti-atropisomers involving the restricted rotation of the N-COPh bridge was established by 1H NMR spectroscopy in an NNN-[3]polynorbornane 4 (outside bridges) whereas the anti-conformer dominated in a cavity NCOCOCN-[7]isopolynorbornane 8 (inside bridges, X-ray confirmation) prepared by a dual 1,3-dipolar addition of an acute-angled norbornene 6 with a hexacyclic bis-epoxide 7.