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.</p

Incorporation of a molecular hinge into molecular tweezers by using tandem cycloadditions onto 5,6-dimethylenenorbornene

Site-selective 1,3-dipolar coupling at the norbornene p-bond of 5,6-dimethylenenorbornene 1 yields cycloadducts with an end-fused 1,3-diene system which have been reacted with N=N (or C=C) dienophiles to produce ribbon molecules, in which the internal diazacyclohexene (or cyclohexene) subunits are capable of acting as conformational hinges. Direct coupling of 5,6-dimethylenenorbornene with 1,3,4-oxadiazoles or dual coupling with bis(cyclobutene epoxides) afforded bis(1,3-dienes) that diastereoselectively react with dienophiles to produce new, conformationally mobile, molecular tweezers.</p