Nickel-catalysed cycloaddition oligomerisation of 1,6-diynes to medium-size cyclic polyenes

Nickel complexes having a sterically demanding N,N- or N,N,N-type ligand are demonstrated to catalyse the cycloaddition oligomerisation of 1,6-heptadiynes to produce medium-size cyclic polyenes selectively with narrow molecular dispersity and minimum side reactions. The resulting cyclic polyenes exhibit non-conjugated behaviour on NMR and UV-Vis. absorption analyses. Meanwhile, regio-isomerised cyclic polyenes including trans-disubstituted alkenes, which are generated via thermal isomerisation of the cyclic polyenes at 200 degrees C, exhibit conjugated behaviour. The present oligomerisation reaction has wide functional group compatibility, enabling the production of medium-size cyclic polyenes bearing various functional groups. A plausible reaction mechanism that accounts for the narrow polydispersity is proposed.