Through-space interaction between proximal olefins, as in norbornadiene (NBD), leads to reactivity analogous with conjugated dienes. 1 NBD reacts directly with tetracyanoethylene to give a homo-Diels−Alder [(2+2)+2] adduct. 2 In the presence of transition-metal catalysts, NBD and acetylenes generate homo-Diels−Alder products among other coupling products, depending on the catalyst. 3 Similar perturbations of reactivity could be anticipated for functional ...