Intercyclic [π 2+σ2+σ2]-and π2+ π2]-cycloaddition reactions in sterically fixed norbornadiene-/quadricyclane-systems

The stereoelectronic prerequisites for unusual “zipper-type” _π 2+_σ 2+_σ 2]- and _π 2+_π 2]-reaction sequences, e.g. in the still unknown C₇H₆-pentamers (1)/(2), are being studied using model compounds with systematically varied geometrical parameters. In line with expectations based on model considerations, in the 3]-series ((6), (7)) $\text{intracyclic}$, in the 5]-series ((10), (11)) $\text{inter}$cyclic processes clearly predominate.