The electrophilic addition of Br to −endo-benzocyclobutanorbornene× 5 at À 508 led in high yield to the formation of the rearranged dibromides 6 and 7. However, high-temperature bromination of 5 in decalin at 1508 gave exclusively nonrearranged product 8 in 98% yield. From the elimination of nonrearranged product 8, −endo-bromobenzocyclobutanorbornene× 9 and −endo-benzocyclobutanorbornene× 5 were obtained. Similarly, bromination of monobromide 9 at 778 yielded the nonrearranged tribromide 12 in quantitative yield. The dehydrobromination of 12 provided the −endo 11,12-dibromobenzocyclobutanorbornene× 3 in high yield, which is a synthon for the trimerization reactions.

We have performed an investigation on the cyclotrimerisation of molecules having exo-and endo-benzotricyclo[4.2.1.0 2,5 ]nonene skeletons (3 and 4) with the aim of producing their respective cyclotrimers 2 that feature unusual geometries and electronic properties. Activation towards the cyclotrimerisation reaction was performed using the vic-bromostannyl vinyl derivatives and was accomplished under copper-mediated or palladium-catalysed reaction conditions.

The electrophilic addition of bromine to 13-anti-bromo-endo-benzocyclobutenonorbornene 7 at −50 ± 5 °C has led in high yield to the formation of the rearranged dibromides 9, 10 and 11. In addition to this, bromination of exo isomer 8 results in formation of rearranged 9 and non rearranged product 10. However, high-temperature bromination of endo 7 and exo isomer 8 at 77 °C gave only non-rearranged products. The possible role of a substituent in rearrangements is discussed in these systems.