Fig. 6. Rearrangement reactions of BCBs to give fused and spirocyclic compounds.

A Divergent Rh(I)-catalysed cycloisomerisation reactions of bicyclobutanes to give fused bicyclic structures. The selectivity of the reaction can be controlled by the choice of ligand and the initial step of the reaction involves the insertion of the rhodium into the bicyclobutane. B Reactions of bicyclobutanes that lead to spirocyclic compounds. Both a thermal Alder-Ene reaction and an acid-catalysed Semipinacol rearrangement are highlighted. Yields in brackets refer to yields determined by ¹H NMR. dppe 1,2-bis(diphenylphosphino)ethane, Ts toluene sulfonyl, Ms methane sulfonyl, PMP para-methoxyphenyl.