The [2+2] cycloaddition of norbornadienes and alkynes usually favours the formation of the exo adducts. Now, a nickel-catalysed endo-selective [2+2] cycloaddition has been developed, which has been used to generate otherwise elusive endo-tricyclononadienes, and further derivatized via intramolecular [2+2] photocycloaddition to synthesize homocubanes.