Cobalt catalysis at the crossroads: cobalt-catalyzed Alder-ene reaction versus [2 + 2] cycloaddition.

The application of bidentate phosphine ligands in cobalt-catalyzed transformations of cyclic alkenes such as cyclopentene and cycloheptene with internal alkynes led to a chemoselective Alder-ene or a [2 + 2] cycloaddition reaction depending on the electronic nature of the alkyne and the bite angle of the ligand used.