Cobalt‐Catalyzed 2+2 Cycloaddition

Three's a charm, but four's not half bad either: A simple cobalt–diphosphine complex facilitates the synthesis of cyclobutene derivatives through the chemoselective transformation of strained five-membered unsaturated rings with internal alkynes (see scheme). This atom-efficient, intermolecular reaction generates polycyclic products in excellent yields and with excellent exo selectivity. dppp=1,3-bis(diphenylphosphanyl)propane.