Synthesis of Cyclobutenes and Allenes by Cobalt-Catalyzed Cross-Dimerization of Simple Alkenes with 1,3-Enynes

Cobalt-catalyzed cross-dimerization of simple alkenes with 1,3-enynes is reported. A [2+2] cycloaddition reaction occurred, with alkenes bearing no allylic hydrogen, by reductive elimination of a (3)-butadienyl cobaltacycle. On the other hand, aliphatic alkenes underwent 1,4-hydroallylation by means of exo-cyclic -H elimination. These reactions can provide cyclobutenes and allenes that were previously difficult to access, from simple substrates in a highly chemo- and regioselective manner.