Regioselective solvent-dependent benzannulation of conjugated enynes.

The transformation of enynes under cobalt-catalysis leads to symmetrical benzannulation products in dichloromethane. In tetrahydrofuran the cobalt-catalysed reactions afforded the unprecedented unsymmetrical benzannulation products in moderate to good yields and good regioselectivities. In addition, cyclotrimerisation of the alkyne subunit can be realised when electron-deficient enynes are applied in the cobalt-catalysed transformations to generate 1,2,4-trivinylbenzene derivatives using tetrahydrofuran as solvent.