Reactions of complex ligands: Part 94. Chromium-templated angular versus linear benzannulation of dibenzofuran and haptotropic metal migration in tetracyclic fused arenes

The chromium-templated [3+2+1]-benzannulation of dibenzofuryl(methoxy)carbene complex 1 with alkynes leads to hydroquinoid benzonaphthofurans. A competition of angular versus linear annulation affords angular-fused (η6-1,2,3,4,4a,11c)-benzo[b]naphtho[1,2-d]furan tricarbonyl chromium complexes 2–6 along with considerable amounts of uncoordinated benzo[b]naphtho[2,3-d]furans as linear annulation products 7–9. As demonstrated for 2 and 6 the Cr(CO)3 complexes undergo a thermally induced haptotropic metal migration along the tetracyclic heteroaromatic π-system to give (η6-7a,8,9,10,11,11a)-benzonaphthofuran complexes 10 and 11 in which the chromium fragment is coordinated to the terminal unsubstituted benzoid ring. The molecular structures of both the kinetic annulation products and the thermodynamic rearrangement products were established by NMR spectroscopy and single crystal X-ray analysis.