Reductive coupling of (azulen-1-yl)carbonyl compounds by low-valent titanium; pinacol/pinacolone rearrangement versus pinacol and alkene generation

The azulen-1-yl group strongly influences the course of the TiCl4–Zn promoted McMurry coupling of 1-acetylazulene which afforded, along with the normal coupling products, pinacol 2dl and alkene 3, the pinacolone 4. The latter was likely formed via rearrangement of the pinacolate intermediate. An improved, microwave-assisted protocol was developed for this reaction that provided high yields of products in a short reaction time. The steric reaction route is consistent with the proposed mechanism.