Ruthenium Carbene Complexes with Imidazol-2-ylidene Ligands: Syntheses of Conduritol Derivatives Reveals Superior RCM Activity

Syntheses of conduritol A, E and F derivatives are described using galactitol, d-mannitol and d-glucitol, respectively, as the starting materials. The key steps of this approach comprise a Tebbe olefination reaction for the preparation of dienes 15, 21 and 27 followed by ring closing metathesis (RCM) for the formation of the polyhydroxylated cyclohexene rings of the targets. A comparative study shows that the latter transformation is best achieved with catalytic amounts of ruthenium carbene complex 3a bearing one PCy3 and one 2,3-dihydro-1H-imidazol-2-ylidene ligand in its coordination sphere.