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 galactit ol, D-mannitol and D-glucitol, respectively, as the starting materials. The key steps of this approach comprise a Tebbe olefination reaction for the p reparation of dienes 15, 21 and 27 followed by ring closing metathesis (RCM ) for the formation of the polyhydroxylated cyclohexene rings of the target s. A comparative study shows that the latter transformation is best achieve d with catalytic amounts of ruthenium carbene complex 3a bearing one PCy3 a nd one 2,3-dihydro-1H-imidazol-2-ylidene ligand in its coordination sphere. (C) 2000 Elsevier Science Ltd. All rights reserved.