In addition, the bidentate ligand L 1 is found to effective for the OsO4 -mediated dihydroxylation of trans -disubstituted and monosubstituted alkenes (Scheme 4). The reaction is believed to involve intermediate A and the products are obtained with high yield and enantioselectivity.
Scheme 4
5.6.1.1 Synthesis of Biologically Important Molecules
The Os-catalyzed enantioselective dihydroxylation is used as a key step in the highly expeditious synthesis of the antibacterial agent (–)-chloramphenicol (Scheme 5).
Scheme 5. Synthesis of Chloramphenicol
The synthesis of the β -receptor-blocking drug ( S ) - propranolol has been demonstrated employing osmium-catalyzed dihydroxylation as a key step (Scheme 6). Reaction of α - naphthol with allylic bromide gives allyl naphthyl ether that could be dihydroxylated using AD-mix - β with 91% ee. The diol derivative could be converted into ( S ) - propranolol by classical methods.
Scheme 6. Synthesis of (S)- Propranolol