Accelerating Ligands for Osmium Tetraoxide Catalyzed Racemic Dihydroxylation of α-Pinene

Abstract

Osmium tetraoxide catalyzed racemic cis-dihydroxylation of α-pinene usinf N-oxide as cooxidant and hexamethylenetetraamine as accelerating ligand in tert-butyl alcohol gives excellent yield of α-pinanediol.

Notes

In the osmium tetraoxide catalyzed TMO oxidation of cyclohexene, the rate is decreased by tert-amine ligands.^11,12 An explanation for the ligand-accelerated or-decelerated osmium tetraoxide catalyzed oxidation of alkenes depending on the oxidation mechanisms of unhindred and sterically hindered alkenes has been given.^2e,11

Osmium tetraoxide puchased in 500 mg ampules was used. To perapare 4% aqueous solution, one ampul is broken open and the two halves are dropped into a brown bottle containing 12.5 mL of water. The bottle is capped with a rubber septum and following complete dissolution of osmium tetraoxide, it is purged with a stream of nitrogen quickly. Each mililiter of this stock solution contains 0.040 g (0.157 mmol) of osmium tetraoxide.

The progress of the reaction was monitored by GC on a SE-30 column at 110°C. To obtain optimum results, one should follow the reaction by GC since longer heating of the reaction mixture reduces the yield and produces α-hydroxyketone.