Organic Synthesis

OsO₄ is more selective than permanganate for preparing cis-diols. However, it is also toxic and more expensive. As a comparison, 1 g (OsMO₄) $266, 25 g (KMnO₄) $43 in Aldrich and you can also purchase KMnO₄ from a store since it is also used as an antiseptic.

To overcome these limitations, NMO (N-methylmorpholine N-oxide) is added to the reaction and it deoxidizes the Os6⁺ species back into OsO₄ which can perform another oxidation of the alkene.