Chemoselective Agents for Oxidizing Alcohols

TPAP (Pr4N Ru04 ) is an air-stable oxidant for primary and secondary alcohols. It is commercially available and environmentally friendly since it is used in catalytic amounts in the presence of a co-oxidant such as AT-methylmorpholine-iV-oxide (NMO). 

It is important that the H2O produced in the reaction or any H2O derived from hydrated NMO be removed with molecular sieves. Oxidations can be performed on small or large scales. For large-scale reactions it is important to moderate the reaction by slow addition of NMO while cooling. 

TPAP tolerates a wide variety of functional groups, including double bonds, enones, halides, epoxides, esters, and lactones. Protecting groups, such as MEM, trityl, silyl and benzyl ethers, THP, and acetals, are not affected. 

Mn02 is a highly chemoselective oxidant—allylic, benzylic, and propargylic alcohols are oxidized faster than saturated alcohols. The oxidation takes place under mild conditions in H2O, acetone, or CHCI3. 

The disadvantages of oxidations with manganese dioxide include the large excess of Mn02 that is typically required for complete conversion of the starting material (it 

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