Ley-Griffith Oxidation
The Ley-Griffith reaction is the oxidation of primary or secondary alcohols to aldehydes or ketones. The central catalyst is tetra propylammonium perruthenate (TPAP) which is used in combination with the co-oxidant N-methylmorpholine N-oxide (NMO).
General features:
1. TPAP is a solid and an air-stable compound soluble in a range of organic solvents. 2. The reaction is fast, and there is a danger of explosion on a multigram scale and cooling might be necessary. 3. The TON of the catalyst is c.a. 250.
General conditions:
1. Solvent: DCM; room temperature; 1–16 h; yields: 80–95%. 2. Reagents: 5mol% of TPAP, 1 equivalent of alcohol, 1.5 equivalents of NMO. 3. The presence of molecular sieves enhances the reaction rate and efficiency. 4. The work-up involves purification through silica-gel column chromatography.
Ley-Griffith Oxidation
Reaction Mechanism
1. The TPAP reagent oxidizes the alcohol. 2. The TPAP–alcohol complex (ruthenate ester) rearranges to deliver the ketone. 3. NMO reactivates the catalyst.
Example
Experimental Procedure
Tetrapropylammonium perruthenate (TPAP, 0.05 eq) and N-methylmorpholine N-oxide (NMO, 6.0 eq) were added to a stirred solution of the alcohol (0.92 mmol, 1.0 eq) in anhydrous dichloromethane (9 mL) at 23 °C. After 20 h, the reaction mixture was filtered through a pad of celite. The resulting solution was washed with saturated aqueous sodium sulfite solution (10 mL) and 5% aqueous copper sulfate solution (2 mL). The combined organic layer was dried over anhydrous sodium sulfate. The resulting filtrate was concentrated under reduced pressure to give the crude residue, which was used in the next steps without further purification.
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