General Procedure for Oxidation of Alcohols with TPAP

General Procedure for Oxidation of Alcohols with TPAP 

Between 0.02 and 0.15 typically 0.05 equivalents3 of TPAP (MW = 351.43) are slowlyb added to a ca. 0.02 0.3 M solution of the alcohol in CH2C12,c containing ca. 0.2 0.7 g of 4 A molecular sieves 1 per mmol of alcohol and ca. 1.1 to 2.5—typically 1.5 equivalents of TV-methylmor-pholine /V-oxide (NMO, MW = 117.15). The resultant mixture is stirred at room temperature1 till most of the alcohol is consumed.8 This is followed by a work-up that can be carried out according to two alternative protocols  

The reaction mixture is filtered through a pad of Celite or silica gel and the resulting solution is concentrated, providing a residue that may need further purification. When the oxidation is performed in the presence of acetonitrile as solvent, as it tends to wash residual TPAP through the Celite or silica pad, it is advisable to evaporate the solvents and add some CH2C12 before the filtering. 

5% yield of the desired ketone with no epimerization at the ot-position is obtained, employing catalytic TPAP as oxidant. Other oxidizing conditions, including Collins, Sarett, Oppenauer and Swern oxidations, as well as PCC, fail to deliver an acceptable yield of 

While PCC produces an oxidative C-C bond breakage and Dess-Martin oxidation provides a modest 15% yield, an oxidation with catalytic TPAP yields a 94% of the desired ketone. 

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