Babler-Dauben Oxidation
The Babler-Dauben Oxidation is the catalytic chromium-mediated 1,3-oxidative transposition of allylic alcohols.
General features:
1. The reaction produces the desired enone product in high yields, and it doesn’t require air-free conditions nor heating. 2. A common solvent is anhydrous DCM or chloroform. 3. The main drawback is the use of the highly toxic oxidizing agent, PCC. 4. Besides, the Babler-Dauben oxidation of secondary allylic alcohols proves more difficult to control than that of tertiary analogues.
Babler-Dauben Oxidation
Reaction Mechanism
1. The cyclic tertiary allylic alcohol adds to pyridinium chlorochromate, PCC, to form the corresponding chromate ester. 2. 1,3-oxidative transposition affords the 3-alkyl α,β-unsaturated ketone.
Example
Experimental Procedure
To a stirred solution of the allylic alcohol (19.2 mmol, 1.0 eq) in dry DCM (300 mL) under argon were added Celite® (1.5 g per mmol of substrate) and finely ground PDC (3 eq). The dark brown suspension was stirred at rt in darkness for 12 h. After TLC indicating completion of the reaction, the mixture was filtered through a pad of silica gel, and concentrated under reduced pressure to give a residue, which was taken up with Et2O, filtered through a pad of silica gel, concentrated under reduced pressure, and finally purified by flash column chromatography to give the desired enone (86% yield over two steps).
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