COMMUNICATIONS
Organocatalytic Aerobic Oxidation of a-Fluoroalkyl Alcohols
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1 should react with I to generate intermediate II,
which would lead to 2 and the reduced catalyst III.
The lack of ring opening in the oxidation of 1o
(entry 14, Table 2)[23] indicates that the formation of
an a-carbon radical from 1 is unlikely. Oxidation of
III to I by NO2 should finalize the catalytic cycle, and
NO2 should be regenerated via oxidation of NO with
O2 by producing H2Oor H2O2.
We have, in conclusion, demonstrated the first op-
erationally simple, organocatalytic, and aerobic oxida-
tion of a-fluoroalkyl alcohols to fluoroalkyl ketones
at room temperature. The success of this reaction
relies on the high oxidation potential of the keto-
ABNO catalyst. This method, which benefits from the
use of environmentally benign aerobic oxygen as an
oxidant, is broadly applicable to a wide variety of sub-
strates, and exhibits high functional-group tolerance
as well as high atom efficiency.
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Experimental Section
Typical Procedure for the Aerobic Oxidation of a-
Fluoroalkyl Alcohols using the Keto-ABNO/NOx
System
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4-Nitrophenyltrifluoromethanol (1g, 20.0 mg, 0.1 mmol),
keto-ABNO (0.77 mg, 0.005 mmol, 5 mol%), NaNO2
(0.69 mg, 0.01 mmol, 10 mol%) and AcOH (0.2 mL) were
mixed in a test tube. The mixture was stirred for 18 h at
room temperature under 1 atm of O2 (balloon). The mixture
was diluted with Et2O, neutralized with aqueous NaOH
(3N), and the phases were separated. The organic layer was
washed with brine, dried over Na2SO4, filtered, and the sol-
vent evaporated under reduced pressure. The resulting resi-
due was purified by flash column chromatography (SiO2, n-
hexane:EtOAc=2:1) to afford 4-nitrophenyl trifluoromethyl
ketone (2g) as a colorless oil; yield: 20.3 mg (93%).
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Acknowledgements
This work was supported by a Scientific Research C from
JSPS (for K.O.) and a Grant-in-Aid for Scientific Research
on Innovative Areas “Advanced Molecular Transformations
by Organocatalysts” from MEXT, Japan (for M.K.).
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