TEMPO, 2,2,6,6-Tetramethylpiperidinyloxy
2,2,6,6-Tetramethylpiperidinyloxy is a stable nitroxyl radical, which serves in oxidations as catalyst. By substitution in position 4 (4-hydroxy-TEMPO, 4-acetamido-TEMPO) its reactivity can be steered.
For example, processes with oxygen and 5 mol-% TEMPO permit environmentally benign reactions as alternatives to some oxidations, where so far e.g. chrome reagents were used.
Proposed mechanism for the oxidation of primary alcohols under basic
conditions
M. Angelin, M. Hermansson, H. Dong, O. Ramström, Eur. J. Org. Chem., 2006,
4323-4326.
Recent Literature
A rapid oxidation of primary and secondary alcohols using catalytic amounts of
TEMPO and Yb(OTf)3 in combination with a stoichiometric amount of
iodosylbenzene afforded carbonyl compounds in excellent yields without
over-oxidation. Oxidation of primary alcohols in the presence of secondary
alcohols proceeded with good selectivity.
J.-M. Vatèle, Synlett, 2006,
2055-2058.
An aerobic oxidation of primary and secondary alcohols to aldehydes and
ketones using TEMPO-CuCl as catalyst in the ionic liquid [bmin][PF6]
has been developed. The system needs no bubbling of O2 due to
its good solubility in the ionic liquid. The resulting aldehydes (with
no traces of carboxylic acids) and ketones can be extracted with organic
solvents. The ionic liquid can be reused after washing with water and
drying under high vacuum (8 runs for the oxidation of benzyl alcohol:
yields of 72%, 70, 68, 70, 65, 64, 62, and 60).
I. A. Ansari, R. Gree, Org. Lett., 2001, 1507-1509.
The combination of TEMPO and CAN can be used for the aerobic oxidation
of benzylic and allylic alcohols into their corresponding carbonyl
compounds. However, steric hindrance has been observed to impede the
reaction with some substituted allylic systems. The present method is
superior to others currently available due to its relatively short
reaction times and excellent yields.
S. S. Kim, H. C. Jung, Synthesis,
2003, 2135-2137.
A four-component system consisting of acetamido-TEMPO/Cu(ClO4)2/TMDP/DABCO
in DMSO allows an efficient room-temperature aerobic alcohol oxidation
of various alcohols into their corresponding aldehydes or ketones in
good to excellent yields. The catalytic system can be recycled.
N. Jiang, A. J. Ragauskas, J. Org. Chem., 2006,
71, 7087-7090.
The system Cu(ClO4)2/acetamido-TEMPO/DMAP catalyses
the room-temperature aerobic oxidation of primary alcohols to aldehydes in
the ionic liquid [bmpy]PF6. The catalysts can be recycled and
reused.
N. Jiang, A. J. Ragauskas, Org. Lett., 2005,
7, 3689-3692.
A highly efficient and mild procedure for the oxidation of different types of
alcohols uses TEMPO as catalyst, iodobenzene dichloride as stoichiometric
oxidant, and pyridine as base. Oxidation of 1,2-diols gives α-hydroxy ketones or
α-diketones depending on the amount of oxidant used. High yielding procedures
for the preparation of iodoarene dichlorides have been developed.
X.-F. Zhao, C. Zhang, Synthesis, 2007, 551-557.
X.-F. Zhao, C. Zhang, Synthesis, 2007,
551-557.
A highly convenient organocatalytic method for the mono-oxidation of
unprotected glycosides relies on the chemoselective properties of TEMPO
in combination with trichloroisocyanuric acid under very mild, basic
conditions. The resulting dialdo-glycosides are efficiently purified
with the use of solid-phase imine capture.
M. Angelin, M. Hermansson, H. Dong, O. Ramström, Eur. J. Org. Chem., 2006,
4323-4326.
An efficient and highly selective method for the oxidative conversion of
primary amines to the corresponding nitriles using trichloroisocyanuric
acid in the presence of catalytic TEMPO provides a new entry to the
synthesis of various aliphatic, aromatic and heterocyclic nitriles in
excellent yield.
F.-E. Chen, Y.-Y. Kuang, H.-F. Dai, L. Lu, M. Huo, Synthesis,
2003, 2629-2631.
Iodine was compared to other positive halogens as terminal oxidant in
chemoselective oxidations of alcohols using catalytic TEMPO and was shown to be
superior in cases of electron-rich and heteroaromatic benzylic alcohols.
R. A. Miller, R. S. Hoerrner, Org. Lett.,
2003, 5, 285-287.
A novel, metal-free oxidation system for the catalytic synthesis of aldehydes
and ketones using TEMPO and a quarternary ammonium salt as catalysts and Oxone
as oxidant proved especially successful for the synthesis of ketones. The mild
conditions tolerate even sensitive silyl protective groups which can otherwise
be cleaved in the presence of Oxone.
C. Bolm, A. S. Magnus, J. P. Hildebrand, Org. Lett., 2000,
2, 1173-1175.
C. Bolm, A. S. Magnus, J. P. Hildebrand, Org. Lett., 2000,
2, 1173-1175.
1 mol-% TEMPO and a catalytic amount of
1,3-dibromo-5,5-dimethylhydantoin and NaNO2 is a highly
efficient catalytic system for the aerobic oxidations of benzylic
alcohols in water.
R. Liu, C. Dong, X. Liang, X. Wang, X. Hu, J. Org. Chem., 2005,
70, 239-244.
