urushibara nickel eros.ru003, biotransformation, Dokumenty [ Pobierz całość w formacie PDF ]
1
URUSHIBARA NICKEL
Urushibara Nickel
1
Use of Raney nickel results in an equimolar mixture of the two
stereoisomers. Hydrogenolysis of the resulting C–O bond can
occur with aryl-substituted compounds, giving the corresponding
hydrocarbons.
1
Ni
[7440-02-0]
Ni
(MW 58.69)
Dehydrogenations.
Urushibara catalysts have been used
as dehydrogenation catalysts. Numerous examples exist with
steroidal compounds using cyclohexanone as the hydrogen
acceptor. In general, dehydrogenations using Urushibara catalysts
are comparable to those of Raney nickel.
1
InChI = 1/Ni
InChIKey = PXHVJJICTQNCMI-UHFFFAOYAH
(precipitated metal hydrogenation catalyst; useful principally
in reduction of alkynes and alkenes to alkanes,
2
reduction of
alcohols,
3
dehydrogenations,
1
carbonyls
to
and
reductive
desulfurizations
1
)
Preparative Methods:
Urushibara catalysts are prepared by acid
(U-Ni-A), base (U-Ni-B), or neutral (U-Ni-N) digestion of
precipitated nickel. Similar catalysts can be prepared using
either iron or cobalt.
1
Handling, Storage, and Precautions:
Urushibara catalysts do not
appear to degrade upon short exposure to air.
4
Protection from
moisture is required for long-term storage.
H
U-Ni-A
H
2
(98 atm)
H
cyclohexane
35 °C, 2.5 h
80%
O
H
H
+
(2)
H
H
HO
HO
94:6
Urushibara Catalysts.
The Urushibara catalysts are a
family of precipitated metal catalysts that have been compared to
the more common
Raney Nickel
catalysts. Although the two can
catalyze many of the same reactions, Urushibara metals offer sev-
eral advantages: they are nonpyrophoric, are easily generated,
have a long shelf life, and can catalyze highly regio- and stereos-
elective reductions.
Catalytic Hydrogenation of Alkynes and Alkenes.
Alkenes
and alkynes can be reduced to the corresponding alkanes
using moderate to high pressures of H
2
and temperatures. In eq 1,
the exocyclic alkene is hydrogenated selectively with the use of
U-Ni-N. Longer hydrogenation times and use of other Urushibara
catalysts result in complete reduction of this substrate. The use
of Raney nickel in this example results in nonspecific reduction.
2
Aromatic rings can also be saturated; however, these reactions
only proceed at high temperature or under pressure.
1
Reductive Desulfurizations.
Urushibara catalysts, specif-
ically U-Ni-A, have been used in desulfurizations of sulfur-
containing compounds such as thiols, sulfides, disulfides, and
thioacetals without competing reduction of alkenes. Reductive
desulfurizations can be performed using Raney nickel with
comparable yields.
1
Miscellaneous Reductions.
Urushibara catalysts have been
employed to reduce oximes, nitriles, hydroxylamines, nitro, and
nitroso compounds. These reductions can be very dependent on
reaction conditions. Yields of products are generally high and
steric biasing can lead to high levels of stereocontrol.
1
1.
(a) Hata, K.
New Hydrogenating Catalysts
; Halsted: New York, 1971. (b)
Hata, K.; Motoyama, I.,
Org. Prep. Proced. Int.
1972
,
4
, 179. (c) Shiota,
M.,
Strem Chem.
1975
,
III
, 13.
U-Ni-N
H
2
(1 atm)
EtOH
30 °C, 25 min
77%
2.
(a) Kajitani, M.; Okada, J.; Ueda, T.; Sugimori, A.; Urushibara, Y.,
Chem.
Lett.
1973
, 777. (b) Kajitani, M.; Sasaki, Y.; Okada, J.; Ohmura, K.;
Sugimori, A.; Urushibara, Y.,
Bull. Chem. Soc. Jpn.
1974
,
47
, 1203.
(1)
3.
(a) Ishige, M.; Shiota, M.,
Synthesis
1973
, 171. (b) Ishige, M.; Shiota, M.;
Suzuki, F.,
Can. J. Chem.
1976
,
54
, 2581. (c) Ishige, M.; Shiota, M.,
Can.
J. Chem.
1975
,
53
, 1700.
Catalytic Hydrogenation of Carbonyl Compounds.
Ketones and aldehydes can be reduced to their respective alco-
hols using Urushibara catalysts with hydrogen at atmospheric
pressure and room temperature. eq 2 demonstrates the regio- and
stereoselectivity that can be obtained using Urushibara catalysts.
3
4.
Ishige, M.; Shiota, M.,
Can. J. Chem.
1975
,
53
, 1700.
Christopher R. Sarko & Marcello DiMare
University of California, Santa Barbara, CA, USA
Avoid Skin Contact with All Reagents
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