vanadium II chloride eros.rv002, biotransformation, Dokumenty [ Pobierz całość w formacie PDF ]
1
VANADIUM(II) CHLORIDE
Vanadium(II) Chloride
(90–95% yield),
4
and aryl azides to the corresponding amines
and N
2
(70–95% yield) (eq 3).
5
VCl
2
N
3
NH
2
VCl
2
[10580-52-6]
Cl
2
V (MW 121.84)
InChI = 1/2ClH.V/h2*1H;/q;;+2/p-2/f2Cl.V/h2*1h;/q2*-1;m
InChIKey = ITAKKORXEUJTBC-OUXHBNONCC
(3)
THF, H
2
O
R
R
R = H, 2-Me, 4-Cl, 4-F, 2-CF
3
(nitro group to carbonyl conversion; hydrodehalogenation of
-halo
ketones;
reductions;
reductive
cleavage
of
oximes;
reductive hydrolysis of 2,4-DNP derivatives)
Reductive Cleavage of Oximes.
Aqueous solutions of VCl
2
have been employed in the mildly exothermic deoximation of
oximes to the corresponding carbonyl compounds in 75–90%
yield (eq 4).
6
Alternate Names:
vanadium dichloride; vanadium chloride.
Physical Data:
mp 910
◦
C (subl);
d
3.23 g cm
−
3
.
Solubility:
sol with decomposition in hot and cold water; sol
alcohols, DMF, THF, ethers.
Form Supplied in:
commercially available as a green deliquescent
solid.
OH
OVCl
2
N
N
NH
VCl
2
H
+
THF, H
2
O
– VOCl
2
H
2
O
Vanadium(II) Chloride.
Many reagents based on chro-
mium(II), titanium(II), and titanium(III) ions have found utility
in organic synthesis because of their redox potentials (Table 1).
Vanadium(II) chloride has found application in modern organic
synthesis in part because its redox potential (+0.255 V) is
greater than the Sn
II
–Sn
III
couple (
−
0.15 V) although lower than
Cr
II
–Cr
III
O
(4)
87%
(+0.41 V) or Ti
II
–Ti
III
(+0.37 V).
1
A variety of syn-
thetic transformations have been documented.
Reductive Hydrolysis of 2,4-Dinitrophenylhydrazones.
The regeneration of carbonyl compounds from 2,4-dinitrophenyl-
hydrazones is often problematic owing to the acid stability of the
parent molecules. Vanadium chloride promotes the hydrolysis to
the respective carbonyl moiety in 67–95% yield via initial reduc-
tion of the nitro group.
7
Conversion of the Nitro Group to the Carbonyl Group.
When an aqueous solution of vanadium chloride is added to a pri-
mary or secondary aliphatic nitro compound dissolved in a mix-
ture of water, hydrochloric acid, and DMF, a moderate to good
yield (50–70% typically) of the corresponding ketone is isolated
(eq 1).
2
The pH-dependent procedure involves initial reduction
Other Vanadium(II) Reagents.
Aryl and alkyl halides are re-
duced by a number of low-valent transition metals.
8
The complex
9
VCl
2
(py)
4
reduces activated (e.g. Bn–Cl) but not unactivated
halo compounds (e.g. vinyl halides). This reagent is selective
towards the formation of coupled R–R products to the exclu-
sion of R–H-type products. In contrast, Cr
II
reduces
10
Bn–Cl
to various ratios of bibenzyl and toluene (dependent on the re-
action conditions). Bis(cyclopentadienyl)vanadium
11
(Cp
2
V) is
also effective in these reactions. In an extension of earlier work,
12
2,2,2-trichloroacetanilide has been selectively reduced to 2,2-
dichloroacetanilide using VCl
2
(py)
4
. Other complexes
13
of di-
valent vanadium having the general formula V(amine)
4
X
2
are
also known. The amine can be either aromatic (e.g. picoline) or
aliphatic (e.g. ethylenediamine). The V(amine)
4
X
2
chemistry
remains largely unexplored.
Recently, a bimetallic V
II
species, [V
2
Cl
3
(THF)
6
]
2
[Zn
2
Cl
6
],
prepared in situ from V
III
, has been introduced
14
to achieve the
stereoselective cross coupling of two different alkanals under mild
conditions. The intermolecular pinacol cross-coupling reaction
has been modified
15
to include chiral aldehydes which yield
syn
-
diols in a 91:9 diastereoisomeric ratio (up to 84% ee). Reduc-
tive cyclization of
,
-enals has also been demonstrated
16
to pro-
ceed with excellent stereoselectivity (eq 5), in contrast to what is
obtained with other reagents such as Sm
II
.
and
subsequent
hydrolysis
of
the
resulting
carbonyl
imine.
Several alternative methods are known
3
which will effect the
same transformation.
NO
2
O
VCl
2
DMF, H
2
O
(1)
53%
Hydrodehalogenation of
-Halo Ketones.
When an aqueous
solution of vanadium chloride is added to -halo ketones
1
in THF,
a mildly exothermic reaction ensues which yields the halogen-free
product after extractive workup (eq 2). Yields are generally quite
high, ranging between 80 and 98%.
O
O
Br
VCl
2
THF, H
2
O
(2)
98%
Br
Br
Reductions.
This
reagent
also
reduces
benzils
to
ben-
zoins (THF–H
2
O, 80–90% yield),
4
quinones to hydroquinones
Avoid Skin Contact with All Reagents
2
VANADIUM(II) CHLORIDE
[V
2
Cl
3
(THF)
6
]
2
[Zn
2
Cl
6
]
CH
2
Cl
2
7.
Olah, G. A.; Chao, Y.-L.; Arvanaghi, M.; Surya Prakash, G. K.,
Synthesis
1981
, 476.
CO
2
Me
CHO
68%
8.
Kustin, K.,
Prog. Inorg. Chem.
1969
,
13
, 107.
9.
Cooper, T. A.,
J. Am. Chem. Soc.
1973
,
95
, 4158.
CO
2
Me
CO
2
Me
+
(5)
10.
de Liefde Meijer, H. J.; Janssen, M. J.; van der Kerk, G. J. M.,
Recl. Trav.
Chim. Pays-Bas
1961
,
80
, 831.
OH
OH
11.
Eisch, J. J.; King, R. B.,
Org. Synth.
1965
,
1
, 65.
24:1
12.
Cooper, T. A.; Sonneberg, F. M.,
J. Org. Chem.
1975
,
40
, 55.
13.
Kamar, M. M.; Larkworthy, L. F.; Patel, K. C.; Philips, D. J.; Beech, G.,
Aust. J. Chem.
1974
,
27
, 41.
1.
Ho, T.-L.; Olah, G. A.,
Synthesis
1976
, 807.
14.
Raw, A. S.; Pedersen, S. F.,
J. Org. Chem.
1991
,
56
, 830.
2.
Kirchoff, R.,
Tetrahedron Lett.
1976
, 2533.
15.
Annunziata, R.; Cinquini, M.; Cozzi, F.; Giaroni, P.; Benaglia, M.,
Tetrahedron
1991
,
47
, 5737.
3.
(a) McMurry, J.; Melton, J.,
J. Am. Chem. Soc.
1971
,
93
, 5309.
(b) McMurry, J.; Melton, J.; Padgett, H.,
J. Org. Chem.
1974
,
39
, 259.
16.
Inokuchi, T.; Kawafuchi, H.; Torii, S.,
J. Org. Chem.
1991
,
56
, 4983.
4.
Ho, T.-L.; Olah, G. A.,
Synthesis
1976
, 815.
Benoit Vanasse & Michael K. O’Brien
Rhône-Poulenc Rorer Pharmaceuticals, Collegeville, PA, USA
5.
Ho, T.-L.; Henninger, M.; Olah, G. A.,
Synthesis
1976
, 815.
6.
Olah, G. A.; Arvanaghi, M.; Surya, G. K.,
Synthesis
1980
, 220.
A list of General Abbreviations appears on the front Endpapers
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