Investigation of catalytic activity of high-valent vanadium(IV) tetraphenylporphyrin: A new, highly efficient and reusable catalyst for acetylation of alcohols and phenols with acetic anhydride

Article abstract of DOI:10.1016/j.ica.2011.07.036

In the present work, the catalytic activity of high-valent tetraphenylporphyrinatovanadium(IV) trifluoromethanesulfonate, [V ^IV(TPP)(OTf)₂], in the acetylation of alcohols and phenols with Ac₂O is reported. This new V(IV) catalyst was used as an efficient catalyst for not only primary alcohols (benzylic and aliphatic) but also sterically-hindered secondary and tertiary alcohols with acetic anhydride and the corresponding acetates were obtained in 85-99% yield and 0.5-15 min. Acetylation of phenols with acetic anhydride was also performed to afford the desired acetates in 88-99% and 1.5-20 min. This catalyst can be reused several times without loss of its catalytic activity.

Full text of DOI:10.1016/j.ica.2011.07.036

Inorganica Chimica Acta 377 (2011) 159–164
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Note
Investigation of catalytic activity of high-valent vanadium(IV)
tetraphenylporphyrin: A new, highly efficient and reusable catalyst for
acetylation of alcohols and phenols with acetic anhydride
⇑
⇑
S. Abdolmanaf Taghavi, Majid Moghadam , Iraj Mohammadpoor-Baltork , Shahram Tangestaninejad,
Valiollah Mirkhani, Ahmad Reza Khosropour
Department of Chemistry, Catalysis Division, University of Isfahan, Isfahan 81746-73441, Iran
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 17 April 2011
Received in revised form 30 June 2011
Accepted 25 July 2011
Available online 2 August 2011
In the present work, the catalytic activity of high-valent tetraphenylporphyrinatovanadium(IV) trifluoro-
methanesulfonate, [VIV(TPP)(OTf)2], in the acetylation of alcohols and phenols with Ac2O is reported. This
new V(IV) catalyst was used as an efficient catalyst for not only primary alcohols (benzylic and aliphatic)
but also sterically-hindered secondary and tertiary alcohols with acetic anhydride and the corresponding
acetates were obtained in 85–99% yield and 0.5–15 min. Acetylation of phenols with acetic anhydride
was also performed to afford the desired acetates in 88–99% and 1.5–20 min. This catalyst can be reused
several times without loss of its catalytic activity.
Keywords:
Alcohols
Phenols
Ó 2011 Elsevier B.V. All rights reserved.
Acetylation
Vanadium porphyrin
Electron-deficient
1. Introduction
course of various transformations in a synthetic sequence, espe-
cially in the synthesis of fine chemicals and natural products. A
In the last decade, electron-deficient metalloporphyrins have
been used as mild Lewis acid catalysts. Suda and coworkers re-
ported the use of chromium and iron porphyrins in organic synthe-
sis. They used Cr(tpp)Cl for regioselective [3,3] rearrangement of
aliphatic allyl vinyl ethers and for Claisen rearrangement of simple
variety of homogeneous or heterogeneous catalysts such as iodine
[22], p-toluenesulfonic acid [23], alumina [24], zinc chloride [25],
cobalt chloride [26], montmorillonite K-10 and KSF [27], zeolite
HSZ-360 [28], zirconium sulfophenyl phosphonate [29], Sc(OTf)3
[30], TaCl5 [31], TMSOTf [32], Cu(OTf)2 [33], In(OTf)3 [34], magne-
sium bromide [35], bismuth(III) salts [36], ferric perchlorate ad-
sorbed on silica-gel [37], RuCl3 [38], InCl3 [39], Ce(OTf)3 [40],
Mg(ClO4)2 [41], ZrCl4 [42], Cp2ZrCl2 [43], ZrOCl2Á8H2O [44], Al
(OTf)3 [45], NaHSO4ÁSiO2 [46], La(NO3)3Á6H2O [47], NbCl5 [48],
Gd(OTf)3 [49], MoO3@Al2O3 [50] cerium polyoxometalate [51],
Zn(ClO4)2Á6H2O [52], Mg(NTf2)2 [53], Cu(BF4)2 [54], BiO(ClO4)2
[55], HClO4–SiO2 [56], HBF4–SiO2 [57], ZrO(OTf)2 [58], cobalt(II)
salen complex [59], zirconocene bis(perfluorooctanesulfonate)s
[60], CBr4 [61], phosphomolybdic acid [62], O-benzenedisulfoni-
mide [63] and iron(III) chloride [64] have been routinely reported
for acetylation of alcohols and phenols with Ac2O. Although these
procedures provide an improvement, many of these catalysts or
activators need long reaction times, drastic reaction conditions or
tedious work up, moisture sensitive or expensive of the catalyst.
Hence, introducing of new procedures to overcome these problems
is still in demand.
aliphatic allyl vinyl ethers, Fe(tpp)OTf for rearrangement of
a,b-
epoxy ketones into 1,2-diketones and rearrangement of monoalkyl1-
substituted epoxides into aldehydes, and Cr(tpp)OTf for highly
regio- and stereoselective rearrangement of epoxides to aldehydes
[1–7].
Recently, we reported the application of tin(IV) porphyrins in
organic transformations. These catalysts were used as efficient cat-
alysts for ring-opening of epoxides, and for conversion of alcohols
and phenols to trimethylsilyl ethers, tetrahydropyranyl ethers,
methoxymethyl ethers and acetates [8–19].
Developing mild and efficient methods for the protection of hy-
droxyl group of alcohols and phenols is of great importance in syn-
thetic organic chemistry. One of the most common methods for the
protection of these compounds is the formation of acetyl deriva-
tives [20,21]. These reactions are of great importance during the
Vanadium is required for normal health, and could act in vivo
either as a metal cation or as a phosphate analog, depending on
the oxidation state, V(lV) or V(V), respectively. Vanadium in a sea
⇑
Corresponding authors. Tel: +98 311 7932712; fax: +98 311 6689732.
E-mail addresses: moghadamm@sci.ui.ac.ir (M. Moghadam), imbaltork@sci.ui.a
c.ir (I. Mohammadpoor-Baltork).
0020-1693/$ - see front matter Ó 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.ica.2011.07.036

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S.A. Taghavi et al. / Inorganica Chimica Acta 377 (2011) 159–164
[VIV(TPP)(OTf)2]
Ac2O, CH3CN
R
OH
or
R
OAc
or
Ar OH
Ar OAc
O
N
N
N
N
Scheme 1. Acetylation of alcohols and phenols with Ac2O catalyzed by
V
[VIV(TPP)(OTf)2].
squirt (tunicate), a primitive vertebrate, is concentrated in blood
cells, apparently as the major cellular transition metal, but
whether it participates in the transport of dioxygen (as iron and
copper do) is not known. In proteins, vanadium is a cofactor in
an algal bromoperoxidase and in certain prokaryotic nitrogenases.
However, its oxidation state within organisms seems to be highly
variable. The biochemistry of vanadium potentially involves four
oxidation states that are relatively stable in aqueous solution.
SOCl2, CH2Cl2
Cl
V
N
N
N
N
+
These are V2+, V3+, VO2+, and VO2 (the oxidation states 2, 3, 4,
Cl
and 5, respectively) [65].
Here, we wish to report an efficient method for acetylation of
alcohols and phenols with acetic anhydride in the presence of reus-
able high-valent tetraphenylporphyrinatovanadium(IV) trifluo-
romethane sulfonate, [VIV(TPP)(OTf)2], at room temperature
(Scheme 1).
THF, 60 oC
AgOTf, 0.5 h
OTf
2. Experimental
N
N
N
V
AgCl +
Chemicals were purchased from Fluka and Merck chemical
companies. 1HNMR spectra were recorded in CDCl3 solvent on a
Bruker-Avance 400 MHz spectrometer using TMS as an internal
standard. Infrared spectra were run on a Philips PU9716 or Shima-
dzu IR-435 spectrophotometer. All analyses were performed on a
Shimadzu GC-16A instrument with a flame ionization detector
using silicon DC-200 or Carbowax 20M columns. Tetraphenylpor-
phyrin, [VO(TPP)] and [V(TPP)Cl2] were prepared according to the
literature [66–68].
N
OTf
Scheme 2. Preparation route for catalyst.
2.1. Preparation of tetraphenylporphyrinatovanadium(IV)
trifluoromethanesulfonate, [VIV(TPP)(OTf)2]
To a solution of V(TPP)Cl2 (0.97 g, 1 mmol) in THF (50 mL), at
55 °C, AgCF3SO3 (0.54 g, 2 mmol) was added. The solution was stir-
red at 55 °C for 30 min. The AgCl precipitate was filtered through a
0.45 lM filter. The resulting solution was evaporated at room tem-
perature. Then, the [VIV(TPP)(OTf)2] was extracted with CH2Cl2 and
the [VIV(TPP)(OTf)2] crystals were obtained after evaporation of
solvent at room temperature.
Visible spectrum: 456 (Soret), 585, 628 nm; m (KBr): 1030, 1168,
1224, 1298 cmÀ1 (belong to SO3 groups and porphyrin ring); CHNS
analyses: Calc. C, 57.44; H, 2.93; N, 5.83; S, 6.67. Found: C, 57.35; H,
2.88; N, 5.91, S, 6.65.
2.2. General procedure for acetylation of alcohol and phenols with
Ac2O catalyzed by [VIV(TPP)(OTf)2]
Fig. 1. UV–Vis spectrum of [VIV(TPP)(OTf)2].
To a solution of alcohol or phenol (1 mmol) and Ac2O (3 mmol
per OH group) in CH3CN (0.5 mL) was added [VIV(TPP)(OTf)2]
(0.5 mol% for alcohols and 1 mol% for phenols) and stirred at room
temperature. The progress of the reaction was monitored by GC.
After completion of the reaction, the solvent was evaporated,
Et2O (10 mL) was added and the catalyst was filtered. The filtrates
were washed with brine, dried over Na2SO4 and concentrated un-
der reduced pressure to afford the crude product.
was evaporated, Et2O (10 mL) was added, the catalyst was filtered
and reused.
3. Results and discussion
3.1. Acetylation of alcohols and phenols with Ac2O catalyzed by
[VIV(TPP)(OTf)2]
2.3. Catalyst reusability
Scheme 2 shows the preparation procedure of [VIV(TPP)(OTf)2].
As can be seen, first the [VIVO(TPP)], which is commercially avail-
able, was converted to [VIV(TPP)Cl2] with SOCl2. The [VIV(TPP)Cl2]
was converted to electron-deficient [VIV(TPP)(OTf)2] compound.
The reusability of catalyst was checked in the acetylation of 4-
chlorobenzyl alcohol. At the end of each reaction, the solvent

S.A. Taghavi et al. / Inorganica Chimica Acta 377 (2011) 159–164
161
Table 1
Acetylation of alcohols and phenols with acetic anhydride catalyzed by [VIV(TPP)(OTf)2].a
Entry
Substrate
Product
Time (min)
0.5
Yield (%)b,c
1
90
CH2OH
CH2OAc
2
3
CH2CH2OH
CH2CH2CH2OH
CH2OH
CH2CH2OAc
CH2CH2CH2OAc
CH2OAc
0.5
0.5
95 (91)
99 (96)
4
5
0.75
0.75
99 (95)
99
Cl
Cl
Cl
CH2OH
CH2OH
Cl
Cl
CH2OAc
CH2OAc
Cl
6
7
1.5
0.5
95
85
Cl
Cl
CH2OAc
CH2OH
MeO
MeO
MeO
MeO
CH2OAc
8
1
96 (93)
95
CH2OH
CH2OH
9
1.5
1.5
t-Bu
O2N
t-Bu
O2N
CH2OAc
CH2OAc
10
90
CH2OH
CH2OH
CH2OAc
11
1.5
90
NO2
NO2
12
13
2
95 (90)
99
OH
OAc
CH2OAc
CH2OAc
CH2OH
CH2OH
1.5
N
N
14d
5
99 (94)
15
16
1
1
98
99
OH
OH
OAc
OAc
17
18
1
2
98
95
OAc
OH
CHCH3
OH
CHCH3
OAc
OAc
OH
19
20
21
6
1
2
99
99
OH
OAc
CH3
CH3
OAc
CH3
H3C
C
H3C
C
CH3
95
OH
(continued on next page)

162
S.A. Taghavi et al. / Inorganica Chimica Acta 377 (2011) 159–164
Table 1 (continued)
Entry
Substrate
Product
Time (min)
1
Yield (%)b,c
98 (96)
OH
OAc
22d
23d
15
95
C
C
OH
OAc
a
Reaction conditions: alcohol (1 mmol), catalyst (0.005 mmol, 5 mg), Ac2O (3 equivalents per OH group), CH3CN (0.5 mL).
GC yield based on the starting alcohol.
The yields in the parentheses refer to isolated products.
b
c
d
These reactions were carried out at 50 °C.
Table 2
Acetylation of phenols with Ac2O catalyzed by [VIV(TPP)(OTf)2].a
Entry
Substrate
Product
Time (min)
Yield (%)b
97
OAc
OAc
1
OH
OH
3
2
Cl
OH
2
3
5
6
Cl
OAc
99
98
99
99
3
2
3
Cl
Cl
HO
OH
AcO
OAc
OH
OAc
OH
OAc
OH
OAc
7
8
3
99
99
HO
AcO
AcO
OH
OAc
OAc
OAc
CH3
1.5
HO
OH
OH
CH3
9
2
98
OH
OAc
10
11
12
2
2
2
99
99
99
H3C
H3C
H3C
H3C
OH
OAc
OH
OAc
OH
OAc
13
14
2
2
96
97
O2N
OH
O2N
OAc
OH
NO2
OAc
NO2
15
20
88
a
Reaction conditions: phenol (1 mmol), catalyst (0.01 mmol, 10 mg), Ac2O (3 equivalents per OH group), CH3CN (0.5 mL).
GC yield based on the starting alcohol.
b

S.A. Taghavi et al. / Inorganica Chimica Acta 377 (2011) 159–164
163
Fig. 1 shows the UV–Vis spectrum of this catalyst in which three
bands at 456 (Soret band), 585 and 628 nm (Q bands) were
observed.
perature and in CH3CN as solvent. The results, which are summa-
rized in Table 1, showed that this catalytic system efficiently
converted different primary, secondary and tertiary alcohols to
their corresponding acetates in 85–99% and short reaction times
at room temperature except for bulky alcohols such as anthra-
cene-9-methanol, 1-adamantanol and triphenylmethanol. In these
cases, the reactions were carried out at 50 °C. This may due to the
higher solubility of these compounds in CH3CN at 50 °C or may be
due to the steric hindrance of the compounds which prevents these
compounds to interact with the catalyst. In the case of benzylic
alcohols, the nature of substituent, electron-withdrawing or elec-
tron-donating, has no significant effect on the yield and reaction
time.
Under the same reaction conditions, which was described for
acetylation of alcohols, the acetylation of phenols with Ac2O in
the presence of [VIV(TPP)(OTf)2] at 50 °C was also investigated. As
can be seen in Table 2, different phenols were efficiently acetylated
by this catalytic system and the corresponding acetates were pro-
duced in 88–99%.
The Lewis acidity of this high-valent V(IV) species was investi-
gated in acetylation of alcohols and phenols with Ac2O. First, in
order to show the effect of OTfÀ groups on the catalytic activity
of [VIV(TPP)(OTf)2], different vanadium(IV) porphyrins such as
[VIVO(TPP)], [VIV(TPP)Cl2] and [VIV(TPP)(OTf)2] were used as
catalyst in the acetylation of 4-chlorobenzyl alcohol with Ac2O.
The results showed that the catalytic activity of these catalysts
is as following: [VIV(TPP)(OTf)2] (99%) > [VIV(TPP)Cl2] (55%) >
[VIVO(TPP)] (21%). These observations show that introducing of
triflate groups on the prophyrin moiety increases the electron-
deficiency of V(IV) species which in turns increases the catalytic
activity of [VIV(TPP)(OTf)2] in the acetylation reactions.
Therefore, acetylation of alcohols with Ac2O was carried out in
the presence of catalytic amounts of [VIV(TPP)(OTf)2] at room tem-
The actual mechanism is not clear at present. However, a plau-
sible explanation is that acetic anhydride is first activated by cata-
lyst to afford 1. The hydroxy compound attacks 1 which in turn
converts to the final product and releases the catalyst for the next
catalytic cycle (Scheme 3).
In order to show the advantage of the presented method in the
acetylation reactions, we have compared the obtained results in
the acetylation of benzyl alcohol with acetic anhydride catalyzed
by [VIV(TPP)(OTf)2] with some of those reported in the literature
(Table 3). It is clear that the presented method is superior in terms
of reaction time, catalyst amount, or product yield.
3.2. Catalyst reusability
The reusability of a catalyst is of great importance from
economical and environmental points of view.
The reusability of [VIV(TPP)(OTf)2] was checked in the acetyla-
tion of 4-chlorobenzyl alcohol with acetic anhydride. At the end
of each reaction, the solvent was evaporated, Et2O was added
and the catalyst was filtered. Then, the catalyst was used with fresh
4-chlorobenzyl alcohol and Ac2O. The obtained results showed that
after using the catalyst for several times (five consecutive times
Scheme 3. The proposed mechanism for acetylation of alcohols and phenols with
Ac2O.
Table 3
Comparison of the results obtained for the acetylation of benzyl alcohol catalyzed by [VIV(TPP)(OTf)2] with those obtained by the recently reported catalysts.
Catalyst
OAc
OH
Entry
Catalyst
Catalyst (mol%)
T (°C)
Time (min)
Yield (%)
Refs.
1
2
3
4
5
6
7
8
[VIV(TPP)(OTf)2]
[Sn(TPP)(OTf)2]
[Sn(TPP)(BF4)2]
I2
0.5
1
1
r.t.
r.t.
r.t.
r.t.
r.t.
r.t.
60 °C
r.t.
r.t.
r.t.
r.t.
r.t.
r.t.
r.t.
r.t.
r.t.
r.t.
r.t.
r.t.
0.5
1
1
90
99
99
99
98
90
84
77
97
97
98
96
99
95
85
98
100
93
100
–
[11]
[18]
[22]
[26]
[27]
[28]
[31]
[33]
[34]
10
0.5
20 mg
20 mg
10
2
0.1
10
5
1
5
0.1
1
1
1
CoCl2
240
60
60
–
30
15
35
60
5
10
30
12
15
600
0.5
Montmorillonite KSF
Zeolite HSZ-360
TaCl5
Cu(OTf)2
In(OTf)3
BiCl3
Bi(TFA)3
Bi(OTf)3
RuCl3
InCl3
Ce(OTf)3
Mg(ClO4)2
Cp2ZrCl2
ZrO(OTf)2
9
10
11
[36]
12
13
14
15
16
17
[38]
[39]
[40]
[41]
[43]
[58]
1
1

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S.A. Taghavi et al. / Inorganica Chimica Acta 377 (2011) 159–164
[22] P. Phukan, Tetrahedron Lett. 45 (2004) 4785.
[23] A.C. Cope, E.C. Herrich, Organic Synthesis Collective, vol. IV, Wiley, New York,
1963, p. 304.
were checked), the corresponding acetate was obtained without
any decrease in its yield.
[24] G.W. Breton, M.J. Kurtz, S.L. Kurtz, Tetrahedron Lett. 38 (1997) 3825.
[25] R.H. Baker, F.G. Bordwell, Organic Synthesis Collective, vol. III, Wiley, New
York, 1995, p. 141.
4. Conclusion
[26] J. Iqbal, R.R. Srivastava, J. Org. Chem. 57 (1992) 2001.
[27] H. Hagiwara, K. Morohashi, T. Suzuki, M. Ando, I. Yamamoto, M. Kato, Synth.
Commun. 28 (1998) 2001.
[28] R. Ballini, G. Bosica, S. Carloni, L. Ciaralli, R. Maggi, G. Sartori, Tetrahedron Lett.
39 (1998) 6049.
[29] M. Curini, F. Epifano, M.C. Marcotullio, O. Rosati, M. Rossi, Synth. Commun. 30
(2000) 1319.
[30] K. Ishihara, M. Kubota, H. Kurihara, H. Yamamoto, J. Org. Chem. 61 (1996)
4560.
[31] S. Chandrasekhar, T. Ramachander, M. Takhi, Tetrahedron Lett. 39 (1998)
3263.
[32] P.A. Procopiou, S.P.D. Baugh, S.S. Flack, G.G.A. Inglis, J. Org. Chem. 63 (1998)
2342.
[33] P. Saravanan, V.K. Singh, Tetrahedron Lett. 40 (1999) 2611.
[34] K.K. Chauhan, C.G. Frost, I. Love, Synlett (1999) 1743.
[35] S.V. Pansare, M.G. Malusare, A.N. Rai, Synth. Commun. 30 (2000) 2587.
[36] I. Mohammadpoor-Baltork, H. Aliyan, A.R. Khosropour, Tetrahedron 57 (2001)
5851.
Electron-deficient metalloporphyrins have been used as mild
Lewis acids. In this report, we demonstrated for the first time that
the tetraphenylporphyrinatovanadium(IV) trifuoromethanesulfo-
nate, [VIV(TPP)(OTf)2], can be considered as an efficient and mild
Lewis acid for catalytic acetylation of alcohols and phenols. The
advantage of this system is that even hindered substrates can be
acetylated with acetic anhydride in high yields. These points
clearly indicate that replacement of ClÀ with OTfÀ converts the
[V(TPP)Cl2] to an electron deficient catalyst, which can acts as a
super Lewis acid in organic transformations. In addition, short
reaction times and catalyst reusability make this catalytic system
as a useful method for acetylation reactions.
[37] A. Parmar, J. Kaur, R. Goyal, B. Kumar, H. Kumar, Synth. Commun. 28 (1998)
2821.
Acknowledgment
[38] S.K. De, Tetrahedron Lett. 45 (2004) 2919.
The financial support of this work by the Center of Excellence of
Chemistry of University of Isfahan (CECUI) is acknowledged.
[39] A.K. Chakraborti, R. Gulhane, Tetrahedron Lett. 44 (2003) 6749.
[40] R. Dalpozzo, A.D. Nino, L. Maiuolo, A. Procopiou, M. Nardi, G. Bartoli, R. Romeo,
Tetrahedron Lett. 44 (2003) 5621.
[41] A.K. Chakraborti, L. Sharma, R. Gulhane, R. Shivani, Tetrahedron 59 (2003)
7661.
References
[42] A.K. Chakraborti, R. Gulhane, Synlett (2004) 627.
[43] M.L. Kantam, K. Aziz, P.R. Likhar, Catal. Commun. 7 (2006) 484.
[44] R. Ghosh, S. Maiti, A. Chakraborty, Tetrahedron Lett. 46 (2005) 147.
[45] A. Kamal, M. Naseer, A. Khan, K. Srinivasa Reddy, Y.V.V. Srikanth, T. Krishnaji,
Tetrahedron Lett. 48 (2007) 3813.
[46] B. Das, P. Thirupathi, J. Mol. Catal. A: Chem. 269 (2007) 12.
[47] T. Srikanth Reddy, M. Narasimhulu, N. Suryakiran, K. Chinni Mahesh, K.
Ashalatha, Y. Venkateswarlu, Tetrahedron Lett. 47 (2006) 6825.
[48] J.S. Yadav, A.V. Narsaiah, A.K. Basak, P.R. Goud, D. Sreenu, K. Nagaiah, J. Mol.
Catal. A: Chem. 255 (2006) 78.
[49] R. Alleti, M. Perambuduru, S. Samantha, V. Prakash Reddy, J. Mol. Catal. A:
Chem. 226 (2005) 57.
[50] Jomy K. Joseph, Suman L. Jain, Bir Sain, J. Mol. Catal. A: Chem. 267 (2007)
108.
[51] V. Mirkhani, S. Tangestaninejad, M. Moghadam, B. Yadollahi, L. Alipanah,
Monatsh. Chem. 135 (2004) 1257.
[1] K. Suda, M. Sashima, M. Izutsu, F. Hino, J. Chem. Soc., Chem. Commun. (1994)
949.
[2] T. Takanami, R. Hirabe, M. Ueno, F. Hino, K. Suda, Chem. Lett. (1996) 1031.
[3] T. Takanami, M. Hayashi, K. Iso, H. Nakamoto, K. Suda, Tetrahedron 62 (2006)
9467.
[4] T. Takanami, M. Hayashi, K. Suda, Tetrahedron Lett. 46 (2005) 2893.
[5] K. Suda, K. Baba, S. Nakajima, T. Takanami, Chem. Commun. (2002) 2570.
[6] K. Suda, K. Baba, S. Nakajima, T. Takanami, Tetrahedron Lett. 40 (1999) 7243.
[7] K. Suda, T. Kikkawa, S. Nakajima, T. Takanami, J. Am. Chem. Soc. 126 (2004)
9554.
[8] S. Tangestaninejad, V. Mirkhani, Synth. Commun. 29 (1999) 2079.
[9] S. Tangestaninejad, M.H. Habibi, V. Mirkhani, M. Moghadam, J. Chem. Res. (S)
(2001) 365.
[10] S. Tangestaninejad, M.H. Habibi, V. Mirkhani, M. Moghadam, Synth. Commun.
32 (2002) 1337.
[52] R. Shivani, R. Gulhane, A.K. Chakraborti, J. Mol. Catal. A: Chem. 264 (2007) 208.
[53] A.K. Chakraborti, R. Shivani, J. Org. Chem. 71 (2006) 5785.
[54] A.K. Chakraborti, R. Gulhane, R. Shivani, Synthesis (2004) 111.
[55] A.K. Chakraborti, R. Gulhane, R. Shivani, Synlett (2003) 1805.
[56] A.K. Chakraborti, Rajesh Gulhane, Chem. Commun. (2003) 1896.
[57] A.K. Chakraborti, R. Gulhane, Tetrahedron Lett. 44 (2003) 3521.
[58] M. Moghadam, I. Mohammadpoor-Baltork, S. Tangestaninejad, V. Mirkhani, L.
Shariati, M. Babaghanbari, M. Zarea, J. Iran. Chem. Soc. 6 (2009) 523.
[59] F. Rajabi, Tetrahedron Lett. 50 (2009) 395.
[60] R. Qiu, Y. Zhu, X. Xu, Y. Li, L. Shao, X. Ren, X. Cai, D. An, S. Yin, Catal. Commun.
10 (2009) 1889.
[61] L. Zhang, Y. Luo, R. Fan, J. Wu, Green Chem. 9 (2007) 1022.
[62] S.T. Kadam, S.S. Kim, Synthesis (2008) 267.
[63] M. Barbero, S. Cadamuro, S. Dughera, P. Venturello, Synthesis (2008) 3625.
[64] M. Mihara, T. Nakai, T. Iwai, T. Ito, T. Ohno, T. Mizuno, Synlett (2010) 253.
[65] I. Bertini, H.B. Gray, S.J. Lippard, J.S. Valentine, Bioinorganic Chemistry,
University Science Books, 1994.
[66] A.D. Adler, F.R. Longo, J.D. Finarelli, J. Goldmacher, J. Assour, L. Korsakoff, J. Org.
Chem. 32 (1976) 476.
[67] S. Bencosme, M. Labady, C. Romero, Inorg. Chim. Acta 123 (1986) 15.
[68] P. Richard, J.L. Poncet, J.M. Barbe, R. Guilard, J. Goulon, D. Rinaldi, A. Cartier, P.
Tola, J. Chem. Soc., Dalton Trans. (1982) 1451.
[11] M. Moghadam, S. Tangestaninejad, V. Mirkhani, I. Mohammadpoor-Baltork, R.
Shaibani, J. Mol. Catal. A: Chem. 219 (2004) 73.
[12] M. Moghadam, S. Tangestaninejad, V. Mirkhani, R. Shaibani, Tetrahedron 60
(2004) 6105.
[13] S. Gharaati, M. Moghadam, S. Tangestaninejad, V. Mirkhani, I.
Mohammadpoor-Baltork, F. Kosari, Inorg. Chim. Acta 363 (2010) 1995.
[14] M. Moghadam, S. Tangestaninejad, V. Mirkhani, I. Mohammadpoor-Baltork, S.
Gharaati, Appl. Organomet. Chem. 23 (2009) 446.
[15] M. Moghadam, S. Tangestaninejad, V. Mirkhani, I. Mohammadpoor-Baltork, S.
Gharaati, Inorg. Chim. Acta 363 (2010) 1523.
[16] M. Moghadam, S. Tangestaninejad, V. Mirkhani, I. Mohammadpoor-Baltork, M.
Khajehzadeh, F. Kosari, M. Araghi, Polyhedron 29 (2010) 238.
[17] M. Moghadam, S. Tangestaninejad, V. Mirkhani, I. Mohammadpoor-Baltork,
S.A. Taghavi, J. Mol. Catal. A: Chem. 274 (2007) 217.
[18] M. Moghadam, S. Tangestaninejad, V. Mirkhani, I. Mohammadpoor-Baltork,
S.A. Taghavi, Catal. Commun. 8 (2007) 2087.
[19] M. Moghadam, S. Tangestaninejad, V. Mirkhani, I. Mohammadpoor-Baltork, S.
Gharaati, Polyhedron 29 (2010) 212.
[20] T.W. Greene, P.G.M. Wuts, Protective Groups in Organic Synthesis, 2nd ed.,
New York, Wiley, 1991.
[21] P.J. Kocienski, Protective Groups, in: R. Enders, R. Noyori, B.M. Trost (Eds.),
Stuttgart, Thieme, 1994.