The first one-pot synthesis of Morita-Baylis-Hillman adducts starting directly from alcohols

Article abstract of DOI:10.1055/s-0029-1219577

The first example of one-pot oxidative carbon-carbon bond formation via the Morita-Baylis-Hillman reaction using alcohols is reported. The protocol involves silica gel-DABCO catalyzed oxidation of alcohols to aldehydes with chloramine-T followed by their

Full text of DOI:10.1055/s-0029-1219577

LETTER
1047
The First One-Pot Synthesis of Morita–Baylis–Hillman Adducts Starting
Directly from Alcohols
S
L
ynthesisof Mo
a
rita–Baylis
l
–Hillman
Ad
D
ducts har Singh Yadav,* Vishnu Prabhakar Srivastava, Rajesh Patel
Green Synthesis Lab, Department of Chemistry, University of Allahabad, Allahabad 211002, India
Fax +91(532)2460533; E-mail: ldsyadav@hotmail.com
Received 5 January 2010
(
an aldehyde) of starting alcohol has to be isolated and
Abstract: The first example of one-pot oxidative carbon–carbon
bond formation via the Morita–Baylis–Hillman reaction using alco-
hols is reported. The protocol involves silica gel–DABCO catalyzed
6
then subjected to the MBH reaction in a separate step.
Oxidation of primary alcohols using different oxidants
7
oxidation of alcohols to aldehydes with chloramine-T followed by has been carried out by many workers. However, some of
their Morita–Baylis–Hillman reaction with acrylonitrile or methyl the more historically prominent methods have significant
drawbacks. Cr(VI) reagents (Jones,9 Ollins/Sarrett,
8
10
acrylate to give 70–87% overall yields of the corresponding
Morita–Baylis–Hillman adducts. The present work opens up a new
and efficient synthetic route to Morita–Baylis–Hillman adducts di-
rectly from alcohols in a one-pot operation.
11
PCC ) are toxic and their use often involves a difficult
workup. Swern oxidation requires low temperature, sol-
vent that can be difficult to remove, and generates stench.
TEMPO oxidant lacks tolerance for many functionl
12
Key words: oxidation, C–C bond formation, alcohols, chloramine-
T, silica gel–DABCO, Morita–Baylis–Hillman adducts
13
14,15
groups. The o-iodoxybenzoic acid (IBX)
is a mild and
selective reagent for this transformation, but its solubility
in common solvents remains a problem for which new so-
lutions are still to be sought. Furthermore, most of the
The Morita–Baylis–Hillman (MBH) reaction is an effi-
cient carbon–carbon bond-forming reaction between
Michael acceptors and carbonyl or imine compounds un-
der mild conditions. The reaction yields densely function-
16
above reagents leave acidic byproducts, which would
hamper the catalytic activity of the catalyst used for the
subsequent MBH reaction undergoing in the same vessel.
Advantageously, chloramine-T acts as an oxidizing agent
1
alized molecules, which can be utilized for the
2
construction of complex molecular frameworks. There-
17
in both acidic and alkaline solutions, and leaves TsNH2
fore, the MBH reaction has been drawing much attention
from synthetic organic chemists during the past decade.2
The major problem associated with this reaction is its
slow reaction rate. In view of this situation numerous
methods, including chemical as well as physical attempts,
have been made to accelerate the reaction with some good
and NaCl as byproducts, whose presence would not ad-
versely affect the ensuing MBH reaction, hence it is a
well-suited oxidant for the present study.
,3
Silica gel without modification is generally used for sepa-
ration of organic compounds in normal-phase chromatog-
raphy. Alternatively, silica should be an efficient aqueous
4
results.
18
organic reaction media because the organic substrate is
In general, the MBH reaction utilizes an aldehyde as one
of the starting materials. However, some of the aldehydes
are volatile, toxic, or unstable, especially because of aerial
oxidation. On the other hand, alcohols are usually more
stable, less volatile, and less toxic than the corresponding
aldehydes, meanwhile, oxidation of alcohols is an impor-
tant method for forming aldehydes. Moreover, one-pot se-
quential multistep reactions are of increasing academic,
economical, and ecological interest because they address
fundamental principles of synthetic efficiency and reac-
tion design. Thus, hitherto unexplored one-pot synthesis
of MBH adducts starting directly from alcohols is an in-
teresting target of investigation.
adsorbed to the silica by hydrophobic interaction between
the surface of the silica and the organic molecule. A sig-
19
nificant advantage of the silica medium is that the workup
20
procedure is extremely simple.
SiO2–DABCO
Ph
OH
+
chloramine-T
1
,4-dioxane
NaCl–
1a
2
Ts
PhCHO
+
TsNH2
4
N
Ph
3
a
path B
7
path A
CN
CN
5
a
5a
A number of procedures employing various reagents have
been developed for oxidative carbon–carbon bond forma-
OH
NHTs
5
tion. It is noteworthy that only few reports are available
CN
CN
Ph
Ph
in the literature on oxidative C–C bond formation via
MBH reaction, but in all these cases the oxidation product
6
a
8
Scheme 1 One-pot synthesis of MBH adduct 6a from benzyl alco-
hol
SYNLETT 2010, No. 7, pp 1047–1050
Advanced online publication: 10.03.2010
x
x.
x
x.
2
0
1
0
DOI: 10.1055/s-0029-1219577; Art ID: G00310ST
©
Georg Thieme Verlag Stuttgart · New York

1
048
L. D. S. Yadav et al.
LETTER
The above points and our continued work on MBH MBH reaction is accelerated in the presence of water.4j,n,q
3
i,j,21
chemistry
intrigued us to develop a one-pot synthesis Optimization of the catalyst revealed that among the cata-
of MBH adducts starting directly from alcohols employ- lysts tested, silica gel–DABCO gave the best result
ing chloramine-T as the oxidant. Initially, we investigated (Table 1, entries 5 and 7). It is worth noting that the cata-
the possibility of the formation of aza-MBH adduct 8 via lyst used exhibited distinguishing effects as manifested by
oxidative imine formation as depicted in Scheme 1, path yields (Table 1, entries 5 and 10–12). We also attempted
B. Thus, an equimolar mixture of alcohol 1a and chloram- the protic ionic liquid 1-methylimidazolium hydrogen
ine-T (2) in 1,4-dioxane using silica gel–DABCO catalyst sulfate [Hmim]HSO with DABCO under the same con-
4
and MS 4 Å, stirred at room temperature for 8 hours fol- ditions but the reaction proceeded very slowly and afford-
lowed by addition of 3 equivalents of acrylonitrile 5a and ed only 20% yield of 6a (Table 1, entry 1). This is
stirring at room temperature for 17 hours, the reaction pro- probably because the catalytic activity of DABCO for the
ceeded very slowly to afford only benzaldehyde (3a) and MBH reaction is inhibited by its protonation with
MBH adduct 6a (Scheme 1, path A). There was no forma- [Hmim]HSO . The optimum catalyst loading was 200 mg
4
tion of any appreciable amount of imine 7 or aza-MBH silica gel with 5 mmol of DABCO, which furnished 87%
adduct 8 under the present reaction conditions (Scheme 1, yield of adduct 6a (Table 1, entry 5).
path B). This urged us to develop a one-pot sequential ox-
The present optimized one-pot procedure for oxidative
idation–MBH reaction to prepare MBH adducts instead of
carbon–carbon bond formation via the MBH reaction in-
aza-MBH adducts. The key to effect a one-pot procedure
volves stirring of an equimolar mixture of an alcohol 1
is to explore appropriate reaction conditions.
and chloramine-T (2) in 1,4-dioxane–H O (1:1) using sil-
2
Thus, we turned our attention to optimize the conditions ica gel–DABCO catalyst system at room temperature for
for one-pot oxidative C–C bond formation between ben- 6–24 hours followed by addition of 3 equivalents of acry-
zyl alcohol and the Michael acceptor acrylonitrile via the lonitrile-methyl acrylate 5 and further stirring at room
MBH reaction (Scheme 1, path A). It was noted that on temperature for 5–45 hours to afford MBH adduct 6 in
addition of water as a co-solvent the reaction was signifi- 70–87% yields (Table 2).22 The reaction proceeded
cantly accelerated and that the binary medium consisting through sequential oxidation of alcohol 1 to aldehyde 3
of 1:1 ratio of 1,4-dioxane and water was found to be the and MBH reaction with acrylonitrile-methyl acrylate. p-
best solvent system (Table 1, entries 2–5). This is in con- Toluenesulfonamide formed as the oxidation byproduct
formity with the earlier observations that aqueous media was easily recovered after the reaction, converted into
are suitable for oxidation with chloramine-T, and the
Table 1 Optimization of Reaction Conditionsa
OH
catalyst
CN
Ph
OH
+
chloramine-T
2
Ph
CN
5a
1a
6a
Entry
Solvent
Catalyst
Yield (%)b
1
2
3
4
5
6
7
8
9
[Hmim]HSO –H O (1:1)
DABCO (5 mmol)
20
30
46
57
87
60
87
49
25
42
53
35
4
2
DMF–H O (1:1)
SiO (200 mg)–DABCO (5 mmol)
2
2
THF–H O (1:1)
SiO (200 mg)–DABCO (5 mmol)
2
2
1,4-dioxane–H O (2:1)
SiO (200 mg)–DABCO (5 mmol)
2
2
1,4-dioxane–H O (1:1)
SiO (200 mg)–DABCO (5 mmol)
2
2
1,4-dioxane–H O (1:1)
SiO (200 mg)–DABCO (2 mmol)
2
2
1,4-dioxane–H O (1:1)
SiO (200 mg)–DABCO (10 mmol)
2
2
DMF–H O (1:1)
SiO (200 mg)–DBU (5 mmol)
2
2
THF–H O (1:1)
SiO (200 mg)–DBU (5 mmol)
2
2
1
1
0
1
2
1,4-dioxane–H O (1:1)
SiO (200 mg)–DBU (5 mmol)
2
2
1,4-dioxane–H O (1:1)
DABCO (5 mmol)
DBU (5 mmol)
2
1
1,4-dioxane–H O (1:1)
2
a
Reaction conditions: 1a (5 mmol), chloramine-T (5 mmol), acrylonitrile (15 mmol), solvent (3 mL), time (25 h). For experimental procedure,
see ref. 22.
b
Yield of isolated and purified product 6a.
Synlett 2010, No. 7, 1047–1050 © Thieme Stuttgart · New York

LETTER
Synthesis of Morita–Baylis–Hillman Adducts
1049
Table 2 One-Pot Synthesis of MBH Adducts 6 Starting Directly
from Alcohols 1
References and Notes
(
1) (a) Morita, K.; Suzuki, Z.; Hirose, H. Bull. Chem. Soc. Jpn.
1968, 41, 2815. (b) Baylis, A. B.; Hillman, M. E. D.
Offenlegungsschrift 2155113, 1972; US 3,743,669, 1972;
Chem. Abstr. 1972, 77, 34174. (c) Ciganek, E. In Organic
Reactions, Vol. 51; Wiley: New York, 1997, 201.
OH
SiO2–DABCO
,4-dioxane–H2O, r.t.
1
EWG
+
chloramine-T
R
R
OH
EWG
1
2
5
6
(d) Ghosh, A. K.; Bilcer, G.; Schiltz, G. Synthesis 2001,
Time (h)a Yield (%)b,c
2203.
Entry
R
EWG
CN
(
2) (a) Basavaiah, D.; Rao, A. J.; Satyanarayana, T. Chem. Rev.
2003, 103, 811. (b) Basavaiah, D.; Rao, K. V.; Reddy, R. J.
Chem. Soc. Rev. 2007, 36, 1581. (c) Singh, V.; Batra, S.
Tetrahedron 2008, 64, 4511.
1
2
3
4
5
6
7
8
9
Ph
25
60
35
49
30
32
33
31
25
55
33
48
49
28
27
30
87
77
70
78
75
85
75
83
86
79
73
80
78
82
80
76
6
4-BrC H4
CN
(3) (a) Kim, J. N.; Lee, K. Y. Curr. Org. Chem. 2002, 627.
4-MeOC H4
CN
6
(
b) Wasnaire, P.; de Merode, T.; Marko, I. E. Chem.
Commun. 2007, 4755. (c) Kim, H. S.; Kim, H. S.; Kim, J. N.
Bull. Korean Chem. Soc. 2007, 28, 1841. (d) Cabrera, S.;
Aleman, J.; Bolze, P.; Bertelsen, S.; Jorgensen, K. A. Angew.
Chem. Int. Ed. 2008, 47, 121. (e) Ye, L.-W.; Han, X.; Sun,
X.-L.; Tang, Y. Tetrahedron 2008, 64, 1487. (f) Grange, R.
L.; Ziogas, J.; North, A. J.; Angus, J. A.; Schiesser, C. H.
Bioorg. Med. Chem. Lett. 2008, 18, 1241. (g) Cha, M. J.;
Song, Y. S.; Han, E.-G.; Lee, K.-J. J. Heterocycl. Chem.
3-O NC H
4
CN
2
6
4-ClC H4
CN
6
2
PhCH CH2
CN
2-furyl
CN
Et
CN
2
008, 235. (h) Sa, M. M.; Fernandes, L.; Ferreira, M.;
Bortoluzzi, A. J. Tetrahedron Lett. 2008, 49, 1228.
i) Yadav, L. D. S.; Srivastava, V. P.; Patel, R. Tetrahedron
Ph
COOMe
COOMe
COOMe
COOMe
COOMe
COOMe
COOMe
COOMe
(
1
1
1
1
1
1
0
1
2
3
4
5
6
4-BrC H4
6
Lett. 2009, 50, 1423. (j) Yadav, L. D. S.; Patel, R.;
Srivastava, V. P. Tetrahedron Lett. 2009, 50, 1335.
4-MeOC H4
6
(k) Reddy, C. R.; Kiranmai, N.; Johny, K.; Pendke, M.;
Naresh, P. Synthesis 2009, 399. (l) Nayak, M.; Batra, S.
Eur. J. Org. Chem. 2009, 3505.
3-O NC H
4
2
6
4-ClC H4
(4) (a) Isaacs, N. S. Tetrahedron 1991, 47, 8463.
6
(b) Rozendaal, E. L. M.; Voss, B. M. W.; Scheeren, H. W.
Et
Tetrahedron 1993, 49, 6931. (c) Roos, G. H. P.;
Rampersadh, P. Synth. Commun. 1993, 23, 1261. (d) Bode,
M. L.; Kaye, P. T. J. Chem. Soc., Perkin Trans. 1 1993,
n-C H
5
11
1809. (e) Kundu, M. K.; Mukherjee, S. B.; Balu, N.;
1
2-furyl
Padmakumar, R.; Bhat, S. V. Synlett 1994, 444.
a
Total time required for the conversion of alcohols 1 into MBH ad-
(f) Brzezinski, L. J.; Rafel, S.; Leahy, J. W. Tetrahedron
1997, 53, 16423. (g) Brzezinski, L. J.; Rafel, S.; Leahy, J.
W. J. Am. Chem. Soc. 1997, 119, 4317. (h) Almeida, W. P.;
Coelho, F. Tetrahedron Lett. 1998, 39, 8609.. (i) Masunari,
A.; Ishida, E.; Trazzi, G.; Almeida, W. P.; Coelho, F. Synth.
Commun. 2001, 31, 2127. (j) Yu, C.; Liu, B.; Hu, L. J. Org.
Chem. 2001, 66, 5413. (k) Balan, D.; Adolfsson, H. J. Org.
Chem. 2001, 66, 6498. (l) Balan, D.; Adolfsson, H. J. Org.
Chem. 2002, 67, 2329. (m) Aggarwal, V. K.; Dean, D. K.;
Mereu, A.; Williams, R. J. Org. Chem. 2002, 67, 510.
(n) Cai, J.; Zhou, Z.; Zhao, G.; Tang, C. Org. Lett. 2002, 4,
ducts 6, see ref. 22 for general procedure.
b
Yield of isolated and purified products.
c
4j,n,o,q,23
All compounds are known
and were characterized by com-
parison of their mp or bp, TLC, IR, and NMR data with those of au-
thentic samples prepared by literature methods.
chloramine-T on treatment with aqueous sodium hypo-
chlorite, and used in subsequent runs.
In summary, we have developed a one-pot process for
C–C bond formation via sequential oxidation of alcohols
to aldehydes and their Morita–Baylis–Hillman reaction
with acrylonitrile-methyl acrylate. This simple protocol
involves chloramine-T as oxidizing reagent and silica
gel–DABCO as the catalyst system. The present work
opens up a new, efficient, and one-pot synthetic route to
Morita–Baylis–Hillman adducts starting directly from al-
cohols.
4723. (o) Chandraekhar, S.; Narsihmulu, Ch.; Saritha, B.;
Sultana, S. S. Tetrahedron Lett. 2004, 45, 5865. (p) Mi, X.;
Luo, S.; Cheng, J.-P. J. Org. Chem. 2005, 70, 2338.
(
q) de Souza, R. O. M. A.; Pereira, V. L. P.; Esteves, P. M.;
Vasconcellos, M. L. A. A. Tetrahedron Lett. 2008, 49,
5902. (r) Bugarin, A.; Connell, B. T. J. Org. Chem. 2009, 74,
4638.
(
5) (a) Baran, P. S.; Ambhaikar, N. B.; G uerrero, C. A.;
Hafensteiner, B. D.; Lin, D. W.; Richter, J. M. ARKIVOC
2006, (vii), 310. (b) Lei, M.; Hu, R.-J.; Wang, Y.-G.
Tetrahedron 2006, 62, 8928. (c) Matsuo, J.-I.; Kawai, H.;
Ishibashi, H. Tetrahedron Lett. 2007, 48, 3155. (d) Huertu,
R.; Flores-Figueroa, A.; Ugalde-Saldivar, V. M.; Castillo, I.
Inorg. Chem. 2007, 46, 9510. (e) Clift, M. D.; Taylor, C. N.;
Tomson, R. J. Org. Lett. 2007, 9, 4667. (f) Konkol, L. C.;
Jones, B. T.; Thomson, R. J. Org. Lett. 2009, 11, 5550.
6) (a) Yeo, J. E.; Yang, X.; Kim, H. J.; Koo, S. Chem. Commun.
Acknowledgment
We sincerely thank SAIF, Punjab University, Chandigarh, for pro-
viding microanalyses and spectra. One of us (R.P.) is grateful to the
CSIR, New Delhi, for the award of a Junior Research Fellowship.
(
2
004, 236. (b) Krishna, P. R.; Kannan, V.; Sharma, G. V. M.
J. Org. Chem. 2004, 69, 6467.
Synlett 2010, No. 7, 1047–1050 © Thieme Stuttgart · New York

1
050
L. D. S. Yadav et al.
LETTER
(
7) (a) Tandon, M.; Krishna, P. K. Z. Phys. Chem. 1985, 266,
153. (b) Mantzavinos, D.; Hellenbrand, R.; Livingston,
A. G.; Metcalfs, I. S. Appl. Catal., B 1996, 11, 99.
(18) (a) Minakata, S.; Kano, D.; Oderaotoshi, Y.; Komatsu, M.
Angew. Chem. Int. Ed. 2004, 43, 79. (b) Minakata, S.;
Hotta, T.; Oderaotoshi, Y.; Komatsu, M. J. Org. Chem.
2006, 71, 7471.
1
(
c) Singh, R. A.; Singh, R. S. Oxid. Commun. 1997, 20, 248.
(
d) Konyukhov, V. Y.; Chernaa, I. V.; Naumov, V. A. Kinet.
(19) (a) Ando, T.; Kano, D.; Minakat, S.; Ryu, I.; Komatsu, M.
Tetrahedron 1998, 54, 13485. (b) Le Questel, J. Y.;
Berthelot, M.; Laurence, C. J. Phys. Org. Chem. 2000, 13,
347. (c) D’hooghe, M.; Rottiers, M.; Kerkaert, I.; De Kimpe,
N. Tetrahedron 2005, 61, 8746. (d) Minakata, S.; Hotta, T.;
Oderaostoshi, Y.; Komatsu, M. J. Org. Chem. 2006, 71,
7471. (e) Jung, Y.; Marcus, R. A. J. Am. Chem. Soc. 2007,
129, 5492. (f) Minakata, S.; Komatsu, M. Chem. Rev. 2009,
109, 711.
(20) Witula, T.; Holmberg, K. Langmuir 2005, 21, 3782.
(21) (a) Yadav, L. D. S.; Srivastava, V. P.; Patel, R. Tetrahedron
Lett. 2008, 49, 3142. (b) Yadav, L. D. S.; Srivastava, V. P.;
Patel, R. Tetrahedron Lett. 2008, 49, 5652. (c) Yadav, L. D.
S.; Patel, R.; Srivastava, V. P. Synlett 2008, 1789.
(d) Yadav, L. D. S.; Awasthi, C. Tetrahedron Lett. 2009, 50,
3801. (e) Yadav, L. D. S.; Rai, V. K. Tetrahedron Lett. 2009,
50, 2414. (f) Yadav, L. D. S.; Rai, V. K.; Singh, S. Synlett
2009, 1423.
Catal. 1997, 38, 811. (e) Navarro, M.; De Giovani, W. F.;
Romero, J. R. J. Mol. Catal. A: Chem. 1998, 135, 249.
(
J. Chem. Res. Synop. 2001, 274. (g) Svetlakov, N. V.;
Nikitin, V. G.; Orekhova, A. O. Russian J. Org. Chem. 2002,
f) Hirano, M.; Kojima, K.; Yakabe, S.; Morimoto, T.
3
8, 753. (h) Joseph, J. K.; Jain, S. L.; Sain, B. Eur. J. Org.
Chem. 2006, 590. (i) Kguchi, S.; Kitazume, T. Tetrahedron
Lett. 2006, 47, 2797. (j) Jiang, N.; Ragauskas, A. J.
Tetrahedron Lett. 2007, 48, 273.
(
(
8) Cainelli, G.; Cardillo, G. Chromium Oxidations in Organic
Chemistry; Springer: Berlin, 1984.
9) Harding, K. E.; May, L. M.; Dick, K. F. J. Org. Chem. 1975,
4
0, 1664.
10) Collins, J. C.; Hess, W. W.; Frank, F. J. Tetrahedron Lett.
968, 9, 3363.
(
1
(
(
(
11) Corey, E. J.; Suggs, J. W. Tetrahedron 1975, 31, 2647.
12) Omura, K.; Swern, D. Tetrahedron 1978, 34, 1651.
13) Annelli, P. L.; Montanari, F.; Quici, S. Org. Synth. 1990, 69,
(22) General Procedure for the Synthesis of MBH Adducts 6
A mixture of alcohol 1 (5 mmol), chloramine-T (2, 5 mmol),
DABCO (5 mmol), and SiO (200 mg) in 1,4-dioxane–H O
2
12.
14) (a) Frigerio, M.; Santagostino, M. Tetrahedron Lett. 1994,
5, 8019. (b) Frigerio, M.; Santagostino, M.; Sputore, S.;
Palmisano, G. J. Org. Chem. 1995, 60, 7272.
c) De Munari, S.; Frigerio, M.; Santagostino, M. J. Org.
(
2
2
3
(3 mL, 1:1) was stirred at r.t. until the chloramine-T was
consumed (6–24 h), then acrylonitrile or methyl acrylate (15
mmol) was added and the mixture was stirred at r.t. for 5–45
h (Table 2).The reaction progress was monitored by TLC.
Upon completion, the reaction mixture was evaporated
under reduced pressure and extracted with EtOAc (3 × 5
(
Chem. 1996, 61, 9272. (d) Frigerio, M.; Santagostino, M.;
Sputore, S. J. Org. Chem. 1999, 64, 4537.
(
15) (a) Zhdankin, V. V.; Stang, P. J. Chem. Rev. 2002, 102,
2
523. (b) Wirth, T. Angew. Chem. Int. Ed. 2005, 44, 3656.
mL). The combined organic phase was dried over MgSO ,
4
(
(
5
c) Ladziata, U.; Zhdankin, V. V. ARKIVOC 2006, (ix), 26.
d) Zhdankin, V. V.; Stang, P. J. Chem. Rev. 2008, 108,
299.
filtered, and evaporated under reduced pressure. The
resulting crude product was purified by silica gel column
chromatography using hexane–EtOAc as eluent to give pure
products 6. The structure of the products was confirmed by
comparison of their mp or bp, TLC, IR, and NMR data with
(
(
16) (a) Richardson, R. D.; Zayed, J. M.; Altermann, S.; Smith,
D.; Wirth, T. Angew. Chem. Int. Ed. 2007, 46, 6529.
4
j,n,o,q,23
(
b) More, J. D.; Finney, N. S. Org. Lett. 2002, 4, 3001.
17) (a) Banergi, K. K. Bull. Chem. Soc. Jpn. 1977, 50, 1616.
b) Kitagawa, H.; Mkaiyama, T. Chem. Pharm. Bull. 2002,
0, 1276. (c) Vinod, K. N.; Puttaswamy; Gowda, K. N. N.
Inorg. Chim. Acta 2009, 362, 2044.
authentic samples prepared by literature methods.
(23) Gong, H.; Cai, C.-Q.; Yang, N.-F.; Yang, L.-W.; Ahang, J.;
(
5
Fan, Q.-H. J. Mol. Catal. A: Chem. 2006, 249, 236.
Synlett 2010, No. 7, 1047–1050 © Thieme Stuttgart · New York

Copyright of Synlett is the property of Georg Thieme Verlag Stuttgart and its content may not
be copied or emailed to multiple sites or posted to a listserv without the copyright holder's
express written permission. However, users may print, download, or email articles for
individual use.