Scandium triflate as an efficient and useful catalyst for the synthesis of β-amino alcohols by regioselective ring opening of epoxides with amines under solvent-free conditions

Article abstract of DOI:10.1016/j.tetlet.2005.10.106

A simple and efficient method has been developed for the synthesis of β-amino alcohols by ring opening of epoxides in the presence of a catalytic amount of Sc(OTf)₃ at room temperature under solvent-free conditions. The reaction works well with both aromatic and aliphatic amines. High regio-, and diastereoselectivity can be considered as a noteworthy advantage of this method.

Full text of DOI:10.1016/j.tetlet.2005.10.106

Tetrahedron
Letters
Tetrahedron Letters 46 (2005) 9029–9034
Scandium triflate as an efficient and useful catalyst for the
synthesis of b-amino alcohols by regioselective ring opening of
epoxides with amines under solvent-free conditions
Andrew T. Placzek, James L. Donelson, Rushi Trivedi,
Richard A. Gibbs and Surya K. De*
Department of Medicinal Chemistry and Molecular Pharmacology, School of Pharmacy, Purdue Cancer Center,
Purdue University, West Lafayette, IN 47907, USA
Received 20 September 2005; revised 13 October 2005; accepted 20 October 2005
Available online 8 November 2005
Abstract—A simple and efficient method has been developed for the synthesis of b-amino alcohols by ring opening of epoxides in the
presence of a catalytic amount of Sc(OTf) at room temperature under solvent-free conditions. The reaction works well with both
3
aromatic and aliphatic amines. High regio-, and diastereoselectivity can be considered as a noteworthy advantage of this method.
Ó 2005 Elsevier Ltd. All rights reserved.
1
. Introduction
such as the rearrangement of epoxides to allyl alcohols
under basic conditions or polymerization in strongly
acidic conditions resulting in low yields of the desired pro-
ducts. In most cases, the reactions were carried out with
aromatic amines only. Moreover, the main disadvantage
of almost all existing methods is that the catalysts
are destroyed in the work-up procedure and cannot be
recovered or reused. To overcome these limitations, we
wish to report an efficient method for the ring opening
of epoxides with both aromatic and aliphatic amines
catalyzed by scandium triflate at room temperature.
b-Amino alcohols are versatile building blocks in the
synthesis of a wide range of biologically active natural
and synthetic products, unnatural amino acids, and
chiral auxiliaries. The classical synthesis of b-amino
alcohols involves the ring opening of epoxides with
amines; however, these reactions, which are generally
carried out with large excess of amines at elevated tem-
peratures, often fail when poorly nucleophilic amines or
sterically crowded amines/epoxides are concerned. In
addition, as a rule, these reactions are accompanied by
poor regioselectivity of ring opening. Subsequently, sev-
eral activators/promoters such as metal amides (lithium,
magnesium, lead, tin), metal alkoxide (DIPAT,
Ti(OiPr) , metal triflates (lithium, Ph SbOTf, lantha-
nide, tin,), metal halides (TaCl , ZrCl , VCl , ZnCl ,
CeCl ), silica under high pressure, ionic liquids,
1
2
3
4
Since the beginning of the new century, green chemistry
has become a major driving force for organic chemists
to develop environmentally benign routes to a myriad
of materials. The possibility of performing multi-com-
ponent reactions under solvent-free conditions with
solid catalysts could enhance their efficiency from an
economic as well as an ecological point of view, so sol-
vent free chemical reactions have received much atten-
tion. These reactions offer several advantages in
preparative procedures such as environmental compati-
bility, simplification of work-ups, formation of cleaner
products, enhanced selectivity, reduction of by-prod-
ucts, a reduction in waste produced, and much improved
reaction rates. Therefore, there is a need to develop new
methods for the synthesis of b-amino alcohols using less
hazardous solvents, or better, those that do not need sol-
vents at all. Therefore, there is further scope to search
5
6
4
4
7
5
4
3
2
10
8
9
3
1
clay,1 and others have been developed to perform
the epoxide ring opening reaction under mild condi-
tions. However, many of these methods often involve
the use of expensive and stoichiometric amounts of
reagents, air, and/or moisture sensitive catalysts, poor
regioselectivity especially with metal amides, long reac-
tion times, and also entail undesirable side reactions
12
*
Corresponding author. Fax: +765 494 1414; e-mail: skd125@
pharmacy.purdue.edu
0040-4039/$ - see front matter Ó 2005 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetlet.2005.10.106

9030
A. T. Placzek et al. / Tetrahedron Letters 46 (2005) 9029–9034
for a better catalyst in terms of operational simplicity,
reusability, and economic viability. There is also a need
to find out what works best under solvent-free
conditions.
tive ring opening of epoxides with amines. In the case
of cyclohexene oxide (Scheme 1 and Table 1), only one
isomer was formed. The aryl oxiranes underwent cleav-
age by a variety of amines in a regioselective fashion
with preferential attack at the benzylic position in the
presence of scandium triflate at room temperature in
neat (Schemes 1 and 2). Interestingly, the sterically
bulky 2,6-diisopropylaniline underwent the cleavage to
afford the corresponding b-amino alcohol in good yield.
Unlike previously reported methods, the present method
gave in good yields with aliphatic amines (entries 4, 5, 6
in Table 1 and entries 6, 7, 8 in Table 2). Aliphatic oxir-
anes gave the major product with the opposite regio-
chemistry of the aromatic substrate (entry 3, 4, 5 in
Table 3). Therefore, we suggest that the attack of nucleo-
phile is governed by the nature of oxirane and the
stability of carbonium ion. In aryl oxirane, the positive
charge on oxygen appears to be localized on the more
highly substituted benzylic carbon leading to the major
product (Scheme 3). For aliphatic oxirane gave the
opposite regiochemistry of the aromatic substrates, pos-
sibly steric factors predominate over electronic factors.
In case of propylene oxide (Table 3, entry 3) or glycidyl
tert-butyl ether (Table 3, entry 4), the selective nucleo-
philic attack at the less hindered carbon of epoxide
was observed. The cyclic aliphatic amines such as mor-
pholine, piperidine, pyrrolidine reacted with aliphatic
epoxide to afford in good yields. However, simple acy-
clic aliphatic amines such as pentyl amine and hexyl
amine did not give any satisfactory yields (20%) in the
reaction of aliphatic epoxide (propylene oxide). We iso-
lated starting materials and/or undesired products
(Scheme 4). The scope and generality of this method is
In the continuation of our work to develop new organic
transformations, we report herein that scandium triflate,
which acts as a mild Lewis acid, might be a useful and
inexpensive catalyst for the synthesis of b-amino
alcohols.
2
. Results and discussion
Most recently, there has been considerable interest
growing in the use of scandium triflate as a potential
1
3
Lewis acid in various organic reactions because the
catalyst is quite stable in water and reusable. The scan-
dium triflate is commercially available and can be used
for the synthesis of b-amino alcohols by the regioselec-
OH
O
Sc(OTf)3 (5 mol%)
Neat, rt
R1
R2
+
HN
R1
N
R2
1
2
3
a: R
c: R
e: R
1
= H, R
= H, R
= R = (CH
2
= C
= 4-ClC
; f: R
6
H
5
; b: R
; d: R
2 5
= R = (CH )
1
= H, R
2
= 4-MeC
6 4
H ;
1
1
2
6
H
1
4
1
= R
2
= C H CH ;
6 5 2
2
2
)
4
2
3
Scheme 1. Sc(OTf) -catalyzed epoxide ring opening of 1 with various
amines.
Table 1. Reactions of 1 with various amines under neat conditions at room temperature catalyzed by Sc(OTf)
3
a
Entry
Amine
Product
Time (h)
Yield (%)
NH2
OH
R
N
H
R
1
2
3
R = H
R = 4-Me
R = 4-Cl
R = H
R = 4-Me
R = 4-Cl
1
3
2
92
88
91
OH
4
5
3
2
86
90
Ph
NH2
N
H
Ph
OH
N
NH
OH
6
2
92
N
N
H
a
Isolated yields of the corresponding amino alcohol and in all cases one isomer was observed.

A. T. Placzek et al. / Tetrahedron Letters 46 (2005) 9029–9034
9031
R1
R2
O
N
OH
R1
OH
N
R1
R2
Sc(OTf)3 (5 mol%)
Neat, rt
R2
+
HN
+
4
2
5
6
a: R
1
= H, R
= H, R
= H; R
= R = (CH
2
= C
= 4-MeOC
= C CH
2 2
O(CH ) .
6
H
5
; b: R
1
= H, R
; d: R = H, R
2 5
; f: R = R = (CH ) ;
2
= 4-MeC
6 4
H ;
c: R
e: R
1
2
6
H
4
1
2
= 2,6-disopropyl-C H ;
6 3
1
2
6
)
H
5
2
1
2
g: R
1
2
2
2
3
Scheme 2. Regioselectivity in Sc(OTf) -catalyzed epoxide ring opening of 4 with various amines.
Table 2. Regioselectivity during the reaction of 4 with various amines in the presence of Sc(OTf)
3
at room temperature under neat conditions
a
b
Entry
Amine
Time (h)
Yield (%)
Ratio 5:6
NH2
R
1
2
3
4
R = H
R = 4-Me
R = 4-OMe
R = 4-NO
2
4
3
4
95
88
90
91
95:5
90:10
94:6
92:8
2
NH2
5
5
82
88:12
6
7
2
2
89
91
15:85
25:75
Ph
NH2
N
H
O
8
3
92
30:70
N
H
a
Isolated yields.
Regioisomers were determined using H NMR.
b
1
illustrated with respect to various epoxides and amines
and the results are presented in Tables 1–3.
the formation of complex metal salts with aliphatic
amines cause the catalyst destruction and make these
metal salts ineffective for use as catalysts for the opening
of epoxide rings by aliphatic amines. Due to the mild
In comparison with other catalysts such as CoCl , BiCl ,
2
3
TaCl , CeCl , VCl , Cu(OTf) , which are recently
acidic nature of Sc(OTf) , it works effectively for epox-
5
3
3
2
3
reported in the ring opening of styrene oxide with
ide ring opening reaction with aliphatic amines. The re-
sults summarized in Tables 1–3 reveal that the present
method is applicable for aromatic as well as aliphatic
amines.
amines, Sc(OTf) employed here shows more catalytic
3
reactivity than the others in terms of the amount of cat-
alyst required, reaction times, and yields of the product
(
Table 2). The efficacy of other catalysts such as InCl3,
RuCl , Nd(OTf) , Lu(OTf) , Yb(OTf) , was studied
3
3
3
3
for this reaction. Among these catalysts, Sc(OTf) was
3. Conclusion
3
found to be superior in terms of conversion and reaction
times (Table 4). The reported catalysts as shown in
Table 4 are not effective for reaction with benzyl amines.
Possibly these catalysts are strong Lewis acids making
In conclusion, Sc(OTf) is a new, highly efficient, and
reusable catalyst for the opening of epoxides with
amines leading to the generation of b-amino alcohols.
3

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A. T. Placzek et al. / Tetrahedron Letters 46 (2005) 9029–9034
Table 3. Reaction of various epoxides with aniline in the presence of Sc(OTf)
3
at room temperature under neat conditions
Time (h)
a
Entry
1
Epoxide
Product (major)
Yield (%)
b
O
NHPh
2
92
OH
Cl
Cl
OH
O
2
2
3
94
NHPh
OH
O
H
N
3
4
95
87
O
O
4
5
O
NHPh
O
OH
OH
b
5
85
NHPh
a
Isolated yields.
Other regioisomer 5–10% was determined using H NMR.
b
1
Sc(OTf) 3
O
Table 4. Ring opening of styrene oxide (4) with benzyl amine: effects of
catalysts
NHAr
O
Sc(OTf)3
Ar
OH
Entry
Catalyst
CoCl
BiCl
Yield (%)
Ar
Ar
1
2
3
4
5
6
7
8
0 (Ref. 14)
0 (Ref. 15)
0 (Ref. 8a)
0 (Ref. 8d)
0 (Ref. 8f)
0 (Ref. 16)
0 (Ref. 17)
0 (Ref. 18)
0
2
ArNH2
3
TaCls
3
Scheme 3.
VCl
CeCl
3
Cu(OTf)
HFIP
2
OH
Zr-salt
H
N
O
Sc(OTf)3
9
10
11
InCl
RuCl
Lu(OTf)
3
+
RNH2
3
0
72
R
Neat or CH2Cl2
3
1
1
1
2
3
4
Nd(OTf)
Yb(OTf)
Sc(OTf)
3
61
79
95
1
2h
3
Amine
Yield (%)
3
Pentyl amine
Hexyl amine
Morpholine
Piperidine
20
18
88
85
(CI, EI) were recorded on a Finnigan 4000 mass spec-
trometer. High resolution mass spectra (HRMS, EI,
CI, ESI) were recorded on a Finnigan MAT XL95 mass
spectrometer. The reactions were monitored by TLC,
and visualized with UV light followed by development
using 15% phosphomolybdic acid in ethanol. All sol-
vents and reagents were purchased from Aldrich with
high grade quality, and used without any purification.
All products are known and were identified by compari-
son with those reported in the literature.
Scheme 4.
The advantages of this method include (a) short reaction
times, (b) applications on both aromatic and aliphatic
amines, (c) high yields of products, (d) excellent regio-,
and stereoselectivity, (e) the use of relatively cheap com-
mercially available reusable reagents, and (f) solvent-
free conditions.
5. Typical procedure for reaction of epoxide with amine
4. Experimental
To a mixture of cyclohexene oxide (490 mg, 5 mmol)
and aniline (465 mg, 5 mmol), Sc(OTf)3 (123 mg,
0.25 mmol) was added at room temperature. After the
NMR spectra were recorded on a Bruker ARX 299
300 MHz) instrument. Low resolution mass spectra
(

A. T. Placzek et al. / Tetrahedron Letters 46 (2005) 9029–9034
9033
completion of reaction [TLC, R = 0.4 (30% ethyl
8.2 Hz, 1H), 3.26 (dd, J = 12.4, 3.4 Hz, 1H), 3.82 (m,
1H), 6.62 (d, J = 8 Hz, 2H), 6.89 (d, J = 8 Hz, 2H);
EIMS m/z 207 (M ), 190, 178, 135, 121, 107, 84, 57.
f
acetate in hexane)], the reaction mixture was partitioned
between ether (60 mL) and water (20 mL). The aqueous
layer containing the catalyst has been recovered and
reused for three times with a modest loss in activity
+
5.1.7. trans-2-(Phenylamino)cyclohexanol. Mp 61–
1
(
reaction yields: 87%, 69%, 55%). The organic layer
63 °C; H NMR (300 MHz, CDCl ) d 1.02–1.43 (m,
3
was washed with water (40 mL), aqueous NaHCO solu-
4H), 1.71–1.82 (m, 2H), 2.11–2.23 (m, 2H), 2.82 (brs, 1
H, NH), 3.14 (ddd, J = 4.1, 10.1, 10.2 Hz, 1H), 3.36
(ddd, J = 4.2, 10.2, 10.4 Hz, 1H), 6.71–7.23 (m, 5H);
3
tion (20 mL), and brine (40 mL), respectively, dried
(
MgSO ), and concentrated. The residue was purified
4
1
3
by column chromatography (30% ethyl acetate in hex-
C NMR (75 MHz, CDCl ) d 24.3, 25.4, 31.7, 33.2,
3
ane) to give a pure trans-2(phenylamino)cyclohexanol.
60.3, 74.5, 114.5, 118.5, 129.4, 147.9; EIMS m/z 191
(M ), 174, 99, 82, 77, 41.
1
+
H NMR (300 MHz, CDCl ) d 1.02–1.43 (m, 4H),
3
1
.71–1.82 (m, 2H), 2.11–2.23 (m, 2H), 2.82 (brs, 1 H,
NH), 3.14 (ddd, J = 4.1, 10.1, 10.2 Hz, 1H), 3.36 (ddd,
5.1.8. trans-2-(Benzylamino)cyclohexanol. Mp 73–
1
3
1
J = 4.2, 10.2, 10.4 Hz, 1H), 6.71–7.23 (m, 5H);
C
74 °C; H NMR (300 MHz, CDCl ) d 0.92–1.05 (m,
3
NMR (75 MHz, CDCl ) d 24.3, 25.4, 31.7, 33.2, 60.3,
1H), 1.12–1.32 (m, 3H), 1.65–1.72 (m, 2H), 1.96 (m,
1H), 2.12–2.29 (m, 2H), 2.84 (s, 1H), 3.18 (m, 1H),
3.62 (d, J = 12.8 Hz, 1H), 3.91 (d, J = 12.8 Hz, 1H),
3
+
7
4.5, 114.5, 118.5, 129.4, 147.9; EIMS m/z 191 (M ),
1
74, 99, 82, 77, 41.
1
3
7
.18–7.38 (m, 5H); C NMR (75 MHz, CDCl ) d
3
5
.1. Selected spectral data
24.6, 25.3, 30.7, 33.6, 51.1, 63.4, 74.1, 127.2, 128.4,
+
128.6, 140.9; EIMS m/z 205 (M ).
5
2
.1.1. 2-Anilino-2-phenyl-1-ethanol (entry 1, Table
1
). Liquid; H NMR (300 MHz, CDCl ) d 3.73 (dd,
3
References and notes
J = 10, 7 Hz, 1H), 3.94 (dd, J = 10, 4 Hz, 1H), 4.53
(
6
7
dd, J = 10.8, 6.8 Hz, 1H), 6.52 (d, J = 7.2 Hz, 2H),
1
. (a) Corey, E. J.; Zhang, F. Angew. Chem., Int. Ed. 1999,
38, 1931; (b) Johannes, C. W.; Visser, M. S.; Weatherhead,
G. S.; Hoveyda, A. H. J. Am. Chem. Soc. 1998, 120, 8340;
.72 (t, J = 7.2 Hz, 1H), 7.11 (t, J = 7.2 Hz, 2H), 7.31–
+
.45 (m, 5H); EIMS m/z 213 (M ), 195, 107, 77, 57.
(
1
c) Chang, B. L.; Ganesan, A. Bioorg. Med. Chem. Lett.
997, 7, 1511; (d) Rogers, G. A.; Parson, S. M.; Anderson,
1
5
.1.2. 2-(4-Methylphenyl)amino-2-phenyl-1-ethanol.
H
NMR (300 MHz, CDCl ) d 2.16 (s, 3H), 3.69 (dd,
J = 7.4, 11.2 Hz, 1H), 3.87 (dd, J = 4.2, 11.2 Hz, 1H),
.45 (dd, J = 4.2, 7.4 Hz, 1H), 6.48 (d, J = 8 Hz, 2H),
.92 (d, J = 8 Hz, 2H); C NMR (75 MHz, CDCl3) d
3
D. S.; Nilson, L. M.; Bahr, B. A.; Kornreich, W. D.;
Kaufman, R.; Jacobs, R. S.; Kirtman, B. J. Med. Chem.
1989, 32, 1217.
4
6
2
1
1
3
2. (a) OÕBrien, P. Angew. Chem., Int. Ed. 1999, 38, 326; (b)
Li, G.; Chang, H. T.; Sharpless, K. B. Angew. Chem., Int.
Ed. Engl. 1996, 35, 451.
0.5, 60.3, 66.9, 114.2, 119.6, 126.6, 127.3, 128.5,
+
29.6, 140.2, 144.8; EIMS m/z 227 (M ), 196, 77.
3
. Ager, D. J.; Prakash, I.; Schaad, D. R. Chem. Rev. 1996,
6, 835.
4. (a) Hodgson, D. M.; Gibbs, A. R.; Lee, G. P. Tetrahedron
9
5
.1.3. 1 2-(2,6-Diisopropylphenyl)amino-2-phenyl-1-etha-
nol. H NMR (300 MHz, CDCl ) d 1.18–1.27 (m,
2H), 3.04–3.27 (m, 4H), 4.95 (dd, J = 7.9, 3.6 Hz,
H), 7.02–7.46 (m, 8H); C NMR (75 MHz, CDCl3)
4.4, 27.6, 58.5, 73.4, 123.6, 124.2, 125.9, 127.8, 128.7,
3
1
4
996, 52, 14361; (b) Hanson, R. M. Chem. Rev. 1991, 91,
37; (c) Chini, M.; Croti, P.; Machia, F. J. Org. Chem.
1
1
2
1
1
1
3
1991, 56, 5939.
5
. (a) Kissel, C. L.; Rickborn, B. J. Org. Chem. 1972, 37,
2060; (b) Carre, M. C.; Houmounou, J. P.; Caubere, P.
Tetrahedron Lett. 1985, 26, 3107; (c) Yamada, J.; Yumoto,
M.; Yamamoto, Y. Tetrahedron Lett. 1989, 32, 4255; (d)
Fiorenza, M.; Ricci, A.; Taddel, M.; Tassi, D. Synthesis
+
42.2, 142.3, 142.8; EIMS m/z 297 (M ), 190, 175,
60, 107.
1
5
.1.4. 2-N-Benzylamino-1-phenyl-ethanol.
H
NMR
1
983, 640.
(
1
300 MHz, CDCl ) d 1.58 (br s, 2H), 2.77 (dd, J = 8.8,
2.1 Hz, 1H), 2.96 (dd, J = 3.7, 12.2 Hz, 1H), 3.82 (d,
J = 13.2 Hz, 1H), 3.88 (d, J = 13.2 Hz, 1H), 4.74 (dd,
J = 3.7, 8.8 Hz, 1H), 7.24–7.41 (m, 10H); C NMR
75 MHz, CDCl ) d 53.8, 56.7, 72.1, 126.2, 127.4,
3
6
7
. (a) Rampalli, S.; Chaudhari, S. S.; Akamanchhi, K. G.
Synthesis 2000, 22, 78; (b) Sagawa, S.; Abe, H.; Hase, Y.;
Inaba, T. J. Org, Chem. 1999, 64, 4962.
. (a) Auge, J.; Leroy, F. Tetrahedron Lett. 1996, 37, 7715;
(b) Fujiwara, M.; Imada, M.; Baba, A.; Matsuda, H.
Tetrahedron Lett. 1989, 30, 739; (c) Chini, M.; Croti, P.;
Favero, L.; Macchia, M.; Pineschi, M. Tetrahedron Lett.
1
3
(
1
3
27.8, 128.4, 128.7, 128.8, 140.2, 142.8; EIMS m/z 227
+
(
M ).
1
994, 35, 433; (d) Beaton, M.; Gani, D. Tetrahedron Lett.
5
1
4
6
.1.5. 2-(1-Piperidino)-1-phenylethanol. Mp 55–56 °C;
1998, 39, 8549.
8
. (a) Chandrasekhar, S.; Ramachandar, T.; Prakash, J. S.
Synthesis 2000, 1817; (b) Chakraborti, A. K.; Kondaskar,
A. Tetrahedron Lett. 2003, 44, 8315; (c) Swamy, N. R.;
Goud, T. V.; Reddy, S. M.; Krishnaiah, P.; Ven-
kateswarlu, Y. Synth. Commun. 2004, 34, 727; (d) Sabita,
G.; Reddy, G. S.; Reddy, K. V.; Yadav, J. S. Synthesis
H NMR (300 MHz, CDCl ) d 1.51(m, 2H), 1.60 (m,
3
H), 2.41 (m, 4H), 2.71 (m, 2H), 4.71 (dd, J = 3.7,
1
3
.6 Hz, 1H), 7.20–7.32 (m, 5H); C NMR (75 MHz,
CDCl ) d 21.2, 24.4, 26.2, 54.4, 66.9, 68.7, 125.5,
3
1
25.8, 127.5, 142.6.
2
003, 2298; (e) Pachon, L. D.; Gamez, P.; VanBrussel, J.
1
5
.1.6. 1-(4-Methylphenylamino)hexan-2-ol. Liquid; H
J.; Redijk, J. Tetrahedron Lett. 2003, 44, 6025; (f) Reddy,
L. R.; Reddy, M. A.; Bhanumati, N.; Rao, K. R. Synthesis
2001, 831.
NMR(300 MHz, CDCl ) d 0.92 (t, J = 6.9 Hz, 3H),
.24–1.63 (m, 6H), 2.21 (s, 3H), 2.94 (dd, J = 12.4,
3
1

9034
A. T. Placzek et al. / Tetrahedron Letters 46 (2005) 9029–9034
9
. Kotsuki, H.; Hayashida, K.; Shimanouchi, T.; Nishizawa,
H. J. Org. Chem. 1996, 61, 984.
Chakraborti, A.; Kondaskar, A.; Rudrawar, S. Tetrahe-
dron 2004, 60, 9085; (l) Wu, J.; Xio, H. G. Green Chem.
2005, 7, 708; (m) Azizi, N.; Saidi, M. R. Can J. Chem.
2005, 83, 505; (n) Kamal, A.; Ramu, R.; Azhar, M.;
Khanna, G. B. Tetrahedron Lett. 2005, 46, 2675, and
references cited therin.
1
1
1
0. Yadav, J. S.; Reddy, B. V.; Basak, A. K.; Narasaiah, A. V.
Tetrahedron Lett. 2003, 44, 1047.
1. Mojtahedi, M. M.; Saidi, M. R.; Bolrtchian, M. J. Chem.
Res. 1999, 128.
2. (a) Chini, M.; Crotti, P.; Macchia, M. Tetrahedron Lett.
13. (a) Kobayashi, S. Eur. J. Org. Chem. 1999, 73, 4961; (b)
Kobayashi, S.; Siguira, M.; Kitagawa, H.; Lam, W. W.
Chem. Rev. 2002, 102, 2227; (c) De, S. K.; Gibbs, R. A.
Tetrahedron Lett. 2005, 46, 1647.
14. Sundarajan, G.; Vijayakrishna, K.; Varghese, B. Tetra-
hedron Lett. 2004, 45, 8253.
1990, 31, 4661; (b) Harrak, Y.; Pujol, M. D. Tetrahedon
Lett. 2002, 43, 819; (c) Chini, M.; Crotti, P.; Flippin, L.
A.; Macchia, F. J. Org. Chem. 1991, 56, 7043; (d) Desai,
R. C. J. Org. Chem. 2001, 66, 4939; (e) Hine, J.; Linden, S.
M.; Kanagasabapathy, V. M. J. Am. Chem. Soc. 1985,
1
07, 1082; (f) Schneider, C.; Sreekanth, A. R.; Mai, E.
15. Ollevier, T.; Lavie-Compin, G. Tetrahedron Lett. 2002, 43,
7891.
16. Sekar, G.; Singh, V. K. J. Org. Chem. 1999, 64, 287.
17. Das, U.; Crousse, B.; Keasvan, V.; Bonnet-Delphon, D.;
Begue, J. P. J. Org. Chem. 2000, 65, 6749.
Angew. Chem., Int. Ed. 2004, 43, 5691; (g) Rafiee, E.;
Tangesnijad, S.; Habibi, M. H.; Mirkhani, V. Synth.
Commun. 2004, 34, 3673; (h) Khosrpour, A. R.; Khadaei,
M. M.; Ghozati, K. Chem. Lett. 2004, 33, 304; (i) Ollevier,
T.; Compin, G. L. Tetrahedron Lett. 2004, 45, 49; (j) Zhao,
P. Q.; Xu, L. W.; Xia, C. G. Synlett 2004, 856; (k)
18. Curini, M.; Epifano, F.; Marcotullio, M. C.; Rosati, O.
Eur. J. Org. Chem. 2001, 4149.