Aqueous-phase one-pot synthesis of 2-aminothiazole- or 2-aminoselenazole-5- carboxylates from β-keto esters, thiourea or selenourea, and N-bromosuccinimide under supramolecular catalysis

Article abstract of DOI:10.1055/s-2007-990849

2-Amino-4-alkyl- and 2-amino-4-arylthiazole-5-carboxylates and their selenazole analogues were synthesized by α-halogenation of β-keto esters with N-bromosuccinimide, followed by cyclization with thiourea or selenourea, respectively, in the presence of β-

Full text of DOI:10.1055/s-2007-990849

PAPER
3469
Aqueous-Phase One-Pot Synthesis of 2-Aminothiazole- or 2-Aminoselenazole-
5-carboxylates from b-Keto Esters, Thiourea or Selenourea, and N-Bromo-
succinimide under Supramolecular Catalysis
S
ynthesis of 2-Aminot
e
hiazole
-
an
n
d
lenazole-5-
c
u
Durga Nageswar, Kakulapati Rama Rao*
Organic Chemistry Division-I, Indian Institute of Chemical Technology, Hyderabad 500 007, India
E-mail: drkrrao@yahoo.com
Received 15 June 2007; revised 29 August 2007
ardous organic solvents and involved tedious workup be-
Abstract: 2-Amino-4-alkyl- and 2-amino-4-arylthiazole-5-carbox-
ylates and their selenazole analogues were synthesized by a-haloge-
nation of b-keto esters with N-bromosuccinimide, followed by
cyclization with thiourea or selenourea, respectively, in the pres-
ence of b-cyclodextrin in water at 50 °C.
cause of the reagents used. In view of these shortcomings,
there is a need to develop a mild and eco-friendly synthet-
ic methodology for these high-value compounds by re-
placing organic solvents, most of which are flammable,
toxic, or carcinogenic, with water and by using a recycla-
ble catalyst as part of a green chemistry approach.19
Key words: thiazoles, selenazoles, b-keto esters, N-bromosuccin-
imide, cyclodextrins
Water is cheap, nontoxic, and the most readily available
reaction medium, making it an environmentally and eco-
nomically attractive solvent.20 However, the fundamental
problem in performing reactions in water is that many or-
ganic substrates are hydrophobic and insoluble. In our ef-
forts to develop biomimetic approaches through
supramolecular catalysis21 and also to overcome some of
the drawbacks of the existing methodologies for synthe-
sizing thiazole and selenazole derivatives, we have at-
tempted for the first time the aqueous-phase synthesis of
thiazole and selenazole derivatives from b-keto esters, N-
bromosuccinimide (NBS), and the appropriate thiourea or
selenourea in the presence of b-cyclodextrin (Scheme 1).
Thiazoles play a prominent role in nature and have broad
applications in agricultural and medicinal chemistry. For
example, the thiazole in vitamin B1 serves as an electron
sink, and its coenzyme form is important for the decarbox-
ylation of a-keto acids1 and is present in various natural
products2 and herbicides.3 A large number of thiazole de-
rivatives have emerged as active pharmaceutical ingredi-
ents in several drugs because of their potential antitumor,4
anti-hypertensive,5 anti-inflammatory,6 anti-hyperlipi-
demic,7 and other biological properties.8 Selenazole deriv-
atives also play an important role in antitumor and
antibacterial activities9 and inhibit lipopolysaccharide-
induced nitric oxide production in BV-2 cells.10 Several
groups have developed various methods for the synthesis
of these thiazole and selenazole derivatives. Hantzsch
synthesis is the most widely used methodology.11 Based
on this concept, some newer methods, such as cycloaddi-
tion of TosMIC (tosylmethyl isocyanide) to thione deriv-
atives,12 the Ugi reaction,13 oxidation of thiazoline and
thiazolidine ring systems,14 and others,15 have been devel-
oped.
NH2
N
S
S
R
NH2
O
O
3
H2N
β-cyclodextrin, H2O
NBS (2), 50 °C
5
R1
O
O
R1
R
O
NH2
1
H2N
N
NH2
In the last decade, further methods have been developed
for introducing various aryl and olefinic moieties onto the
thiazole ring system, such as palladium-mediated cou-
pling processes16 and the nucleophilic reaction of lithio-
thiazole to afford substituted thiazoles.17 Georgia and
Tsolomitis have also reported the synthesis of 5-acetami-
do-2-amino-4-phenylthiazoles by bromination of g-keto
esters.18 Many of the syntheses of thiazole and selenazole
derivatives have been reported because of the com-
pounds’ interesting reactivities and potential biological
activities. All of these reactions were carried out in haz-
Se
R = Me, i-Pr, t-Bu, Ph
1 = Me, Et, Bn
Se
4
R
R
O
O
R1
6
Scheme 1
Cyclodextrins, which are cyclic oligosaccharides with hy-
drophobic cavities, exert microenvironmental effects
leading to selective reactions. They catalyze reactions in-
volving supramolecular catalysis through noncovalent
bonding as seen in enzymes.22 These biomimetic reactions
can be effectively carried out in water without generating
any toxic waste products. Thus, mimicking biochemical
conditions with the reactions carried out in water will be
SYNTHESIS 2007, No. 22, pp 3469–3472
x
x.
x
x
.
2
0
0
7
Advanced online publication: 29.10.2007
DOI: 10.1055/s-2007-990849; Art ID: Z14707SS
© Georg Thieme Verlag Stuttgart · New York

3470
M. Narender et al.
PAPER
superior to chemical selectivity. These attractive features In this synthesis, the role of cyclodextrin appears to be to
of cyclodextrins prompted us to carry out the synthesis of allow the b-keto ester to dissolve and to activate it through
thiazole and selenazole derivatives from b-keto esters in hydrogen bonding, thereby promoting the reaction. In the
water in the presence of b-cyclodextrin as this is one of the absence of b-cyclodextrin, the reaction did take place after
most useful synthetic transformations.
long reaction times (12 h), but the yields were poor (15%)
and a mixture of products were formed. b-Cyclodextrin
can be easily recovered and reused. These reactions do
take place with a-cyclodextrin; however, b-cyclodextrin
was chosen as the catalyst since it is inexpensive and eas-
ily accessible.
In general, the reactions were carried out by the in situ for-
mation of the b-cyclodextrin complex of the b-keto ester
1 in water at 50 °C, followed by the addition of NBS (2)
and either thiourea (3) or selenourea (4); stirring at the
same temperature gave the corresponding thiazole 5 and
selenazole 6 derivatives in excellent yields (Table 1). The Thus, we have demonstrated, for the first time, the novel
treatment of b-keto esters with NBS may afford a-bromo- and efficient biomimetic conversion of b-keto esters into
b-keto esters as intermediates, which then undergo cy- thiazole and selenazole derivatives using easily accessible
clization with thiourea or selenourea to give the corre- NBS and the appropriate thiourea or selenourea with b-
sponding thiazole and selenazole derivatives. The cyclodextrin as a promoter and water as the reaction me-
reactions were smooth and succinimide was obtained as a dium. This novel methodology may find a wide range of
byproduct, which could be recycled to give NBS23 as de- applications.
scribed below. However, it was observed previously that
bromination of carbonyl compounds using NBS requires
Melting points were measured in an Electrothermal apparatus and
a radical initiator, such as 2,2¢-azobis(isobutyronitrile) or
are uncorrected. Infrared spectra were recorded on a Nicolet FT-IR
dibenzoyl peroxide.24
spectrophotometer. 1H NMR spectra were recorded in CDCl3 at 200
MHz or 300 MHz on a Varian-200 or Bruker-300 spectrometer us-
ing TMS as an internal standard. Mass spectra were recorded on a
V. G. autospectrometer using ESI and EI techniques. Column chro-
Table 1 Synthesis of Substituted Thiazole and Selenazole Ring
Systems in the Presence of b-Cyclodextrin
matography was performed with 60–120 mesh silica gel.
Entry Substrate
Producta
X
S
Time Yieldb
(h) (%)
All reactions were carried out without any special precautions in an
atmosphere of air. Ethyl acetoacetate (99%) was purchased from
Spectrochem. Ethyl 4-methyl-3-oxopentanoate (95%), methyl 4,4-
dimethyl-3-oxopentanoate (99%), ethyl 3-oxo-3-phenylpropanoate
(90%) and selenourea (99.9%) were purchased from Aldrich. Thio-
urea (99%) and NBS (98%) were purchased from S.D. Fine-Chem
Ltd. and β-cyclodextrin (99%) was purchased from Fluka. Benzyl
4-methyl-3-oxopentanoate was synthesized from ethyl 4-methyl-3-
oxopentanoate via transesterification.25
O
X
X
O
O
H2N
1
2
1.3 90
OEt
N
OEt
O
Se 1.5 92
O
H2N
O
O
O
3
4
5
6
7
S
1.4 88
4-Substituted 2-Aminothiazole- 5 and 2-Aminoselenazole-5-
carboxylates 6; General Procedure
OEt
N
OEt
b-Cyclodextrin (1 mmol) was dissolved in H2O (20 mL) by warm-
ing the mixture to 50 °C until a clear solution was formed. Then, b-
keto ester 1 (1 mmol) dissolved in acetone (1 mL) was added drop-
wise, followed by NBS (2; 1.2 mmol) and the appropriate thiourea
(3) or selenourea (4) (1.2 mmol). The mixture was stirred at 50 °C
until the reaction was complete (as monitored by TLC, see Table 1
for reaction times). The mixture was then extracted with EtOAc and
the extract was filtered. The organic layer was dried (anhyd
Na2SO4) and the solvent was removed under reduced pressure. The
resulting product was further purified by column chromatography
(EtOAc–hexane, 2:8). The aqueous layer was cooled to 5 °C and b-
cyclodextrin was recovered from it by filtration. To the filtrate that
contained succinimide and HBr, NaBrO3 and concd H2SO4 were
added,23 and the mixture was stirred for 30 min. Then, the mixture
was extracted with EtOAc and the solvent was removed under vac-
uum to regenerate NBS in an isolated yield of 75–80%.
Se 2.0 90
O
X
X
X
O
H2N
S
1.5 92
OBn
N
OBn
Se 2.0 93
O
O
H2N
S
1.3 87
OMe
N
OMe
8
9
Se 1.5 89
Ethyl 2-Amino-4-methylthiazole-5-carboxylate (Table 1, Entry
1)
White solid.
O
H2N
O
O
S
1.2 92
OEt
Mp 174–176 °C.
N
Ph
OEt
IR (KBr): 3372, 3300, 1675, 1650, 1516, 1279, 1095 cm–1.
1H NMR (CDCl3, 300 MHz): d = 1.35 (t, J = 7.9 Hz, 3 H), 2.05 (br
s, 2 H), 2.49 (s, 3 H), 4.25 (q, J = 7.9 Hz, 2 H).
Ph
10
Se 1.3 94
a All products were characterized by 1H NMR and infrared spectros-
copy, mass spectrometry, and elemental analysis.
ESI-MS: m/z = 187 (100) [M + 1]+.
b Isolated yields after column chromatography.
Synthesis 2007, No. 22, 3469–3472 © Thieme Stuttgart · New York

PAPER
Synthesis of 2-Aminothiazole- and 2-Aminoselenazole-5-carboxylates
3471
Anal. Calcd for C7H10N2O2S: C, 45.15; H, 5.41; N, 15.04; S, 17.22.
Found: C, 45.27; H, 5.28; N, 14.89; S, 17.09.
1H NMR (CDCl3, 200 MHz): d = 1.17 (d, J = 7.64 Hz, 6 H), 3.90
(sept, J = 7.64 Hz, 1 H), 5.20 (s, 2 H), 5.65 (br s, 2 H), 7.25–7.40
(m, 5 H).
Ethyl 2-Amino-4-methylselenazole-5-carboxylate (Table 1,
Entry 2)
White solid.
ESI-MS: m/z = 325 (100) [M + 2]+.
Anal. Calcd for C14H16N2O2Se: C, 52.02; H, 4.99; N, 8.67. Found:
C, 52.24; H, 5.12; N, 8.79.
Mp 163–165 °C.
IR (KBr): 3375, 3064, 2929, 2757, 1665, 1124, 1086 cm–1.
Methyl 2-Amino-4-tert-butylthiazole-5-carboxylate (Table 1,
Entry 7)
White solid.
1H NMR (CDCl3, 300 MHz): d = 1.35 (t, J = 7.03 Hz, 3 H), 2.05 (s,
3 H), 4.22 (q, J = 7.03 Hz, 2 H), 7.73 (br s, 2 H).
Mp 161–163 °C.
IR (KBr): 3442, 3285, 1691, 1504, 1256, 1085 cm–1.
1H NMR (CDCl3, 300 MHz): d = 1.40 (s, 9 H), 3.75 (s, 3 H), 5.50
(br s, 2 H).
MS (EI, 70 eV): m/z = 233 (100) [M+].
Anal. Calcd for C7H10N2O2Se: C, 36.06; H, 4.32; N, 12.02. Found:
C, 35.90; H, 4.20; N, 12.15.
Ethyl 2-Amino-4-isopropylthiazole-5-carboxylate (Table 1,
Entry 3)
White solid.
ESI-MS: m/z = 215 (100) [M + 1]+.
Anal. Calcd for C9H14N2O2S: C, 50.45; H, 6.59; N, 13.07; S, 14.96.
Found: C, 50.27; H, 6.38; N, 13.19; S, 15.17.
Mp 179–181 °C.
IR (KBr): 3386, 3304, 1659, 1511, 1305, 1081 cm–1.
Methyl 2-Amino-4-tert-butylselenazole-5-carboxylate (Table 1,
Entry 8)
White solid.
1H NMR (CDCl3, 200 MHz): d = 1.15 (d, J = 6.49 Hz, 6 H), 1.35 (t,
J = 6.49 Hz, 3 H), 3.85 (sept, J = 6.49 Hz, 1 H), 4.25 (q, J = 6.49
Hz, 2 H), 5.60 (br s, 2 H).
Mp 146–148 °C.
ESI-MS: m/z = 215 (100) [M + 1]+.
IR (KBr): 3403, 3308, 3156, 2956, 1687, 1642, 1468 cm–1.
Anal. Calcd for C9H14N2O2S: C, 50.45; H, 6.59; N, 13.07; S, 14.96.
Found: C, 50.32; H, 6.48; N, 13.19; S, 15.12.
1H NMR (CDCl3, 300 MHz): d = 1.40 (s, 9 H), 3.70 (s, 3 H), 7.30
(br s, 2 H)
ESI-MS: m/z = 263 (100) [M + 2]+.
Ethyl 2-Amino-4-isopropylselenazole-5-carboxylate (Table 1,
Entry 4)
White solid.
Anal. Calcd for C9H14N2O2Se: C, 41.39; H, 5.40; N, 10.73. Found:
C, 41.54; H, 5.62; N, 10.59.
Mp 192–194 °C.
IR (KBr): 3395, 3298, 3105, 2962, 1632, 1502 cm–1.
Ethyl 2-Amino-4-phenylthiazole-5-carboxylate (Table 1,
Entry 9)
White solid.
1H NMR (CDCl3, 300 MHz): d = 1.15 (d, J = 7.89 Hz, 6 H), 1.30 (t,
J = 7.06 Hz, 3 H), 3.85 (sept, J = 7.89 Hz, 1 H), 4.15 (q, J = 7.06
Hz, 2 H), 7.30 (br s, 2 H).
Mp 170–172 °C.
IR (KBr): 3394, 3280, 1657, 1516, 1301, 1168, 1089 cm–1.
1H NMR (CDCl3, 200 MHz): d = 1.25 (t, J = 7.32 Hz, 3 H), 4.18 (q,
J = 7.32 Hz, 2 H), 5.59 (br s, 2 H), 7.30–7.40 (m, 3 H), 7.60–7.70
(m, 2 H).
ESI-MS: m/z = 263 (100) [M + 2]+.
Anal. Calcd for C9H14N2O2Se: C, 41.39; H, 5.40; N, 10.73. Found:
C, 41.23; H, 5.25; N, 10.92.
ESI-MS: m/z = 249 (100) [M + 1]+.
Benzyl 2-Amino-4-isopropylthiazole-5-carboxylate (Table 1,
Entry 5)
White solid.
Anal. Calcd for C12H12N2O2S: C, 58.05; H, 4.87; N, 11.28; S, 12.91.
Found: C, 58.17; H, 5.08; N, 11.42; S, 12.77.
Mp 166–168 °C.
Ethyl 2-Amino-4-phenylselenazole-5-carboxylate (Table 1,
IR (KBr): 3380, 3316, 3161, 2957, 1692, 1646, 1517, 1470, 1306,
1264, 1194, 1086 cm–1.
Entry 10)
White solid.
1H NMR (CDCl3, 300 MHz): d = 1.17 (d, J = 7.53 Hz, 6 H), 3.85
(sept, J = 7.53 Hz, 1 H), 5.21 (s, 2 H), 5.51 (br s, 2 H), 7.25–7.40
(m, 5 H).
Mp 178–180 °C.
IR (KBr): 3404, 3274, 1648, 1513, 1292, 1071 cm–1.
1H NMR (CDCl3, 300 MHz): d = 1.15 (t, J = 7.41 Hz, 3 H), 2.95 (br
s, 2 H), 4.05 (q, J = 7.41 Hz, 2 H), 7.20–7.30 (m, 2 H), 7.50–7.60
(m, 3 H).
ESI-MS: m/z = 277 (100) [M + 1]+.
Anal. Calcd for C14H16N2O2S: C, 60.85; H, 5.84; N, 10.14; S, 11.60.
Found: C, 60.72; H, 5.98; N, 10.29; S, 11.49.
ESI-MS: m/z = 297 (100) [M + 2]+.
Anal. Calcd for C12H12N2O2Se: C, 48.82; H, 4.10; N, 9.49. Found:
C, 48.97; H, 4.25; N, 9.32.
Benzyl 2-Amino-4-isopropylselenazole-5-carboxylate (Table 1,
Entry 6)
White solid.
Mp 176–178 °C.
Acknowledgment
IR (KBr): 3385, 3285, 3134, 2961, 2926, 2860, 1664, 1633, 1500
cm–1.
We thank CSIR, New Delhi, India, for fellowships awarded to
M.N., M.S.R., V.P.K., B.S., and R.S.
Synthesis 2007, No. 22, 3469–3472 © Thieme Stuttgart · New York

3472
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(14) (a) Martin, L. M.; Hu, B.-H. Tetrahedron Lett. 1999, 40,
References
7951. (b) You, S.-L.; Kelly, J. W. J. Org. Chem. 2003, 68,
9506.
(1) Breslow, R. J. Am. Chem. Soc. 1958, 80, 3719.
(2) (a) You, S.-L.; Kelly, J. W. Chem. Eur. J. 2004, 10, 71.
(b) Kelly, J.; Schraft, W. C.; Kutscher, A. H.; Tuoti, F.
Antibiot. Chemother. 1959, 9, 87.
(3) Matsunaka, S.; Nakamura, H. Zasso Kenkyu 1972, 13, 29.
(4) (a) Kumar, Y.; Green, R.; Borysko, K. Z.; Wise, D. S.;
Wotring, L. L.; Townsend, L. B. J. Med. Chem. 1993, 36,
3843. (b) Ei-Subbagh, H. I.; AI-Obaid, A. M. Eur. J. Med.
Chem. 1996, 31, 1017.
(5) Tsuruni, Y.; Ueda, H.; Hayashi, K.; Takase, S.; Nishikawa,
M.; Kiyoto, S.; Kuhara, M. J. Antibiot. 1995, 48, 1066.
(6) (a) Miwatashi, S.; Arikawa, Y.; Kotani, E.; Miyamoto, M.;
Naruo, K.-I.; Kimura, H.; Tanaka, T.; Asahi, S.; Ohkawa, S.
J. Med. Chem. 2005, 48, 5966. (b) Papadopoulou, C.;
Geronikaki, A.; Hadjipavlou-Litina, D. Farmaco 2005, 60,
969; and references cited therein.
(7) Pereira, R.; Gaudon, C.; Iglesias, B.; Germain, P.;
Gronemeyer, H.; De Lera, A. R. Bioorg. Med. Chem. Lett.
2006, 16, 49.
(15) (a) Mustafa, S. M.; Nair, V. A.; Chittoor, J. P.; Krishnapillai,
S. Mini-Rev. Org. Chem. 2004, 1, 375. (b) Walek, W.;
Pallas, M.; Augustin, M. Tetrahedron 1976, 32, 623.
(c) Golankiewicz, B.; Januszczyk, P.; Gdaniec, M.;
Kosturkiewicz, Z. Tetrahedron 1985, 41, 5989. (d) Lin, Y.-
I.; Seifert, C. M.; Kang, S. M.; Dusza, J. P.; Lang, S. A. Jr.
J. Heterocycl. Chem. 1979, 16, 1377. (e) Short, K. M.;
Ziegler, C. B. Jr. Tetrahedron Lett. 1993, 34, 71.
(f) Wardakhan, W. W.; Elkholy, Y. M. Phosphorus, Sulfur
Silicon Relat. Elem. 2002, 177, 2661. (g) Hermitage, S. A.;
Cardwell, K. S.; Chapman, T.; Cooke, J. W. B.; Newton, R.
Org. Process Res. Dev. 2001, 5, 37.
(16) (a) Sapountzis, I.; Dube, H.; Lewis, R.; Gommermann, N.;
Knochel, P. J. Org. Chem. 2005, 70, 2445. (b) Lipshutz, B.
H.; Frieman, B.; Birkedal, H. Org. Lett. 2004, 6, 2305.
(c) Nicolaou, K. C.; King, N. P.; Finlay, M. R. V.;
Roschangar, F.; Vourloumis, D.; Vallberg, H.; Sarabia, F.;
Ninkovic, S.; Hepworth, D. Bioorg. Med. Chem. 1999, 7,
665. (d) Feuerstein, M.; Doucet, H.; Santelli, M. J.
Organomet. Chem. 2003, 687, 327. (e) Molander, G. A.;
Biolatto, V. J. Org. Chem. 2003, 68, 4302. (f) Hodgetts, K.
J.; Kershaw, M. T. Org. Lett. 2003, 5, 2911.
(8) (a) Millan, D. S.; Prager, R. H.; Brand, C.; Hart, P. H.
Tetrahedron 2000, 56, 811. (b) Wang, W.-L.; Yao, D.-Y.;
Gu, M.; Fan, M.-Z.; Li, J.-Y.; Xing, Y.-C.; Nan, F.-J. Bioorg.
Med. Chem. Lett. 2005, 15, 5284.
(9) (a) Shafiee, A.; Mazloumi, A.; Cohen, V. I. J. Heterocycl.
Chem. 1979, 16, 1563. (b) Shafiee, A.; Shafaati, A.;
Khamench, B. H. J. Heterocycl. Chem. 1989, 26, 709.
(c) Shafiee, A.; Khashayarmanesh, Z.; Kamal, F. J. Sci.,
Islamic Repub. Iran 1990, 1, 111. (d) Maeda, H.; Kambe,
N.; Sonoda, N.; Fujiwara, S.; Shin-ike, T. Tetrahedron 1997,
53, 13667.
(10) (a) Koketsu, M.; Ishihara, H.; Wu, W.; Murakami, K.; Saiki,
I. Eur. J. Pharm. Sci. 1999, 9, 157. (b) Wu, W.; Murakami,
K.; Koketsu, M.; Yamada, Y.; Saiki, I. Anticancer Res.
1999, 19, 5375. (c) Cho, S. I.; Koketsu, M.; Ishihara, H.;
Matsushita, M.; Nairn, A. C.; Fukazawa, H.; Uehara, Y.
Biochim. Biophys. Acta 2000, 1475, 207. (d) Koketsu, M.;
Choi, S. Y.; Ishihara, H.; Lim, B. O.; Kim, H.; Kim, S. Y.
Chem. Pharm. Bull. 2002, 50, 1594. (e) Gutzkow, K. B.;
Lahne, H. U.; Naderi, S.; Torgersen, K. M.; Skaalthegg, B.;
Koketsu, M.; Uehara, Y.; Blomhoff, H. K. Cell. Signalling
2003, 15, 871.
(11) (a) Metzger, J. V. In Comprehensive Heterocyclic
Chemistry, Vol. 6; Katritzky, A. R.; Rees, C. W., Eds.;
Pergamon: New York, 1984, 235–332. (b) Hantzsch, A.;
Weber, J. H. Ber. Dtsch. Chem. Ges. 1887, 20, 3118.
(c) Aguilar, E.; Meyers, A. I. Tetrahedron Lett. 1994, 35,
2473. (d) Varma, R. S. Pure Appl. Chem. 2001, 73, 193.
(e) Ochiai, M.; Nishi, Y.; Hashimoto, S.; Tsuchimoto, Y.;
Chen, D.-W. J. Org. Chem. 2003, 68, 7887; and references
cited therein.
(17) Dondoni, A. Synthesis 1998, 1681.
(18) Georgia, T.; Tsolomitis, A. Synth. Commun. 2006, 36, 501.
(19) (a) OECD (Organization for Economical Cooperation and
Development) Workshop on Sustainable Chemistry, Venice,
Italy, 1998. (b) Anastas, P. T.; Warner, J. C. Green
Chemistry: Theory and Practice; Oxford University Press:
Oxford, 1998. (c) Anastas, P. T.; Williamson, T. C.;
Hjeresen, D.; Breen, J. Environ. Sci. Technol. 1999, 33,
116A.
(20) (a) Jaeger, D. A.; Frey, M. R. J. Org. Chem. 1982, 47, 311.
(b) Jaeger, D. A.; Jamrozik, J.; Golich, T. G.; Clennan, M.
W.; Mohebalian, J. J. Am. Chem. Soc. 1989, 111, 3001.
(c) Jaeger, D. A.; Sayed, Y. M.; Dutta, A. K. Tetrahedron
Lett. 1990, 31, 449.
(21) (a) Surendra, K.; Krishnaveni, N. S.; Mahesh, A.; Rao, K. R.
J. Org. Chem. 2006, 71, 2532. (b) Krishnaveni, N. S.;
Surendra, K.; Rao, K. R. Chem. Commun. 2005, 669.
(c) Surendra, K.; Krishnaveni, N. S.; Reddy, M. A.;
Nageswar, Y. V. D.; Rao, K. R. J. Org. Chem. 2003, 68,
2058. (d) Krishnaveni, N. S.; Surendra, K.; Reddy, M. A.;
Nageswar, Y. V. D.; Rao, K. R. J. Org. Chem. 2003, 68,
2018.
(22) Szejtli, J.; Osa, T. Comprehensive Supramolecular
Chemistry, Vol. 3; Pergamon: New York, 1996.
(23) Fujisaki, S.; Hamura, S.; Eguchi, H.; Nishida, A. Bull. Chem.
Soc. Jpn. 1993, 66, 2426.
(24) Schmid, H.; Karrer, P. Helv. Chim. Acta 1946, 29, 573.
(25) Yadav, J. S.; Reddy, B. V. S.; Krishna, A. D.; Suresh Reddy,
Ch.; Narsaiah, A. V. J. Mol. Catal. A: Chem. 2007, 261, 93.
(12) Bergstrom, D. E.; Zhang, P.; Zhou, J. J. Chem. Soc., Perkin
Trans. 1 1994, 3029.
(13) Kazmaier, U.; Ackermann, S. Org. Biomol. Chem. 2005, 3,
3184.
Synthesis 2007, No. 22, 3469–3472 © Thieme Stuttgart · New York