A clean, simple and efficient synthesis of trans-[3-(aryl)-2,3-dihydrofuro[3,2-h] quinolin-2-yl]-(4-chlorophenyl)methanones

Article abstract of DOI:10.3184/174751917X14967701767058

We report a green and efficient method for the synthesis of trans-[3-(aryl)-2,3-dihydrofuro[3,2-h]quinolin-2-yl]-(4-chlorophenyl) methanones from the condensation of 2-[2-(4-chlorophenyl)-2-oxoethyl)]isoquinolinium bromide with 8-hydroxyquinoline and an aromatic aldehyde in the presence of catalytic amounts of choline hydroxide in water at reflux conditions. This new protocol employing choline hydroxide, which is a green and inexpensive catalyst, offers advantages such as mild reaction conditions, short reaction time, high yields and does not involve any hazardous solvent. Therefore, this procedure can be classified as green chemistry.

Full text of DOI:10.3184/174751917X14967701767058

380 RESEARCH PAPER
VOL. 41 JULY, 380–383
JOURNAL OF CHEMICAL RESEARCH 2017
A clean, simple and efficient synthesis of trans-[3-(aryl)-2,3-dihydrofuro[3,2-h]
quinolin-2-yl]-(4-chlorophenyl)methanones
Maryam Salari , Alireza Hassanabadi *and Mohammad H. Mosslemin
a
b
a
a
Department of Chemistry, Yazd Branch, Islamic Azad University, Yazd, Iran
Department of Chemistry, Zahedan Branch, Islamic Azad University, Zahedan, Iran
b
We report a green and efficient method for the synthesis of trans-[3-(aryl)-2,3-dihydrofuro[3,2-h]quinolin-2-yl]-(4-chlorophenyl)
methanones from the condensation of 2-[2-(4-chlorophenyl)-2-oxoethyl)]isoquinolinium bromide with 8-hydroxyquinoline and an aromatic
aldehyde in the presence of catalytic amounts of choline hydroxide in water at reflux conditions. This new protocol employing choline
hydroxide, which is a green and inexpensive catalyst, offers advantages such as mild reaction conditions, short reaction time, high yields
and does not involve any hazardous solvent. Therefore, this procedure can be classified as green chemistry.
Keywords: 8-hydroxyquinoline, choline hydroxide, green chemistry, multi-component reaction, aromatic aldehydes, 4-chlorophenacyl bromide
Multi-component, one-pot syntheses have emerged as powerful
tools for their ability to produce products in a single operation from
three or more reactants with high atom economy. These reactions
are widely applied in biological and pharmaceutical chemistry for
producing different structures and combinatorial libraries for drug
oxoethyl)]isoquinolinium bromide 2 with 8-hydroxyquinoline 3
and an aromatic aldehyde 4 in the presence of catalytic amounts
of choline hydroxide in water under reflux conditions (Scheme 1).
Results and discussion
1
discovery. Dihydrofurans are important hetrocycles commonly
Treatment of isoquinoline with 4-chlorophenacyl bromide 1 in
acetonitrile yielded after 20 min, the 2-[2-(4-chlorophenyl)-2-
oxoethyl)]isoquinolinium bromide 2 in nearly quantitative yields
(Scheme 2).
The one-pot three-component reaction of 2-[2-(4-chlorophenyl)-
2-oxoethyl)]isoquinolinium bromide 2 with 8-hydroxyquinoline 3
and an aromatic aldehyde 4 in the presence of catalytic amounts
of choline hydroxide in refluxing water provided the furo[3,2-h]
quinolines 5 in excellent yields (Scheme 3).
2
,3
found in a large variety of naturally occurring substances. The
development of new and efficient methods for their synthesis
remains an area of current interest and a whole series of new
4
–17
synthetic methods have appeared in the literature. The methods
reported previously for the synthesis of dihydrofurans suffer from
severe disadvantages such as hazardous solvents, long reaction
times, inadequate yields and use of expensive non-recoverable
surfactants. Based on the above information and due to our
interest in developing synthetic strategies for the construction of
heterocyclic compounds, we have now used choline hydroxide as
a new green catalyst in a novel rapid method affording excellent
yields of dihydrofurans under reflux conditions.
The structures of compounds 5a–l were deduced from their
1
13
elemental analyses and their IR, H NMR and C NMR spectra.
The mass spectra of compounds 5a–l are fairly similar and display
1
molecular ion peaks. In the H NMR spectra, the two protons at
Recently, organic reactions in aqueous media have attracted
2,3-positions of the dihydrofuran ring display two doublets at 4.36
and 6.08 ppm with the vicinal coupling constant J = 5.2 Hz. It has
been documented that in cis-2,3-dihydrofuran the vicinal coupling
constant of the two methine protons is in the range J = 7–10 Hz,
while in trans-2,3-dihydrofurans the magnitude of the vicinal
18
a great deal of attention as a result of increasing interest in the
19
concepts of sustainability and green chemistry. In continuation of
2
0–23
our previous work, for the synthesis of heterocyclic compounds
we decided to investigate the reaction of 2-[2-(4-chlorophenyl)-2-
Scheme 1
O
Br CH CN, rt, 20 min
_
Br
3
O
+
+
N
N
Cl
2
1
Cl
Scheme 2
*
Correspondent. E-mail: ar_hasanabadi@yahoo.com

JOURNAL OF CHEMICAL RESEARCH 2017 381
Scheme 3
H O
2
+
N
OH
-
_
Br
Br
O
O
+
-
OH
N
+
N
OH
+
2
+
_
Cl
N
6
OH
O
Cl
N
O
4
-
N
OH
Ar
+
Ar
H
3
7
O
+
_
N
6
O
+
N
_
_
O
Cl
O
N
5
N
N
Ar
Ar
Cl
7
8
Scheme 4
coupling is smaller. So we concluded that the thermodynamically
A proposed mechanism for this reaction is shown in Scheme
4. The formation of the product can be explained as follows.
The 2-[2-(4-chlorophenyl)-2-oxoethyl)]isoquinolinium bromide
stable trans isomer of the 2,3-dihydrofuran derivatives were
2
4
formed.

382 JOURNAL OF CHEMICAL RESEARCH 2017
2
undergoes deprotonation in the presence of aqueous choline
trans-(4-Chlorophenyl)-3-(2-chlorophenyl)-2,3-dihydrofuro[3,2-h]
quinolin-2-yl)methanone (5d): Brown powder; m.p. 265–267 °C; IR
hydroxide to give the reactive isoquinolinium ylide 6 at room
temperature. The 8-hydroxyquinoline 3 reacts with aromatic
aldehyde 4 in the presence of choline hydroxide to give
the Knoevenagel product 7. This reacts instantly with the
isoquinolinium ylide 6 to form the zwitterionic intermediate
–1
(
KBr) (νmax/cm ): 2922, 2853, 1644, 1453, 1402, 1251, 1124, 755, 574.
Anal. calcd for C H Cl NO : C, 68.59; H, 3.60; N, 3.33; found: C,
24 15
2
2
1
6
8.75; H, 3.72; N, 3.20%. MS (m/z, %): 419 (4). H NMR (400 MHz,
CDCl ): δ 4.88 (d, J = 5.2 Hz, CH, 1H), 5.88 (d, J = 5.2 Hz, CH, 1H),
3
13
7
1
.25–8.30 (m, 13H, arom). C NMR (100.6 MHz, CDCl ): δ 40.7, 91.9,
16.2, 119.4, 120.5, 127.3, 127.5, 127.8, 128.3, 128.7, 129.4, 129.7, 130.3,
3
8
. The latter intermediate undergoes cyclisation with the
elimination of isoquinoline to give the desired product 5.
In summary, we herein report a simple and efficient one-
pot condensation of 2-[2-(4-chlorophenyl)-2-oxoethyl)]
isoquinolinium bromide with 8-hydroxyquinoline and an
aromatic aldehyde, in the presence of catalytic amounts of
choline hydroxide in water under reflux conditions to give
trans-[3-(aryl)-2,3-dihydrofuro[3,2-h]quinolin-2-yl]-(4-
chlorophenyl)methanones. The advantages of this method are
simple available starting materials, short reaction times, and an
easy clean work-up that affords excellent yields.
1
32.4, 133.4, 135.4, 135.7, 138.4, 138.7, 148.7, 155.2, 195.0.
t r a n s - ( 4 - C h l o r o p h e n y l ) - 3 - ( 4 - c h l o r o p h e n y l ) - 2 , 3 -
dihydrofuro[3,2-h]quinolin-2-yl)methanone (5e): Brown powder;
–1
m.p. 269–271 °C; IR (KBr) (νmax/cm ): 2924, 2824, 1646, 1412, 1250,
1024, 752, 534. Anal. calcd for C H Cl NO : C, 68.59; H, 3.60;
24 15 2 2
N, 3.33; found: C, 68.72; H, 3.75; N, 3.24%. MS (m/z, %): 419 (7).
1
H NMR (400 MHz, CDCl ): δ 4.97 (d, J = 5.0 Hz, CH, 1H), 6.01 (d, J
3
13
=5.0 Hz, CH, 1H,), 7.24–8.31 (m, 13H, arom). C NMR (100.6 MHz,
CDCl ): δ 45.6, 92.7, 116.3, 119.6, 120.7, 127.6, 128.3, 128.7, 129.3,
3
129.6, 130.2, 131.8, 132.3, 135.2, 138.5, 138.7, 141.1, 148.8, 155.2, 195.1.
trans-(4-Chlorophenyl)-3-(2-fluorophenyl)-2,3-dihydrofuro[3,2-h]
Experimental
quinolin-2-yl)methanone (5f): Brown powder; m.p. 244–246 °C; IR
–1
(
KBr) (νmax/cm ): 2922, 2853, 1644, 1453, 1402, 1255, 1124, 755, 574.
Melting points were determined with an Electrothermal 9100
apparatus. Elemental analyses were performed using a Heraeus CHN-
O-Rapid analyser. Mass spectra were recorded on a FINNIGAN-MAT
Anal. calcd for C H ClFNO : C, 71.38; H, 3.74; N, 3.47; found: C,
24 15
2
1
7
1.50; H, 3.62; N, 3.59%. MS (m/z, %): 403 (6). H NMR (400 MHz,
CDCl ): δ 5.08 (d, J = 5.4 Hz, CH, 1H), 6.05 (d, J = 5.4 Hz, CH, 1H),
3
8
430 mass spectrometer operating at an ionisation potential of 70 eV.
13
7
1
.25–8.27 (m, 13H, arom). C NMR (100.6 MHz, CDCl ): δ 41.1, 91.6,
16.1, 116.2, 119.6, 120.7, 124.8, 127.4, 127.8, 128.3, 128.7, 129.9, 130.1,
3
IR spectra were recorded on a Shimadzu IR-470 spectrophotometer.
1
13
H and C NMR spectra were recorded on Bruker DRX-400 Avance
spectrometer at solution in CDCl using TMS as internal standard.
130.4, 131.8, 135.6, 138.4, 138.7, 147.3, 155.9, 160.2, 195.3.
3
t r a n s - ( 4 - C h l o r o p h e n y l ) - 3 - ( 4 - m e t h ox y p h e n y l ) - 2 , 3 -
dihydrofuro[3,2-h]quinolin-2-yl)methanone (5g); Brown powder;
2
-[2-(4-Chlorophenyl)-2-oxoethyl)]isoquinolinium bromide 2 was
2
5
prepared by the literature method. Others chemicals used in this
work were purchased from Fluka (Buchs, Switzerland) and were used
without further purification.
–1
m.p. 197–199 °C; IR (KBr) (νmax/cm ): 1512, 1410, 1254, 1201, 1239,
175. Anal. calcd for C H ClNO : C, 72.20; H, 4.36; N, 3.37; found:
1
2
5
18
3
1
C, 72.35; H, 4.21; N, 3.50%. MS (m/z, %): 415 (9). H NMR (400
Synthesis of trans-[3-(aryl)-2,3-dihydrofuro[3,2-h]quinolin-2-yl]-
MHz, CDCl ): δ 3.81 (s, OCH , 3H), 4.99 (d, J = 4.8 Hz, 1H), 5.95
3
3
13
(
d, J = 4.8 Hz, 1H), 7.25–8.31 (m, 13H, arom). C NMR (100.6 MHz,
(
4-chlorophenyl)methanones: general procedure
To magnetically stirred solution of 2-[2-(4-chlorophenyl)-2-
oxoethyl)]isoquinolinium bromide (1 mmol), 8-hydroxyquinoline
CDCl ): δ 45.8, 55.9, 92.5, 114.6, 116.3, 119.7, 120.8, 127.4, 128.3,
a
3
128.7, 129.1, 130.2, 132.4, 135.2, 135.4, 138.6, 138.7, 147.5, 155.7, 158.7,
196.4.
(
1 mmol) and an aryl aldehyde (1 mmol) in H O (10 mL) was added
2
trans-(4-Chlorophenyl)-3-(4-fluorophenyl)-2,3-dihydrofuro[3,2-h]
quinolin-2-yl)methanone (5h): Brown powder; m.p. 239–241 °C; IR
choline hydroxide (0.0121 g, 0.1 mmol) in H O (4 mL). The mixture
2
was then refluxed for 5 h. The solid product was filtered and
recrystallised from ethanol to afford the pure product.
trans-(4-Chlorophenyl)-3-phenyl-2,3-dihydrofuro[3,2-h]quinolin-
–1
(
KBr) (νmax/cm ): 2924, 2824, 1646, 1412, 1272, 1117, 752, 534. Anal.
calcd for C H ClFNO : C, 71.38; H, 3.74; N, 3.47; found: C, 71.53; H,
2
4
15
2
1
3
5
(
1
.60; N, 3.61%. MS (m/z, %): 403 (4). H NMR (400 MHz, CDCl ): δ
.07 (d, J = 5.0 Hz, CH, 1H), 5.93 (d, J = 5.0 Hz, CH, 1H), 7.28–8.29
m, 13H, arom). C NMR (100.6 MHz, CDCl ): δ 46.1, 92.9, 117.4,
17.5, 119.3, 121.1, 127.4, 128.3, 128.7, 129.8, 130.2, 132.6, 135.2, 138.5,
3
2
-yl)methanone (5a): Brown powder; m.p. 257–259 °C; IR (KBr) (νmax/
–1
cm ): 2934, 2852, 1644, 1451, 1404, 1253, 1120, 1025, 753, 576. Anal.
calcd for C H ClNO : C, 74.71; H, 4.18; N, 3.63; found: C, 71.85; H,
13
3
2
4
16
2
1
4.32; N, 3.80%. MS (m/z, %): 385 (7). H NMR (400 MHz, CDCl ): δ
3
138.6, 138.7, 147.9, 155.6, 160.9, 195.6.
5
.07 (d, J = 5.4 Hz, CH, 1H), 5.98 (d, J = 5.4 Hz, CH, 1H), 7.27–8.65
trans-3- (4-Chloro-3-nitrophenyl) -2,3-dihydrofuro[3,2-h]
quinolin-2-yl)(4-chlorophenyl)methanone (5i): Brown powder;
13
(
m, 14H, arom). C NMR (100.6 MHz, CDCl3 : δ 42.3, 92.5, 116.2,
19.6, 120.7, 126.2, 127.4, 128.3, 128.7, 129.2, 130.2, 132.3, 135.2, 1385,
38.7, 143.1, 148.8, 155.2, 194.6.
1
1
–1
m.p. 232–234 °C; IR (KBr) (νmax/cm ): 2934, 2853, 1647, 1522, 1410,
245, 1123, 747, 575. Anal. calcd for C H Cl N O : C, 61.95; H, 3.03;
1
2
4
14
2
2
4
trans-(4-Chlorophenyl)-3-(2-nitrophenyl)-2,3-dihydrofuro[3,2-h]
N, 6.02; found: C, 62.08; H, 3.15; N, 5.90%. MS (m/z, %): 464 (5).
quinolin-2-yl)methanone (5b): Brown powder; m.p. 204–206 °C; IR
1
H NMR (400 MHz, CDCl ): δ 5.14 (d, J = 4.8 Hz, CH, 1H,), 6.02 (d,
–
1
3
(
5
KBr) (νmax/cm ): 2926, 2843, 1647, 1510, 1406, 1253, 1120, 1028, 745,
76. Anal. calcd for C H ClN O : C, 66.91; H, 3.51; N, 6.50; found:
13
J = 4.8 Hz CH, 1H), 7.29–8.31 (m, 13H, arom). C NMR (100.6 MHz,
2
4
15
2
4
CDCl ): δ 44.1, 93.1, 116.2, 119.6, 120.8, 125.3, 126.2, 127.4, 128.3,
3
1
C, 67.08; H, 3.40; N, 6.67%. MS (m/z, %): 430 (6). H NMR (400
128.7, 130.4, 132.2, 133.4, 135.4, 135.7, 138.6, 138.7, 142.2, 148.1,
MHz, CDCl ): δ 5.12 (d, J = 5.2 Hz, CH, 1H,), 5.95 (d, J = 5.2 Hz CH,
3
148.8, 155.2, 195.5.
13
1
H), 7.25–8.26 (m, 13H, arom). C NMR (100.6 MHz, CDCl ): δ 41.2,
3
trans-2-(4-Chlorobenzoyl)-2,3-dihydrofuro[3,2-h]quinolin-3-yl)
benzonitrile (5j): Brown powder; m.p. 212–214 °C; IR (KBr) (νmax/
91.5, 116.2, 119.6, 120.7, 124.4, 127.4, 128.3, 128.7, 129.1, 130.2, 132.3,
135.2, 135.7, 138.5, 138.7, 145.4, 148.7, 149.2, 155.4, 195.2.
–1
cm ): 2934, 2853, 1647, 1522, 1410, 1242, 747, 575. Anal. calcd for
trans-(4-Chlorophenyl)-3-(4-nitrophenyl)-2,3-dihydrofuro[3,2-h]
quinolin-2-yl)methanone (5c): Brown powder; m.p. 201–203 °C; IR
C H ClN O : C, 73.08; H, 3.68; N, 6.82; found: C, 73.24; H, 3.83; N,
2
5
15
2
2
1
6
.70%. MS (m/z, %): 410 (3). H NMR (400 MHz, CDCl ): δ 5.12 (d,
3
–1
(
KBr) (νmax/cm ): 2934, 2853, 1647, 1522, 1452, 1413, 1251, 118, 747,
J = 5.0 Hz, CH, 1H), 6.01 (d, J = 5.0 Hz, CH, 1H), 7.25–8.28 (m, 13H,
arom). C NMR (100.6 MHz, CDCl ): δ 45.8, 92.5, 110.1, 116.2, 118.6,
13
5
75. Anal. calcd for C H ClN O : C, 66.91; H, 3.51; N, 6.50; found: C,
2
4
15
2
4
3
1
67.05; H, 3.38; N, 6.63%. MS (m/z, %): 430 (8). H NMR (400 MHz,
119.6, 120.7, 127.5, 128.3, 128.5, 129.1, 130.6, 132.1, 132.8, 135.3,
CDCl ): δ 5.17 (d, J = 4.8 Hz, CH, 1H), 6.05 (d, J = 4.8 Hz, CH, 1H),
138.5, 138.7, 147.4, 148.8, 155.3, 194.8.
3
13
7
.26–8.27 (m, 13H, arom). C NMR (100.6 MHz, CDCl ): δ 45.8,
trans-(4-Chlorophenyl)-3- (p-tolyl)-2,3-dihydrofuro[3,2-h]
quinolin-2-yl)methanone (5k): Brown powder; m.p. 184–186 °C; IR
3
9
2.4, 116.2, 119.6, 120.7, 124.4, 127.4, 128.3, 128.7, 129.1, 130.3, 132.2,
–1
135.2, 138.5, 138.7, 145.4, 148.8, 149.2, 155.2, 195.6.
(KBr) (νmax/cm ): 2932, 2862, 1646, 1458, 1403, 1245, 1125, 756. Anal.

JOURNAL OF CHEMICAL RESEARCH 2017 383
calcd for C H ClNO : C, 75.09; H, 4.54; N, 3.50; found: C, 74.92; H,
5
6
7
8
9
S.C. Roy and P.K. Mandal, Tetrahedron, 1996, 52, 2193.
S.C. Roy and P.K. Mandal, Tetrahedron, 1996, 52, 12495.
Y.R. Lee, N.S. Kim and B.S. Kim, Tetrahedron Lett., 1997, 38, 5671.
M.C. Pirrung, J. Zhang and A.T. McPhail, J. Org. Chem., 1991, 56, 6269.
H.M.L. Davies, G. Ahmed, R.L. Calvo, M.R. Churchill and D.G. Churchill,
J. Org. Chem., 1998, 63, 2641.
2
5
18
2
1
4
2
1
4
.70; N, 3.64%. MS (m/z, %): 399 (10). H NMR (400 MHz, CDCl ): δ
3
.19 (s, CH , 3H), 5.08 (d, J = 5.2 Hz, CH, 1H), 5.98 (d, J = 5.4 Hz, CH,
3
13
H), 7.26–8.28 (m, 13H, arom). C NMR (100.6 MHz, CDCl ): δ 21.4,
3
6.2, 92.4, 116.2, 119.8, 120.7, 127.4, 128.1, 128.3, 128.7, 129.5, 130.2,
132.3, 135.2, 135.7, 138.6, 138.8, 140.2, 148.7, 155.4, 195.8.
10 M.C. Pirrung and F. Blume, J. Org. Chem., 1999, 64, 3642.
trans-3-(4-Bromophenyl)-2,3-dihydrofuro[3,2-h]quinolin-2-yl)
4-chlorophenyl)methanone (5l): Brown powder; m.p. 209–211 °C; IR
11 A.A. Jaxa-Chamiec and P.G. Sammes, J. Chem. Soc., Perkin Trans. 1,
1
980, 170.
12 H. Hagiwara, K. Sato, T. Suzuki and M. Ando, Tetrahedron Lett., 1997,
8, 2103.
(
(
–1
KBr) (νmax/cm ): 2919, 2821, 1644, 1402, 1260, 1024, 751, 535. Anal.
3
calcd for C H BrClNO : C, 62.03; H, 3.25; N, 3.01; found: C, 62.16;
2
4
15
2
13 S. Arai, K. Nakayama, Y. Suzuki, K. Hatano and T. Shioiri, Tetrahedron
Lett., 1998, 39, 9739.
1
H, 3.38; N, 3.17%. MS (m/z, %): 464 (7). H NMR (400 MHz, CDCl ):
3
δ 4.93 (J = 5.2 Hz, CH, 1H), 5.99 (J = 5.2 Hz, CH, 1H), 7.26–8.31 (m,
14 Y. Jiang and D. Ma, Tetrahedron: Asymmetry, 2002, 13, 1033.
15 W. Cao, W. Ding, J. Chen, Y. Chen, Q. Zang and G. Chen, Synth. Commun.,
13
1
3H, arom). C NMR (100.6 MHz, CDCl ): δ 45.8, 92.5, 116.2, 119.6,
3
2
004, 34, 1599.
120.6, 120.7 127.4, 128.3, 128.7, 130.2, 130.4, 132.1, 132.3, 135.2,
1
6
Z. Yang, M. Fan, R. Mu, W. Liu and Y. Liang, Tetrahedron, 2005, 61, 9140.
C.P. Chuang and A.I. Tsai, Synthesis, 2006, 675.
C.-J. Li and T.-H. Chan, Organic reactions in aqueous media. Wiley, New
York, 1997.
138.5, 138.7, 142.1, 148.8, 155.2, 195.3.
1
7
18
Received 30 March 2017; accepted 4 June 2017
Paper 1704676
https://doi.org/10.3184/174751917X14967701767058
Published online: 16 June 2017
19 C. Jiménez-González and D.J.C. Constable, Green chemistry and
engineering: A practical design approach. Wiley, Hoboken, 2011.
2
0
M. Salari, M.H. Mosslemin and A. Hassanabadi, J. Chem. Res., 2016, 40,
55.
M. Salari, M.H. Mosslemin and A. Hassanabadi, J. Chem. Res., 2017, 41,
0.
6
21
References
6
1
N.K. Terret, M. Gardner, D.W. Gordon, R.J. Kobylecki and J. Steel,
Tetrahedron, 1995, 51, 8135.
22 M. Salari, A. Hassanabadi and M.H. Mosslemin, J. Chem. Res., 2017, 41,
139.
2
F.M. Dean and M.V. Sargent, Comprehensive heterocyclic chemistry, eds
C.W. Bird and G.W.H. Cheeseman, Pergamon, Oxford, 1984, Vol. 4, chap.
23 M. Salari, A. Hassanabadi and M.H. Mosslemin, J. Chem. Res., 2017, 41,
271.
4
, p. 531.
24 A.T. Khan, M.S. Lal and R. Basha, Synthesis, 2013, 45, 406.
25 M. Anary-Abbasinejad, K. Charkhati and A. Hassanabadi, J. Chem. Res.,
2009, 2, 95.
3
4
B.H. Lipshutz, Chem. Rev., 1986, 86, 795.
V. Nair, J. Mathew and L.G. Nair, Synth. Commun., 1996, 26, 4531.