Amino oxazolines as easily accessible water stable ligands for palladium catalysed aqueous Heck reaction

Article abstract of DOI:10.3184/174751911X13100589976564

A series of amino oxazolinyl ligands were screened for palladium catalysed Heck reaction. These ligands work well as phosphine free system in aqueous, micellar medium, can be effectively recovered and reused for subsequent cycles.

Full text of DOI:10.3184/174751911X13100589976564

408 RESEARCH PAPER
JULY, 408–411
JOURNAL OF CHEMICAL RESEARCH 2011
Amino oxazolines as easily accessible water stable ligands for palladium
catalysed aqueous Heck reaction
Akeel S. Saiyed, Reshma S. Joshi and Ashutosh V. Bedekar*
Department of Chemistry, Faculty of Science, M. S. University of Baroda, Vadodara 390 002, India
A series of amino oxazolinyl ligands were screened for palladium catalysed Heck reaction. These ligands work well
as phosphine free system in aqueous, micellar medium, can be effectively recovered and reused for subsequent
cycles.
Keywords: amino oxazolines, water stable ligands, palladium, Heck reaction
Reaction of aryl halide and styrene with palladium catalyst
developed by Heck and Mizoroki1,2 remains an efficient option
for the synthesis of stilbene and its derivatives. A number of
different studies have been carried out to improve reaction
conditions, including ligands, solvents, bases and additives.3–5
Mostly the palladium salt is used in combination with phos-
phine ligand for this reaction. However, since the phosphine
ligands are often costly or difficult to prepare, there is an inter-
est to develop phosphine free conditions for this reaction.
Recently, some phosphine free Mizoroki–Heck reactions to
overcome some of these difficulties have been reported.6–8 In
this area mostly nitrogen based ligands are studied, some of
which are difficult to synthesise or are less effective. Oxazo-
line based ligands are easy to prepare, are stable in basic
medium and have been used in many catalytic reactions.9–11
Driven by environmental concerns, many efforts are being
made to develop this important reaction in aqueous medium.
Such reactions are generally carried out by using some addi-
tives. Generally surfactants, such as quaternary ammonium
salts, and cyclodextrins are used as additives.12–14 We now
report the synthesis and applications of amino oxazoline,
bis-oxazoline ligands and their use in Mizorok–Heck reaction
in aqueous medium.
excellent yield with respectable TON of 9300. [Turn Over
Number (TON) = moles of product formed/moles of catalyst
used]. The catalytic cycle of the Heck reaction starts with
reduction of Pd(II) to Pd(0), often referred as preactivation,
followed by oxidative addition of arylhalide, insertion of olefin
and finally reductive elimination.17–19 In the case of phosphine
free reaction conditions, the initial reduction of palladium
during preactivation is assisted by nucleophilic amines of the
ligands (see Scheme 2 and Table 1).
In this research we have also developed reaction conditions
for phosphine free ligand mediated Pd catalysed Mizorok–
Heck reaction in water as part of solvent system. Initially
the reaction was carried out in aqueous mixture of DMA in
different proportions in order to solubilise the substrates. The
presence of surfactants can help to dissolve water insoluble
molecules in aqueous systems via their stabilisation in micellar
system. We investigated the use of cetyltrimethylammonium
bromide (CTAB) at concentrations higher than CMC for our
catalytic Heck reaction in pure water. This reduces the use
of DMA as a co-solvent in the reaction and may offer a green
method for this conversion.
Conditions were optimised for the use of amino oxazoline
ligands 1 and 2 in DMA for the Heck reaction with excellent
conversions and high TON; several examples are shown in
Table 2.
At the same time we also developed same reaction in
mixture of DMA–water and then in pure water with CTAB and
results are presented in Tables 3 and 4.
Generally, the disadvantage of homogeneous system is its
inability to reuse the catalyst, usually this is overcome for the
Mizoroki-–Heckby using heterogeneous palladium catalysts.16
Alternatively, this deficiency may be addressed if the catalyst
Results and discussion
The ligands 1, 2 are prepared from isatoic anhydride while 3
from 1,2-dicyanobenzene and amino alcohol in presence of
suitable Lewis acid15 such as ZnCl2 or clay (Scheme 1).
The ligands were tested for the standard reaction of iodo-
benzene 6 and styrene 7 (1.5 equiv.) with Pd(OAc)2 (0.1%),
ligand 1 to 5 (0.25%), K2CO3 (2 eq.) in DMF at 140 °C for
40 h. The product, trans-stilbene 7 was isolated respectively
for ligand 1 (88%), 2 (95%), 3 (92%), 4 (28%) and 5 (92%).
The oxazolinyl N,N-ligands 1 to 3 are comparable to bis-
phosphine ligand dppp, 5. The solvents DMF, DMA or NMP
worked almost equally while further optimization showed that
ligand 1 or 2 (0.025%) with Pd(OAc)2 (0.01%) for the same
reaction with TBAB (25%) in DMA gave trans-stilbene in
Scheme 2 Standard Heck reaction.
Scheme 1 Ligands screened for Heck reaction.
* Correspondent. E-mail: avbedekar@yahoo.co.in

JOURNAL OF CHEMICAL RESEARCH 2011 409
Table 1 Optimisation of reaction conditions for Mizoroki–Heck reaction
No.
Aryl halide 1 equiv. Pd(OAc)2/mol %
Ligand 1 /mol %
Solvent (DMA:H2O)
Yielda/% [TON]
Additive
1
2
Iodobenzene
Iodobenzene
Iodobenzene
Iodobenzene
Iodobenzene
Iodobenzene
Iodobenzene
Iodobenzene
Bromobenzene
Bromobenzene
Iodobenzene
Iodobenzene
0.01
1
0.025
2.5
1:0
1:2
1:2
1:2
1:2
1:2
1:2
1:2
1:2
1:2
0:1
0:1
93 [9300]
98 [98]
TBAB (0.25 equiv.)
--
3
0.1
0.25
0.0125
0.25
1.25
1.25
1.25
1.25
1.25
1.25
1.25
86 [863]
91 [18163]
98 [977]
90 [180]
86 [172]
87 [174]
34 [68]
66 [132]
86 [172]
52 [104]
--
4
0.005
0.1 (PdCl2)
0.5
--
5
--
6
--
7
0.5
CTAB (0.1 equiv.)
CTAB (0.1 equiv.)
--
8
0.5
9
0.5
11
12
13
0.5
TBAB (0.1 equiv.)
CTAB (0.1 equiv.)
--
0.5
0.5
All reactions with styrene (1.5 equiv.), K2CO3 (2 equiv.), at 140 °C for 40 h.
a Isolated.
Table 2 Screening the present catalyst system for Mizoroki-Heck reaction for various examples in DMA
No
Aryl halide
Product
Yield/%a
1
2
3
4
5
6
4-Iodoanisole (9)
4-Methoxystilbene (10)
4-Nitrostilbene (12)
3-Styrylphenanthrene (14)
2-Styrylbenzo[c]phenanthrene(16)
2-Styrylnaphthalene (18)
tert-Butylcinnamate (20)
79
82
95
95
88
80
4-Bromonitrobenzene (11)
3-Bromophenanthrene (13)
2-Bromobenzo[c]phenanthrene (15)
2-Bromonaphthalene (17)
Iodobenzene (19)
Entry 1–5 with styrene (1.5 equiv.) and 6 with tert-butyl acrylate (1.5 equiv.), K2CO3 (2 equiv.), Pd(OAc)2 (1.0%), 1 or 2 (1.25%) in DMA
at 140 °C for 40 h.
a Isolated.
Table 3 Investigating the present system for Mizoroki-Heck reaction with DMA-water (1:2)
No
Aryl halide
Product
Yield/%a
[TON]b
1
2
3
4
4-Iodoanisole (9)
4-Methoxystilbene (10)
4-Nitrostilbene (12)
89
[179]
64
[127]
90
[180]
58
[58]
4-Bromonitrobenzene (11)
3-Bromonitrobenzene (21)
1,2-Dibromobenzene(23)
3-Nitrostilbene (22)
1,2-Distyrylbenzene (24)
Entry 1–3 with styrene (1.5 equiv.), K2CO3 (2 equiv.), Pd(OAc)2 (0.5%), 1 (1.25%) and entry 4 with styrene (3.0 equiv.), K2CO3 (4 equiv.),
Pd(OAc)2 (1.0%), 1 (2.5%). All reactions with DMA–water (1:2), 120 °C, for 40 h, TBAB (10% for entries 1–3 and 20% for entry 4).
a Isolated, b TON= Turn Over Number = moles of product formed/moles of catalyst used.
Table 4 Examples of Mizoroki–Heck reaction in water–CTAB system
No.
Ar–X
Olefin (1.5 equiv.)
Product
Yielda/% [TON]b
1
2
3
4
5
6
Iodobenzene
Styrene
8
25
26
10
27
28
87 [174]
88 [176]
94 [186]
82 [172]
95 [190]
71 [141]
Iodobenzene
4-Methylstyrene
4-Vinylpyridine (1.2 equiv.)
Styrene
Iodobenzene
4-Iodoanisole
4-Iodoanisole
4-Bromochlorobenzene
4-Methylstyrene
Styrene
All reactions with ligand Pd(OAc)2 (0.5%), 1 (1.25%), K2CO3 (2.0 equiv.), at 140 °C for 40 h.
a Isolated. b TON= Turn Over Number = moles of product formed/moles of catalyst used.
can be recovered and reused for the next set of reactions. Since
the product of the standard Heck reaction is stilbene, which
can be extracted in non polar solvent such as petroleum ether,
the catalyst/ligand may remain in the aqueous portion and may
be recycled. Accordingly, a separate set of experiment was run,
the product stilbene extracted and aqueous system used as such
for the second cycle. The yields of first and second cycles were
comparable (88 and 84%); however, there was a drop in the
third cycle (60%) probably due to slight solubility of CTAB in
petroleum ether. In order to check this, half of the original
quantity of CTAB was added in the fourth cycle. The yield was
increased substantially (73%).
Thus we have demonstrated that the present phosphine free
catalyst system not only works well in water–CTAB or water–
DMA solvent but it can be recovered and reused effectively for
subsequent reactions.

410 JOURNAL OF CHEMICAL RESEARCH 2011
extracted with dichloromethane (3 × 30 mL). The organic layer was
washed with water (2 × 20 mL) and dried over anhydrous sodium
sulfate. The solution was concentrated under reduced pressure to
obtain a viscous liquid, which was purified by column chromatogra-
phy on silica gel and petroleum ether as eluent to give pure stilbene as
white solid (0.178 g, 79%).
Experimental
2-(4,4-Dimethyl-4,5-dihydrooxazol-2-yl)phenylamine (1): In a 100-
mL two-necked flask, anhydrous zinc chloride (0.042 g, 0.306 mmol,
10 mol %) was prepared by melting it under high vacuum. After cool-
ing to room temperature under nitrogen, dry chlorobenzene (10 mL),
isatoic anhydride (0.50 g, 3.06 mmol) and 2-amino-2-methylpropan-1-
ol (0.41 g, 4.60 mmol) were charged to this flask under nitrogen. The
mixture was refluxed for 24 h. The solvent was removed under reduced
pressure and the oily residue was dissolved in dichloromethane
(25–30 mL). The solution was washed three times with water (3 ×
20 mL) and the aqueous phase was extracted again with dichlorometh-
ane (2 × 20 mL). The combined organic phase was dried with anhy-
drous sodium sulfate and the solvent was removed in a vacuum. The
resulting oil was purified by column chromatography on neutral alu-
mina using light petroleum ether as eluent to afford 1 (0.455 g; 78%)
as a white solid; m.p.103–106 °C (lit.15104–106 °C). 1H NMR (CDCl3,
400 MHz) δ 1.37 (s, 6 H), 4.00 (s, 2 H), 5.81 (s, 2 H), 6.63–6.69 (m,
2 H), 7.17–7.21 (m, 1 H), 7.67–7.70 (dd, J = 8.0 and 1.6 Hz, 1 H).
IR (KBr) υ 3445, 3284, 3032, 2962, 1381, 1331, 1186, 754 cm−1.
Benzyl-[2(4,4-dimethyl-4,5-dihydrooxazol-2-yl)phenyl]amine (2):
In a 100-mL two-necked flask, anhydrous zinc chloride (0.054 g,
0.395 mmol, 10 mol %) was prepared by melting it under high vacuum.
After cooling to room temperature under nitrogen, dry chlorobenzene
(10 mL), 1-benzyl-1H-benzo[d][1,3]oxazine-2,4-dione (1.0 g, 3.95
mmol) and 2-amino-2-methylpropan-1-ol (0.527 g, 5.92 mmol) were
mixed under nitrogen. The mixture was refluxed for 24 h. The solvent
was removed under reduced pressure and the oily residue was dis-
solved in dichloromethane (25–30 mL). The solution was washed
three times with water (3 × 20 mL) and the aqueous phase was
extracted again with dichloromethane (2 × 20 mL). The combined
organic phase was dried with anhydrous sodium sulfate and the
solvent was removed in a vacuum. The resulting oil was purified by
column chromatography on neutral alumina using light petroleum
ether as eluent to afford 2 (0.421 g; 72%) as a white solid. 0.792 g
Using the general procedure following stilbenes were synthesised
utilising appropriate styrene derivatives:
4-Methoxystilbene (10): White solid; m.p. 134–135 °C (lit.20 135–
136 °C). 1H NMR: (CDCl3, 400 MHz) δ 3.83 (s, 3H), 6.89–6.91 (m,
2H), 6.95–6.99 (d, J = 16.3 Hz, 1H), 7.05–7.09 (d, J = 16.2 Hz, 1H),
7.23–7.25 (m, 1H), 7.32–7.36 (m, 2H), 7.44–7.50 (m, 4 H). IR (KBr)
υ 3002, 2853, 1641, 1511, 1446, 1384, 1296, 1179 cm.−1 MS (EI)
(m/z): 210 (M+, 100), 179 (14), 167 (27), 105 (7), 76(3).
4-Nitrostilbene (12): Yellow solid; m.p.159–160 °C (lit.21 157 °C).
1H NMR (CDCl3, 400 MHz) δ 7.16–7.12 (d, J = 16.3 Hz, 1H), 7.3–
7.26 (d, J = 16.3 Hz, 1H), 7.31–7.33 (m, 2H), 7.36–7.42 (m, 2H),
7.58–7.60 (m, 2H), 7.60–7.90 (m, 2H), 8.73–8.75 (d, J = 9.2 Hz, 1H).
IR (KBr) υ 2922, 1590, 1340, 1107, 970, 694 cm.−1 MS (EI) (m/z): 225
(M+, 100), 179 (43), 167 (8.9), 89 (12.5), 77(5.86).
tert-Butyl cinnamate (20): Colourless liquid.22 1H NMR (CDCl3,
400 MHz) δ 1.53 (s, 9H), 6.35–6.39 (d, J = 16.0 Hz, 1H), 7.35–7.37
(m, 3H), 7.49–7.52 (m, 2H), 7.56–7.60 (d, J = 16.0 Hz, 1H). IR (neat)
υ 2978, 1711, 1635, 1578, 1496, 1475, 1450, 1392, 1367, 1328, 1257,
1207, 1150 cm−1.
3-Styrylphenanthrene (14): White solid; m.p. 152–154 °C (lit.23
154 °C). 1H NMR (CDCl3, 400 MHz) δ 7.30–7.36 (m, 2H), 7.40–7.45
(m, 3H), 7.62–7.65 (m, 3H), 7.68–7.75 (m, 3H), 7.85–7.93 (m, 3H),
8.76 (s, 1H), 8.77–8.78 (d, J = 4.4 Hz, 1H). IR (KBr) υ 3023, 1595,
1487, 1109, 1034, 940, 771, 738 cm−1. MS (EI) (m/z): 281 (M+1, 22.6),
280 (M+, 100), 263 (8.7), 140 (19).
2-Styrylbenzo[c]phenanthrene (16): White solid: m.p. 142 °C (lit.24
140 °C). 1H NMR (CDCl3, 400 MHz) δ 7.28–7.35 (m, 3H), 7.41–7.45
(m, 3H), 7.63–7.69 (m, 3H), 7.43–7.78 (m, 1H), 7.81–7.86 (m, 2H),
7.89–7.94 (m, 3H), 8.04–8.07 (m, 2H), 9.18 (s, 1H), 9.18–9.20 (d, J =
3.6 Hz, 1H). IR (KBr) υ 3017, 1600, 1499, 1072, 1043, 982, 902, 782,
744 cm.−1 MS (EI) (m/z): 331 (M+1, 28), 330 (M+, 100), 226 (12.3),
164 (23.6).
1
(72%) of a clean product; m.p. 80 °C. H NMR: (CDCl3, 400 MHz)
δ 1.36 (s, 6 H), 4.01 (s, 2 H), 4.51 (s, 2 H), 6.59–6.62 (t, J = 14.2 Hz
and 5.9 Hz, 2 H), 7.19–7.25 (m, 2H), 7.37–7.30 (m, 4 H), 7.74–7.76
(d, J = 7.4 Hz, 1 H), 8.96 (bs, 1H). IR (KBr) υ 3262, 2963, 1918, 1811,
1628, 1384, 1089, 925, 840, 766 cm.−1 Elemental Anal. Calcd for
C18H20N2O: C, 77.11; H, 7.18; N, 9.99. Found C, 77.12; H, 7.36;
N, 10.02%.
1,2-Bis(4,4-dimethyl-2-oxazolin-2-yl)benzene (3): A mixture of
anhydrous zinc chloride (0.06 g, 0.39 mmol, 10 mol %), 1,2-dicy-
anobenzene (0.5 g, 3.87 mmol) and 2-amino-2-methylpropan-1-ol
(1.04 g, 11.7 mmol) in chlorobenzene (5 mL) was heated under nitro-
gen at 120 °C for 24 h. The solvent was removed under reduced pres-
sure and the oily residue was dissolved dichloromethane. The solution
was washed with water and the aqueous phase was again extracted
with dichloromethane. The combined organic phase was dried with
sodium sulfate and the solvent was removed in vacuum. The resulting
oil was purified by column chromatography on neutral alumina using
2-Styrylnaphthalene (18): White solid; m. p. 146–147 °C (lit.25
147–149 °C). 1H NMR (CDCl3, 400 MHz) δ 7.24–7.30 (m, 3H), 7.34–
7.40 (m, 2H), 7.42–7.49 (m, 2H), 7.55–7.57 (dd, J = 8.6 and 1.3 Hz,
2H), 7.73–7.75 (dd, J = 8.6 and 1.3 Hz, 1H), 7.77–7.85 (m, 4H). IR
(KBr) υ 3077, 3045, 1595, 1510, 1496, 1448, 1350, 1074, 957, 794,
775 cm−1. MS (EI) (m/z): 230 (M+, 100), 215 (21), 115 (15),
107 (9.1).
Synthesis of trans-stilbene (8) (with CTAB in water)
Catalyst solution: A solution of palladium acetate (0.0014 g,
0.006 mmol/0.5 mol %) and 1 (0.0029 g, 0.0153 mmol/1.25 mol %)
was prepared in 5 mL water. The mixture was sonicated in ultrasonic
water bath for 5 min.
In another two-neck round bottom flask iodobenzene (6) (0.250 g,
1.2 mmol),K2CO3 (0.338 g,2.45 mmol),CTAB(0.045 g,0.123 mmol)
in water 5 mL were mixed. Then the solution was heated up to 60 °C,
and styrene (0.19 g, 1.838 mmol) was added. After 15 mins tempera-
ture was raised to 90 °C, and to this the previously prepared catalyst
solution was added at once. The combined reaction mixture was
heated to 100 °C for 40 h. The cooled mixture was poured in 6N HCl
and extracted with dichloromethane (3 × 40 mL). The organic layer
was washed with water and dried over Na2SO4, concentrated under
reduced pressure. The product was purified by column chromatogra-
phy using silica gel and petroleum ether as eluent. White crystals,
0.192 g (86%), m.p. 120–122 °C (lit. 29 121–123 °C).
(E)-3-Nitrostilbene (22): Pale yellow crystals; m.p. 108–110 °C
(lit.26 111–112 °C). 1H NMR (DMSO, 400 MHz) δ 7.31–7.34 (m, 1H),
7.40–7.53 (m, 4H), 7.66–7.70 (m, 3H), 8.07–8.12 (m, 2H), 8.44
(s, 1H). IR (KBr) υ 2925, 1588, 1355, 1117, 980, 714 cm−1. MS (EI)
(m/z): 225 (M+, 60), 178 (100), 152 (23), 76(12).
30
petroleum ether as eluent to afford 3 as pale yellow oil (0.638 g,
60%). 1H NMR (CDCl3, 400 Hz) δ 1.39 (s, 12H), 4.07 (s, 2H), 7.45–
7.48 (m, 2H), 7.74–7.76 (m, 2H). IR (KBr) υ 3068, 2968, 1651, 1599,
1493, 1383, 1249, 1189, 1080, 989, 921, 864, 776, 689 cm−1.
Typical procedure for the Heck reaction
Catalyst solution (entry 1, Table 1): In a typical procedure, a catalyst
solution was separately prepared in an oven dry, N2 flushed two-neck
round bottomed flask. A solution of palladium acetate (1.2 mg,
0.0055 mmol, 0.5 mol %) and ligand 1 (2.6 mg, 0.0137 mmol,
1.25 mol %) was prepared in dry N,N-dimethylacetamide (5 mL),
under N2 atmosphere. The mixture was stirred at room temperature
until homogeneous (about 15 min) and degassed several times prior
to use.
A mixture of 4-iodoanisole (0.250 g, 1.1 mmol), dry K2CO3
(0.297 g, 2.20 mol) in dry N,N-dimethylacetamide (5 mL) was repeat-
edly degassed by purging with N2 gas. The solution was heated to
60 °C and styrene (0.172 g, 1.65 mol) was slowly added. After the
addition, the temperature was increased (100 °C) and previously
prepared palladium catalyst solution was added dropwise and the
reaction mixture heated to 140 5 °C for 40 h. The cooled mixture
was then poured in water (25 mL) containing 6N HCl (5 mL) and
1,2-Distyrylbenzene (24): Pale yellow crystals; m.p.115 °C (lit.27
111–112 °C). 1H NMR (CDCl3, 400 MHz) δ 6.98–7.02 (d, J = 16.4 Hz,
2H), 7.24–7.30 (m, 4H), 7.34–7.38 (m, 4H), 7.44–7.48 (d, J = 16.4 Hz,
2H), 7.51–7.54 (m, 4H), 7.58–7.60 (m, 2H). IR (KBr) υ 3086, 3053,
3019, 1600, 1491, 1213, 1158, 1071, 956, 758, 691 cm−1. MS (EI)
(m/z): 223 (M+1, 8.9), 282 (M+, 38), 191 (100), 178(5.6), 91 (12.3).

JOURNAL OF CHEMICAL RESEARCH 2011 411
(E)-4-Methylstilbene (25): White solid; m.p. 112–114 °C (lit.28
114–116 °C). 1H NMR (CDCl3, 400 MHz) δ 2.38 (S, 3H), 7.06–7.10
(d, J = 16.2 Hz, 1H), 7.10–7.14 (d, J = 16.2 Hz, 1H), 7.19–7.21 (d,
J = 8 Hz, 2H), 7.25–7.29 (m, 1H), 7.36–7.40 (m, 2H), 7.43–7.45 (d,
J = 8 Hz, 2H), 7.52–7.54 (m, 2H). IR (KBr) υ 2925, 1588, 1355, 1117,
980, 714 cm−1. MS (EI) (m/z): 195 (M+, 93.5), 179 (100), 89 (11),
76 (5.3).
Received 16 April 2011; accepted 30 June 2011
Paper 1100664 doi: 10.3184/174751911X13100589976564
Published online: 5 August 2011
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(E)-4-Chlorostilbene (28): White solid; m.p. 130 °C (lit.28 129–
1
130 °C). H NMR (CDCl3, 400 MHz) δ 7.04–7.08 (d, J = 16.2 Hz,
1H), 7.09–7.13 (d, J = 16.2 Hz, 1H), 7.29–7.47 (m, 5H), 7.44–7.47
(m, 2H), 7.52–7.54 (m, 2H). IR (KBr) υ 2925, 1588, 1355, 1117, 980,
714 cm−1. MS (EI) (m/z): 214 (M+, 80), 179 (100), 89 (33), 76 (20).
Synthesis of trans-stilbene (8) (recycle experiment)
Catalyst solution: A solution of palladium acetate (0.0014 g,
0.0613 mmol/0.5 mol %) and 1 (0.0029 g, 0.0153 mmol/1.25 mol %)
was prepared in water (5 mL). The mixture was sonicated in ultrasonic
water bath for 5 min.
In another two-neck round bottomed flask iodobenzene (6) (0.250 g,
1.2 mmol), K2CO3 (0.338 g, 2.45 mmol), CTAB (0.045 g, 0.123 mmol)
in water (5 mL) were mixed. Then the solution was heated up to
60 °C, and styrene (0.19 g, 1.84 mmol) was added. After 15 mins
temperature was raised to 90 °C, and to this mixture the previously
prepared catalyst solution was added at once. The combined reaction
mixture was heated to 100 °C for 40 h. The cooled mixture was poured
in water (10 mL), extracted with petroleum ether (40 mL) for 7 to
8 times (till complete removal of product from aqueous layer, as
indicated by TLC). The combined organic layer was washed with
water and dried over anhydrous Na2SO4, concentrated under reduced
pressure. The product was purified by column chromatography using
silica gel and petroleum ether as eluent. The aqueous layer was
collected in another round bottomed flask quantitatively which con-
tain catalyst solution. To this solution all the other starting materials
for next cycle were added and the reaction was conducted. The same
procedure was employed for the recycle study.
We would like to thank Gujarat Narmada Fertilizer Corpora-
tion (GNFC), Bharuch for the financial support and Prof.
B.V. Kamath for the laboratory facilities and constant
encouragement.
31 N. Romain, C. K. Jin, A.F. Coffey, J.W. Davies and M. Bradley Chem.
Commun., 2007, 5031.

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