Green syntheses of n-alkyl-2-styrylbenzimidazoles

Article abstract of DOI:10.14233/ajchem.2013.15080

Simple and green methodologies for the syntheses of 2-styrylbenzimidazoles (3a-c) and its N-alkyl derivatives (7a-i) have been developed. o-Phenylenediamine (1) was condensed with cinnamic acids (2a-c) resulting in 2-styrylbenzimidazoles (3a-c) using glycerol as a green and efficient solvent. 3 were also prepared alternatively by the condensation of 2-methylbenzimidazole (4) with benzaldehydes (5a-c) using glycerol as solvent. 2-Styrylbenzimidazoles (3a-c) and 2-methylbenzimidazole (4) were alkylated independently to obtain N-alkyl- 2-styrylbenzimidazole (7a-i) and N-alkyl-2-methylbenzimidazole (6a-c), respectively using DMS/DES/PhCH2Cl applying green methods such as simple physical grinding of reactants in solid phase, treating reactants in PEG-600 as a solvent in solution phase and using microwave irradiation of reactants respectively. Compounds 7a-i could also be prepared, alternatively, by heating 6a-c with 5a-c in glycerol at 180 °C for 3-4 h.

Full text of DOI:10.14233/ajchem.2013.15080

Asian Journal of Chemistry; Vol. 25, No. 17 (2013), 9569-9572
http://dx.doi.org/10.14233/ajchem.2013.15080
Green Syntheses of N-Alkyl-2-styrylbenzimidazoles
*
T. ASHOK KUMAR , B. RAMA DEVI and P.K. DUBEY
Department of Chemistry, Jawaharlal Nehru Technological University Hyderabad, College of Engineering, Kukatpally, Hyderabad-500 085,
India
*Corresponding author: E-mail: ashok.jntu@gmail.com
(Received: 2 January 2013;
Accepted: 4 October 2013)
AJC-14231
Simple and green methodologies for the syntheses of 2-styrylbenzimidazoles (3a-c) and its N-alkyl derivatives (7a-i) have been developed.
o-Phenylenediamine (1) was condensed with cinnamic acids (2a-c) resulting in 2-styrylbenzimidazoles (3a-c) using glycerol as a green
and efficient solvent. 3 were also prepared alternatively by the condensation of 2-methylbenzimidazole (4) with benzaldehydes (5a-c)
using glycerol as solvent. 2-Styrylbenzimidazoles (3a-c) and 2-methylbenzimidazole (4) were alkylated independently to obtain N-alkyl-
2-styrylbenzimidazole (7a-i) and N-alkyl-2-methylbenzimidazole (6a-c), respectively using DMS/DES/PhCH2Cl applying green methods
such as simple physical grinding of reactants in solid phase, treating reactants in PEG-600 as a solvent in solution phase and using
microwave irradiation of reactants respectively. Compounds 7a-i could also be prepared, alternatively, by heating 6a-c with 5a-c in
glycerol at 180 °C for 3-4 h.
Key Words: 2-Styrylbenzimidazoles, Glycerol, Alkylations, Physical grinding, Microwave irradiation, PEG-600.
being used. Melting points were determined using a Buchi
Melting Point B-545 apparatus and are uncorrected. TLC
analyses were done on glass plates coated with silica gel GF-
254 and spotting was done using iodine/UV lamp. IR spectra
were recorded on a Perkin-Elmer model 446 instrument in
INTRODUCTION
The development of green methods for syntheses of target
compounds from easily available starting materials is a major
challenge to the present day organic chemist. In this category,
glycerol mediated1-3 reactions are very useful for the synthesis
of important heterocycles such as benzimidazoles which are
known to possess a range of biological activities such as anti-
hypertensive4, antiviral4 and anticancer types5. Compounds that
contain benzimidazole skeleton exhibit significant activity
against several viruses such as HIV6, herpes simplex virus
Type-1 (HSV-1)7, influenza8 and human cytomegalovirus
(HCMV)6.
1
KBr phase. H NMR were recorded in CDCl3/DMSO using
400 MHz Varian Gemini spectrometer and mass spectra were
recorded on LC-MS spectrometer, model HP-5989A.
Preparation of 2-styrylbenzimidazoles (3a-c) from o-
phenylenediamine (1): An intimate mixture of 1 (1.08 g,
10 mM), cinnamic acids (2a-c) (10 mM) and glycerol (10 mL)
was heated at 170-180 °C for 1 h.At the end of this period, the
reaction mixture was poured into ice cold water. The separated
solid was filtered, washed with water and dried. The crude
products were recrystallized from suitable solvent to get pure
3a-c.
Although many methods are available for the synthesis
of 2-substituted benzimidazoles9-16, not much work seems to
have been done to develop green synthetic methods to prepare
these types of compounds. Among the most notable green
methods used in synthesis, solid phase synthesis17,18, solution
phase synthesis using green solvents19 and microwave tech-
niques20 are very important. In continuation of our earlier work
on synthesis of 2-styrylbenzimidazoles21-24, we now wish to
report our studies on preparation and N-alkylation of 2-styryl-
benzimidazoles using green methodologies.
Alternative preparation of 2-styrylbenzimidazoles (3a-
c) from 2-methylbenzimidazole (4): A mixture of 4 (1.32 g,
10 mM), aromatic aldehydes (5a-c) (10 mM) and glycerol
(10 mL) was heated at 170-180 °C for 3 h in an oil bath.At the
end of this period, the reaction mixture was cooled to room
temperature, dissolved in isopropanol (25 mL) and treated with
a solution of oxalic acid (1.5 g) in isopropanol (10 mL). Each
of the oxalate salts of (3a-c) obtained were filtered and
neutralized, independently, with aqueous NH3 to pH of 8-10.
The products were filtered, washed with water, dried and
recrystallized using suitable solvent to obtain 3a-c.
EXPERIMENTAL
All the reagents used in this work were obtained from
commercial suppliers. Solvents were freshly distilled before

9570 Kumar et al.
Asian J. Chem.
Preparation of N-alkyl-2-styrylbenzimidazoles (7a-i)
1-Methyl-2-(2-p-tolyl-vinyl)-1H-benzimidazole (7d)
(Table-1, entry 7):Yield (1.8 g, 72 %), m.p. 129-130 °C (Lit.
m.p.24 128-130), IR (KBr, νmax, cm-1): 3010 (-CH=CH),
from N-alkyl-2-methylbenzimidazoles [6(a-c)]:The procedure
is same as mentioned above for the synthesis of 3a-c from 4.
Preparation of N-alkyl-2-styrylbenzimidazoles (7a-i)
& N-alkyl-2-methylbenzimidazoles [6(a-c)]: In solid phase
(Physical grinding method). A mixture of 3a-c or 4 (10 mM),
K2CO3 (20 mM), tetrabutylammonium bromide (1 mM) and
alkylating agent (10 mM) were ground together independently
for about 10-15 min in a mortar with a pestle at room tempe-
rature to obtain a homogeneous mixture. The latter was then
treated with ice-cold water (30-40 mL). The separated solid
was filtered, washed with water (2 × 10 mL) and dried to obtain
crude 6a-c or 7a-i respectively, which were recrystallized from
a suitable solvent to obtain pure 7a-i or 6a-c respectively. For
yields (Table-2).
1
1625(C=N), H NMR (400 MHz, DMSO-d6): δ 2.3 (3H, s,
-CH), δ 3.6 (3H, s, N-CH), δ 6.9-7.0 (2H, dd, trans-CH=CH),
d 7.0-7.2 (4H, q, aromatic), δ 7.3-7.7 (4H, m, aromatic), MS:
m/z 249.13 (M+). Anal. calcd. (%) for C17H16N2: C, 82.22; H,
6.49; N, 11.28; Found C, 82.30; H, 6.55; N, 11.30.
1-Ethyl-2-(2-p-tolyl-vinyl)-1H-benzimidazole (7e)
(Table-1, entry 8): Yield (1.8 g, 70 %), m.p. 108-110 °C, IR
(KBr, νmax, cm-1): 3010 (-CH=CH), 1625 (C=N), 1H NMR (400
MHz, DMSO-d6): δ 1.5 (3H, t, N-C-CH), δ 2.3-2.5 (3H, s,
-CH), δ 3.7-3.8 (2H, q, N-CH), δ 6.9-7.0 (2H, dd, trans-
CH=CH), δ 7.0-7.2 (4H, q, aromatic) δ 7.3-7.7 (4H, m, aromatic);
MS: m/z 263. 35(M+).Anal. calcd. (%) for C18H18N2: C, 82.41;
H, 6.92; N, 10.68; Found C, 82.44; H, 6.98; N, 10.80.
N-Benzyl-2-(2-p-tolyl-vinyl)-1H-benzimidazole (7f)
(Table-1, entry 9): Yield (2.1 g, 65 %), m.p. 210-212 °C, IR
(KBr, νmax, cm-1): 3020 (-CH=CH), 1624(C=N), 1H NMR (400
MHz, DMSO-d6): δ 2.3-2.5 (3H, s, -CH), δ 4.9-5.0 (2H, s,
N-CH), δ 6.9-7.0 (2H, dd, trans-CH=CH), δ 7.0-7.2 (9H, m,
aromatic), δ 7.3-7.7 (4H, m, aromatic) ; MS: m/z 325.12 (M+).
Anal. calcd. (%) for C23H20N2: C, 85.15; H, 6.21; N, 8.63;
Found C, 85.24; H, 6.28; N, 8.72.
In solution phase (In PEG-600): A mixture of 3a-c or 4
(10 mM), alkylating agent (10 mM) and PEG-600 (20 mL)
were taken to heat at 100 °C on water bath for 2 h. At the end
of this period, the reaction mixture was poured into ice-cold
water. The separated solid was filtered, washed with water and
dried. The crude products were recrystallized from suitable solvent
to obtain pure 7a-i or 6a-c respectively. For yields (Table-3).
Under microwave irradiation condition: A mixture of
3a-c or 4 (10 mM) dissolved in PEG-600 (10 mL) and alky-
lating agent (10 mM) was added and taken in a 10 mL CEM-
reaction tube sealed by rubber stopper and subjected to
microwave irradiation for 5 min at 130 °C in the commercial
micro-wave reactor. After that, the tube was cooled and the
completion of reaction was checked by TLC then poured into
ice-cold water. The separated solid was filtered, washed with
water and dried. The crude product was recrystallized from a
suitable solvent to obtain pure 7a-i or 6a-c respectively. For
yields (Table-4).
2-[2-(4-Chloro-phenyl)-vinyl]-1-methyl-1H-benzimi-
dazole (7g) (Table-1, entry 10): Yield (1.9 g, 73 %), m.p.
143-145 °C (Lit. m.p.24 142-143 °C), IR (KBr, νmax, cm-1): 3010
(-CH=CH), 1625 (C=N), 1H NMR (400 MHz, DMSO-d6): δ
3.6 (3H, s, N-CH), δ 6.9-7.0 (dd, 2H, trans-CH=CH), δ 7.3-
7.8 (8H, m, aromatic); MS: m/z 269 (M+). Anal. calcd. (%) for
C16H13N2Cl: C, 71.51; H, 4.88; Cl, 13.19; N, 10.42; Found C,
71.60; H, 4.92; Cl, 13.30; N, 10.55.
2-[2-(4-Chloro-phenyl)-vinyl]-1-ethyl-1H-benzimida-
zole (7h) (Table-1, entry 11): Yield (1.9 g, 70 %), m.p. 136-
138 °C, IR (KBr, νmax, cm-1): 3010 (-CH=CH), 1624 (C=N),
1H NMR (400 MHz, DMSO-d6): δ 1.5 (3H, t, N-C-CH), δ 3.7-
3.8 (2H, q, N-CH), δ 6.9-7.0 (2H, dd, trans-CH=CH), δ 7.2-
7.8 (8H, m, aromatic); MS: m/z 283.7 (M+). Anal. calcd. (%)
for C17H15N2Cl: C, 72.21; H, 5.35; Cl, 12.54; N, 9.91; Found
C, 72.30; H, 5.42; N.9.99.
Physical and spectral data of the obtained compounds are
given below.
1-Methyl-2-styryl-1H-benzimidazole (7a) (Table-1,
entry 4): Yield (1.6g, 70 %), m.p. 114-115 °C (Lit. m.p.24
112-114), IR (KBr, νmax, cm-1): 3010 (-CH=CH), 1624 (C=N),
1H NMR (400 MHz, DMSO-d6): δ 3.6 (3H, s, -N-CH), δ 6.9-
7.0 (2H, dd, trans-CH=CH), δ 7.1-7.3 (5H, m, aromatic) δ
7.2-7.7 (4H, m, aromatic); MS: m/z 249.13 (M+). Anal. calcd.
(%) for C16H14N2: C, 82.02; H, 6.02; N, 11.96; Found C, 82.12;
H, 6.10; N, 11.99.
N-Benzyl-2-[(E)-2-(4-chlorophenyl)ethenyl]-1H-1,3-
benzimidazole (7i). (Table-1, entry 12):Yield (2.4 g, 72 %),
m.p. > 230 °C, IR (KBr, νmax, cm-1): 3020 (-CH=CH), 1625
(C=N), 1H NMR (400 MHz, DMSO-d6): δ 4.9-5.0 (2H, s, N-
CH), δ 6.9-7.0 (2H, dd, trans-CH=CH), d 7.0-7.2 (5H, m, aro-
matic), δ 7.3-7.8 (8H, m, aromatic); MS: m/z 345.42 (M+).
Anal. calcd. (%) for C22H17N2Cl: C, 76.63; H, 4.97; Cl, 10.28;
N, 8.12; Found C, 76.70; H, 4.99; Cl, 10.35; N, 8.26.
1-Ethyl-2-styryl-1H-benzimidazole (7b) (Table-1, en-
try 5): Yield (1.6 g, 68 %), m.p. 158-160 °C (Lit. m.p.24 160-
161 °C), IR (KBr, νmax, cm-1): 3010 (-CH=CH), 1625 (C=N),
1H NMR (400 MHz, DMSO-d6): δ 1.5 (3H, t, N-C-CH), δ 3.7-
3.8 (2H, q, N-CH), δ 6.9-7.0 (2H, dd, trans-CH=CH), δ 7.1-
7.3 (5H, m, aromatic), δ 7.3-7.7 (4H, m, aromatic) ; MS: m/z
249.13 (M+).Anal. calcd. (%) for C17H16N2: C, 82.22; H, 6.49;
N, 11.28; Found C, 82.42; H, 6.56; N, 11.30.
RESULTS AND DISCUSSION
Reaction of o-phenylenediamine (1) with cinnamic acids
(2a-c) in glycerol at 180 °C resulted in 2-styrylbenzimidazoles
(3a-c) (i.e., 3a,Ar = C6H5), (3b, Ar = C6H4-p-Cl) and (3c,Ar =
C6H4-p-CH3) in good yields (Table-1) and the products were
identical with the ones reported in earlier methods25,26 in all
respects (m.p. m.m.p and co-TLC analysis). 2-Methylbenz-
imidazole (4), which was prepared by Philip's condensation27,
condensation of 1 with acetic acid using 4 N HCl, on reacting
with substituted benzaldehydes (5a-c) (i.e., 5a, Ar = C6H5),
1-Benzyl-2-styryl-1H-benzimidazole (7c) (Table-1,
entry 6):Yield (2.1 g, 70 %), m.p. 120-121 °C (Lit. m.p. 120
1
°C), IR (KBr, νmax, cm-1): 3020 (-CH=CH), 1624 (C=N), H
NMR (400 MHz, DMSO-d6): δ 4.9-5.0 (2H, s, N-CH), δ 6.9-
7.0 (2H, dd, trans-CH=CH), δ 7.0-7.4 (5H, m, aromatic), δ
7.1-7.3 (5H, m, aromatic), δ 7.3-7.8 (4H, m, aromatic), MS:
m/z 311.15 (M+). Anal. calcd. (%) for C22H18N2: C, 85.13; H,
5.85; N, 9.03; Found C, 85.16; H, 5.92; N, 9.79.

Vol. 25, No. 17 (2013)
Green Syntheses of N-Alkyl-2-styrylbenzimidazoles 9571
TABLE-1
SYNTHESIS OF COMPOUNDS 3a-c AND 7a-i FROM 1, 4 AND 6a-c RESPECTIVELY
S. No.
aProduct
R1
Time (h)
Temp. (°C)
100
bYield (%)
m.p. (°C)
205
1
2
3
3a(Ar = C6H5)
-
-
-
1
1
75
70
3b(Ar = C6H4-p-CH3)
3c(Ar = C6H4-p-Cl)
216-217
222
100
1
3
3
3
3
3
3
3
3
3
100
160
170
170
170
170
180
175
175
180
73
70
68
70
72
70
65
73
70
72
4
5
7a(Ar = C6H5)
CH3
114-115
158-160
120-121
129-130
108-110
210-212
143-145
171-172
>230
7b(Ar = C6H5)
C2H5
CH2Ph
CH3
6
7c (Ar = C6H5)
7
7d(Ar = C6H4-p-CH3)
7e(Ar = C6H4-p-CH3)
7f(Ar = C6H4-p-CH3)
7g(Ar = C6H4-p-Cl)
7h(Ar = C6H4-p-Cl)
7i(Ar = C6H4-p-Cl)
8
C2H5
CH2Ph
CH3
9
10
11
12
C2H5
CH2Ph
aAll the products were characterized by 1H NMR, IR and mass spectral data and comparison with the authentic samples available or prepared
according to reported methods.
bYields refers to isolated yields.
TABLE-2
N-ALKYL/ARALKYLATIONS OF COMPOUNDS
3a-c AND 4 USING SOLID PHASE SYNTHESIS
(BY SIMPLE PHYSICAL GRINDING)
(5b, Ar = C6H4-p-Cl) and (5c, Ar = C6H4-p-CH3) in glycerol at
170-180 °C for 1 h, resulted in 3a-c (i.e., 3a, Ar = C6H5), (3b,
Ar = C6H4-p-Cl) and (3c, Ar = C6H4-p-CH3) in good yields
(Table-1) also identical with the products obtained above in
all respects (m.p. m.m.p. and co-TLC analysis).
S.
No.
Solid-phase (simple
physical grinding)
Substrate
Reagent
Producta
Time Temp. Yieldb
The N-alkylation of (3a-c) and (4) and with alkylating
agents such as dimethyl sulphate (DMS), diethyl sulphate
(DES) and benzyl chloride (PhCH2Cl) in the presence of K2CO3
as a mild base and tetrabutylammonium bromide (TBAB) as
phase transfer catalyst, by a simple physical grinding of the
reactants in a mortar with a pestle under solvent-free conditions
for 5 min at room temperature, gave respectively, N-methyl-
2-styrylbenzimidazole (7a, i.e.,R1 = CH3,Ar = C6H5), N-ethyl-
2-styrylbenzimidazole (7b, i.e., R1 = C2H5,Ar = C6H5), N-ben-
zyl-2-styrylbenzimidazole (7c, i.e., R1 = PhCH2Cl,Ar = C6H5),
N-methyl-2-[(E)-2-(4-methylphenyl)ethenyl]-1H-1,3-benz-
imidazole (7d, i.e., R1 = CH3, Ar = C6H4-p-CH3), N-ethyl-2-
[(E)-2-(4-methylphenyl)ethenyl]-1H-1,3-benzimidazole (7e,
i.e., R1 = C2H5, Ar = C6H4-p-CH3), N-benzyl-2-[(E)-2-(4-
methylphenyl)ethenyl]-1H-1, 3-benzimidazole (7f, i.e., R1 =
PhCH2Cl, Ar = C6H4-p-CH3), N-methyl-2-[(E)-2-(4-
chlorophenyl)ethenyl]-1H-1,3- benzimidazole (7g, i.e., R1 =
CH3, Ar = C6H4-p-Cl), N-ethyl-2-[(E)-2-(4-chlorophenyl)
ethenyl]-1H-1, 3-benzimidazole (7h, i.e., R1 = C2H5,Ar = C6H4-
p-Cl) and N-benzyl-2-[(E)-2-(4-chlorophenyl)ethenyl]-1H-
1,3-benzimidazole (7i, i.e., R1 = PhCH2Cl, Ar = C6H4-p-Cl)
respectively (Table-2).
(min)
(%)
(°C)
RT
RT
RT
RT
RT
RT
RT
RT
RT
RT
RT
RT
1
2
3
4
DMS
5
5
80
78
90
80
75
78
90
80
78
80
78
80
3a
(R=CH3)
7a
7b
7c
7d
7e
7f
DES
Ph-CH2Cl
DMS
10
5
3b
(R=OH)
DES
8
Ph-CH2Cl
DMS
10
6
3c
(R=Cl)
7g
7h
7i
DES
10
10
5
Ph-CH2Cl
DMS
4
6a
6b
6c
DES
10
PhCH2Cl
10
aAll the products were characterized by 1H NMR, IR and mass spectral
data and comparison with the authentic samples available or prepared
according to reported methods.
bYields refers to the isolated yields
in PEG-600 at 100 °C about 1 h without the use of any base,
followed by simple processing, gave respectively, 7a-i and
6a-c (Table-3).
Compounds 7a-i) and 6a-c were also be prepared by an
alternative method. Thus, 3a-c and 4 on reactions, indepen-
dently, with each of dimethyl sulphate (DMS), diethyl sulphate
(DES) and benzyl chloride (PhCH2Cl) under microwave irra-
diation conditions for 5-10 min and subsequent processing,
gave 7a-i and 6a-c (Table-4).
Compound 4 on treatment with alkylating agents in the
presence of K2CO3 and TBAB under physical grinding condi-
tions in a mortar with pestle gave the products N-methyl-2-
methylbenzimidazole (6a, i.e., R = CH3), N-ehtyl-2-
methylbenzimidazole (6b, i.e., R = C2H5) and N-benzyl-2-
mehtylbenzimidazole (6c, i.e., R = PhCH2Cl) respectively and
these products were identical with the ones prepared earlier22,25
using conventional methods in all respects (m.p. m.m.p and
co-TLC analysis) (Table-2).
Conclusion
In conclusion, green and simple syntheses of 2-
styrylbenzimidazoles (3a-c) and their N-alkyl/aralkyl deriva-
tives 7a-i were described. It appears from this study that green
syntheses using solvents such as glycerol and PEG-600 and
eco-friendly methods like solid phase synthesis (physical grind-
ing) and microwave irradiation gives better yields, quality and
in less reaction time the products over conventional methods.
The entire sequence of reactions shown in Scheme-I has been
carried out using eco-friendly solvents and green conditions.
The N-alkylation reactions of 3a-c and 4 were also carried
out in PEG-600 as a solvent, both by heating at 100 °C on a
water bath and in microwave method. Thus the treatment of
3a-c and 4, independently, with each of dimethyl sulphate
(DMS), diethyl sulphate (DES) and benzyl chloride (PhCH2Cl)

9572 Kumar et al.
Asian J. Chem.
Scheme-I: Synthesis & N-alkylation studies of 2-styrylbenzimidazoles 7a-i
TABLE-3
ACKNOWLEDGEMENTS
N-ALKYL/ARALKYLATIONS OF COMPOUNDS
3a-c AND 4 USING PEG-600 AS SOLVENT (SOLUTION PHASE)
The authors are thankful to the authorities of Jawaharlal
Nehru Technological University Hyderabad, for providing
financial support and laboratory facilities.
S.No Substrate
Reagent
Producta Green solvent (solution
phase) in PEG-600
Time Temp Yieldb
(%)
(min)
60
(0C)
100
100
100
100
100
100
100
100
100
100
100
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82
75
72
80
70
75
83
76
78
75
68
3a
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7a
7b
7c
7d
7e
7f
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14. Y. Wang, K. Sarris, D.R. Sauer and S.W. Djuric, Tetrahedron Lett., 47,
4823 (2006).
TABLE-4
N-ALKYL/ARALKYLATIONS OF COMPOUNDS
3a-c AND 4 USING MICROWAVE
Producta
S.No Substrate Reagent
Microwave irradiation
Yieldb
(%)
Time
(min)
Temp
(0C)/
15. Y. Wang, H. Ma, X. Han and J. Wang, Heterocycles, 71, 1821 (2007).
16. Y. Tagawa, K. Yamagata and K. Sumoto, Heterocycles, 75, 415 (2008).
17. R. Varala, A. Nasreen, R. Enugala and S.R. Adapa, Tetrahedron Lett.,
48, 69 (2007).
Watt
DMS
3
5
5
5
5
5
5
5
5
5
5
100/450
100/450
100/450
100/450
100/450
100/450
100/450
100/450
100/450
100/450
100/450
88
80
75
80
78
75
88
78
75
85
82
7a
7b
7c
7d
7e
7f
18. P.K. John, L. Jesper and C.F.J. Raymond, Tetrahedron Lett., 41, 5410
(2000).
1.
2.
3a
(R=CH3)
DES
PhCH2Cl
DMS
19. V. Ravi, E. Ramu, K. Vijay and A.S. Rao, Chem. Pharm. Bull. (Tokyo),
55, 1254 (2007).
3b
(R=OH)
DES
20. A. Chawla, R. Kaur andA. Goyal, J. Chem. Pharm. Res., 3, 925 (2011).
21. P.K. Dubey, D.E. Rao, J. Ramanatham, R. Kumar and J.S. Grossert, J.
Indian Chem. Soc., 75, 460 (1998).
PhCH2Cl
DMS
3.
3c
(R=Cl)
7g
7h
7i
22. P.K. Dubey, R. Kumar, J.S. Grossert and D.L. Hooper, Indian J. Chem.,
37B, 288 (1998).
DES
PhCH2Cl
DES
23. P.K. Dubey and R. Kumar, Indian J. Chem., 38B, 1041 (1999).
24. K. Ramaiah, P.K. Dubey, D.E. Rao, J. Ramanatham and R. Kumar,
Indian J. Chem., 39B, 904 (2000).
6b
4.
4
PhCH2Cl
6c
aAll the products were characterized by 1H-NMR, IR and Mass spectral
data and comparison with the authentic samples available or prepared
according to reported methods.
25. P.K. Dubey and R. Kumar, Indian J. Heterocycl. Chem., 16, 131 (2006).
26. M.A. Phillips, J. Chem. Soc., 928, 2393 (1928).
27. K. Selvam and M. Swaminathan, Tetrahedron Lett., 52, 3386 (2011).
bYields refers to the isolated yields