Microwave-assisted synthesis of chalcones, flavanones and 2-pyrazolines: Theoretical and experimental study

Article abstract of DOI:10.2174/157017812802139609

Condensation of 2-acetyl-1-naphthol and 1-acetyl-2-naphthol with benzaldehydes under microwave irradiation gave chalcones or flavanones depending on the type of ketone. Also, 2-pyrazolines were synthesized by the condensation of chalcones with phenyl hydrazine under microwave irradiation in presence of dry acetic acid as a cyclizing agent. The results obtained indicated that, unlike classical heating, microwave irradiation resulted in higher yields, shorter reaction times and cleaner reactions. The structures of the synthesized compounds were elucidated using various spectroscopic methods. Theoretical studies explained the behaviour and reactivity observed for 1-acetyl-2-naphthol with benzaldehydes considering geometries, and electron densities of the formed flavanones.

Full text of DOI:10.2174/157017812802139609

530
Letters in Organic Chemistry, 2012, 9, 530-537
Microwave–assisted Synthesis of Chalcones, Flavanones and 2-
pyrazolines: Theoretical and Experimental Study
Abdullah S. Al-Bogami*
Department of Chemistry, Faculty of Science, King Abdulaziz University, North Jeddah, P.O. Box 80203 Jeddah 21589,
Saudi Arabia
Received April 02, 2012: Revised May 28, 2012: Accepted June 20, 2012
Abstract: Condensation of 2-acetyl-1-naphthol and 1-acetyl-2-naphthol with benzaldehydes under microwave irradiation
gave chalcones or flavanones depending on the type of ketone. Also, 2-pyrazolines were synthesized by the condensation
of chalcones with phenyl hydrazine under microwave irradiation in presence of dry acetic acid as a cyclizing agent. The
results obtained indicated that, unlike classical heating, microwave irradiation resulted in higher yields, shorter reaction
times and cleaner reactions. The structures of the synthesized compounds were elucidated using various spectroscopic
methods. Theoretical studies explained the behaviour and reactivity observed for 1-acetyl-2-naphthol with benzaldehydes
considering geometries, and electron densities of the formed flavanones.
Keywords: 1-Acetyl-2-naphthol, 2-Acetyl-1-naphthol, 2-Pyrazolines, chalcones, flavanones, microwave irradiation.
INTRODUCTION
celerated reaction of ꢀ,ꢁ-unsaturated aldehydes and ketones
with hydrazines for the rapid assembly of 2-pyrazolines [32-
34].
Chalcones, either natural or synthetic, are known to ex-
hibit various biological activities [1] such as antioxidant [2],
anti-inflammatory [3], antimalarial [4], and antitumor [5].
Also, they are of high interest due to their usage as starting
materials in synthesis of a series of heterocyclic compounds
[6-9]. 2-hydroxychalcones are considered as precursors in
the synthesis and biosynthesis of several flavonoids, such as
flavanones, flavones, isoflavones and aurones [10-15]. The
members of the flavanoid [16] family are attracting in-
creased attention due to their anticancer [17], antinflamma-
tory [18], antimalarial [19] and anti-AIDS [20] pharmacol-
ogical activities. These findings explain the significant inter-
est of chemists, biochemists and pharmacologists in this par-
ticular group of compounds.
RESULTS AND DISCUSSION
A series of chalcones 3 was prepared from the reaction of
2-acetyl-1-naphthol 1 with benzaldehydes 2 under micro-
wave irradiation (Scheme 1, Table 1).
The formation of the chalcones 3a-d was confirmed on
the basis of their IR and 1H-NMR data. They show a charac-
teristic IR absorption peak at 1700-1650 cm-1 indicating the
presence of a conjugated carbonyl group (>C=O). The main
features of NMR data of chalcones 3a-d are the resonances
of: (i) the hydroxyl groups at about ꢂ = 14.5 ppm. The high
frequency resonances of these protons are due to the in-
tramolecular hydrogen bond formed with the carbonyl
Pyrazolines are well known and important nitrogen-
containing five-membered heterocyclic compounds and
various methods have been worked out for their synthesis.
[21-24]. Several pyrazoline derivatives have been found to
possess considerable biological activities, which stimulated
research activity in this field. Their prominent effects are
such as antimicrobial [25], central nervous system [26], and
immunosuppressive [27] activities. 2-Pyrazolines seem to be
the most frequently studied pyrazoline type compounds. Af-
ter the pioneering work of Fischer and Knövenagel in the
late nineteenth century [28], and in a continuation of our
research, in the synthesis of a wide range of heterocyclic
compoubds, for biological screening programme in our labo-
ratory [29-31], the current work describes a microwave ac
group; (ii) the vinylic protons appearing as doublets at ꢂH-
ꢀ
7-8 ppm and ꢂH- 7.5-8 ppm. (iii) the vinylic carbons which
ꢁ
appear at ꢀC- 123-132 ppm and ꢂC-ꢁ 137-144 ppm. The CHN
ꢀ
analysis and MS spectra of these compounds are in agree-
ment with the proposed structures (Table 2).
The chalcones 3a-d were then reacted with phenyl hy-
drazine to give 2-pyrazoline compounds 4a-d. This reaction
probably takes place through mediation of an appropriate ꢀ,
ꢁ-unsaturated hydrazone, which immediately cyclizes to
give a 2-pyrazoline ring in the presence of a suitable cycliz-
ing agent like dry acetic acid under microwave irradiation
(Scheme 2, Table 3). The products formed 4a-d was often
accompanied by small traces (1%) of the hydrzaid derivative
(Scheme 2). These latest was easily eliminated by washing
the crystallized major product with diethyl ether.
*Address correspondence to this author at the Department of Chemistry,
Faculty of Science, King Abdulaziz University, North Jeddah, P.O BOX
80203 Jeddah 21589, Saudi Arabia; Tel: +966554433416; Fax: +966
26400376; E-mail: chem_org@hotmail.com
Structures of all new 2-pyrazolines have been elucidated
by microanalyses, IR and NMR spectroscopic measure-
1875-6255/12 $58.00+.00
© 2012 Bentham Science Publishers

Microwave–assisted Synthesis of Chalcones, Flavanones and 2-pyrazolines
Letters in Organic Chemistry, 2012, Vol. 9, No. 7 531
OH
O
O
H
ꢀ
ꢁ
OH
O
R1
R4
R1
R2
MW (100 watt)
KOH-MeOH
1-2 min.
R2
R3
CH3
+
R4
R3
1
2
3
Scheme 1. Microwave assisted synthesis of chalcone 3a-d.
Table 1. Chalcones 3 Derivatives
R1
R2
R3
R4
Product
Yield (%)
H
H
H
H
H
Cl
H
H
3a
3b
3c
3d
94
90
91
87
H
OMe
H
OMe
Cl
OMe
H
Cl
Table 2. 1H and 13C Chemical Shifts (ꢀ, Ppm, in CDCl3) of Compounds (3a-d)
Compound
H-ꢁ
H-ꢂ
OH
C-OH
C=O
3a
3b
3c
3d
7.67
7.94
7.80
7.79
7.86
8.53
7.88
8.28
14.86
14.71
14.91
14.70
164.51
164.62
164.46
164.73
193.31
193.02
193.04
192.70
OH
O
R4
R2
NHNH2
ꢀ
ꢁ
OH HN
N
R1
R3
MW (300 watt)
AcOH, 4-10 min.
R2
R3
+
HX
R1
HA HB
4
+
R4
CH3CONHNHPh
(1%)
3
Scheme 2. Microwave assisted synthesis of 2-pyrazolines 4a-d.
Table 3. 2-pyrazolines 4 Derivatives
R1
R2
R3
R4
Product
Yield (%)
H
H
H
H
H
Cl
H
H
4a
4b
4c
4d
83
91
80
85
H
OMe
H
OMe
Cl
OMe
H
Cl
ments. Elemental analyses unambiguously proved the ele-
mental composition of all new compounds. The IR spectra of
compounds 4a-d gave characteristic band at 3650-3500 cm-1
(OH), 1590-1580 (C=N). In the 1H NMR spectra of 2-
pyrazolines 4a-d the three hydrogen atoms attached to the C-
4 and C-5 carbon atoms of the heterocyclic ring gave an
ABX spin system. Measured chemical shift and coupling
constant values unequivocally prove the 2-pyrazoline struc-
ture (Table 4).

532 Letters in Organic Chemistry, 2012, Vol. 9, No. 7
Abdullah S. Al-Bogami
Table 4. 1H NMR Spectral Data of 4a-d in CDCl3.
Compound
4a
HA
HB
HX
3.36(dd)
(J=16.84,7.36Hz)
4.05(dd)
(J=16.84,11.72Hz)
5.26(dd)
(J=12.48,8.8Hz)
3.25(dd)
(J=16.84,7.36Hz)
3.92(dd)
(J=16.84,12.48Hz)
5.10(dd)
(J=12.44,8.08Hz)
4b
4c
4d
3.34(dd)
(J=16.85,7.36Hz)
4.03(dd)
(J=16.88,11.72Hz)
5.13(dd)
(J=11.72,8.04Hz)
3.26(dd)
(J=16.84,7.36Hz)
4.17(dd)
(J=16.88,11.72Hz)
5.58(dd)
(J=11.72,8.04Hz)
Table 5. 13C NMR Spectral Data of 4a-d in CDCl3
Compound
C-4
C-5
C-OH
4a
4b
4c
4d
44.42
44.25
44.60
42.69
63.55
62.82
60.69
59.94
154.29
154.28
154.03
154.03
R2
D
R1
Hax
R3
R4
O
C
O
one
step
A
B
H
H3C
O
O
Flavanone 6
R2
R1
R2
OH
MW(100 Watt)
+
KOH/MeOH
1-2 min.
R1
R3
R4
R4
5
O
R3
OH
6,7 R1
R2
R3 R4
a
b
c
d
H
H
H
H
H
H
H
Cl
H
H
Chalcone 7
(not obtaind)
OMe OMe OMe
Cl Cl
H
Scheme 3. Microwave assisted synthesis of flavanones 6a-d.
Table 6. Flavanones 6 Derivatives
R1
R2
R3
R4
Product
Yield (%)
H
H
H
H
H
Cl
H
H
6a
6b
6c
6d
94
90
89
92
H
OMe
H
OMe
Cl
OMe
H
Cl
13C NMR chemical shift values of carbon atoms C-3
(146-150 ppm), C-4 (43-44 ppm) and C-5 (62-64 ppm) cor-
roborate the 2-pyrazoline structure deduced from the H-
undergoes intramolecular cyclization in the second step to
yield flavanone. In this work, we found out that flavanones
can be synthesized in good yields from 1-acetyl-2-naphthol
(5) and benzaldehydes (2) using KOH as catalyst in one step
without formation of chalcone 7 (Scheme 3, Table 6).
1
NMR spectroscopic data (Table 5).
The main method for the synthesis of flavanones involves
two steps. The first step is Claisen–Schmidt condensation of
aromatic aldehydes and ketones yielding chalcone. Chalcone
Compounds 6a-d (Table 6) show in the IR spectra absor-
bances for the carbonyl group at about 1690 cm-1. The 1H

Microwave–assisted Synthesis of Chalcones, Flavanones and 2-pyrazolines
Letters in Organic Chemistry, 2012, Vol. 9, No. 7 533
Table 7. 1H and 13C Chemical Shifts (ꢀ, Ppm, in CDCl3) of Compounds (6a-d)
Compound
H-2
Hax
Heq
C-2
C-3
C=O
6a
6b
6c
6d
5.35
5.58
5.48
5.92
2.98
3.20
3.23
3.09
2.90
2.97
2.93
2.94
163.70
167.28
164.42
163.70
163.53
163.53
163.64
163.53
192.74
192.65
193.02
193.85
Dipole moment of 6a (Debye)= 2.5491
Dipole moment of 6b (Debye)= 2.6585
Dipole moment of 6d (Debye)= 3.8272
Dipole moment of 7a (Debye)= 5.8479
Dipole moment of 7b (Debye)= 6.6341
Dipole moment of 7d (Debye) = 6.4144
Fig. (1). Geometrical parameters, charge distribution and dipole moment for proposed structures (6a, 6b, 6d, 7a, 7b and 7d) using HF calcu-
lations.
NMR spectrum showed a flavanone structure with the sig-
nals at about ꢀ = 5.57 (1H, dd, J = 13.92, 2.92 HZ, H-2) and
3.16 (1H, dd, J = 16.88, 2.96 HZ, Hax), 2.9 (1H, dd, J =
16.12, 2.92 HZ, Heq), which are typical for the C ring. The
13C NMR and MS spectra of these compounds are in
agreement with the proposed structures (Table 7).
explore the different pathways of the chemical reaction in
Scheme 3. The structure optimizations were performed with
the HF/6-31G* using the GAUSSIAN 03 program system
[35]. Vibrational frequency analyses were carried out for the
optimized structures in order to assess the nature of station-
ary points. The characteristic of local minima was verified
by have no imaginary frequency. The relative energies, di-
pole moments, charge distribution and the structural parame-
ters are given in Fig. (1).
To further understand our current experimental results in
scheme 3, we carried out Hartree-Fock (HF) calculations to

534 Letters in Organic Chemistry, 2012, Vol. 9, No. 7
Abdullah S. Al-Bogami
Fig. (2). Frontier Molecular orbitals for the studied structures using HF/6-31G* level.
According to the results given in Fig. (1), the structure of
product 7 (not formed product) is more stable than proposed
structure 6 (already formed product). But the extra stability
of product 6 which pushes reaction to form it is mainly due
to the formation of the ring and assisted by electron delocali-
zation (Fig. 2).
1106 EA instrument their results were found to be in good
agreement (±0.3%) with the calculated values”. For the mi-
crowave irradiation we used a 800 W STAR SYSTEM-2
monomode reactor (CEM Corporation). TLC was performed
on (TLC plates silica gel 60F245 pre-coated 20ꢁ20 cm layer
thickness 0.25 mm).
General procedure for the preparation of chalcones
(3a-d) In a typical procedure, a mixture of 2-acetyl-1-
naphthol (2.69 mmol) and benzaldehydes (2.69 mmol) in 2
eq KOH/MeOH was charged in a MW test tube (10 mL)
containing a magnetic stirring bar and a rubber cap and 2mL
of methanol. The test tube was placed in the microwave cav-
ity (CEM, Discover). The tube was subjected to MW a 70°C
(power 100 W) for 1-2 min. After completion of the reac-
tion, the tube was removed, cooled to room temperature, and
the reaction mixture was poured into crushed ice water (30
ml). Then conc. HCl (1 ml) was added and the reaction mix-
ture was left to stay at 2-3oC overnight. The separated solid
was collected by filtration and recrystallized from methanol.
CONCLUSION
A very useful and rapid method via microwave assisted
synthesis of chalcone, 2-pyrazoline and flavanones is de-
scribed. Furthermore, the combined use of experimental de-
sign with theoretical calculations, including evaluation of
behavior and reactivity of 1-acetyl-2-naphthol with benzal-
dehydes to form flavanones provides with a powerful tool to
design the synthesis of more derivatives using different sub-
stituents, which could help to produce environmentally
friendly bioactive compounds.
The difference in behavior between compound 1 and
compound 5 in our opinion may be due to 2-OH in com-
pound 5 considered a better nucleophile than 1-OH in com-
pound 1.
1-(1-Hydroxy-naphthalen-2-yl)-3-phenyl-propenone (3a)
This compound was prepared from 2-acetyl-1-naphthol
and benzaldehyde. Yield = 94 %, green needles, mp 123-
EXPERIMENTAL
1
125oC; IR: 1590 (C=C), 1700 (C=O), 3100 (OH); H NMR
Melting points were determined on Gallenkamp-melting
point apparatus. IR spectra were recorded on a Perkin-Elmer
883 spectrophotometer as KBr pellets and expressed as ꢀ in
cm-1. NMR spectra were recorded on JEOL ECP 400 (400
MHz) in CDCl3 and expressed as ꢀ in ppm. Mass spectra
were recorded on Shimadzu QP-5050A GC/MS system.
Elemental analyses (C, H, N) were performed on Carlo Erba
(400 MHz, CDCl3): ꢀ 7.27-8.04 (11H, m), 7.67 (1H-ꢂ, d, Jꢀ
ꢃ
,
= 15.4 Hz), 7.86 (1H-ꢁ, d, Jꢀ ꢁ = 15.4 Hz), 14.86 (1H, s). 13
C
,
NMR: ꢂ 113.55, 118.32, 120.53, 123.99, 124.60, 125.57,
126.03, 127.49, 128.77, 129.13, 130.30, 130.39, 134.84,
137.47, 145.16, 164.51, 193.31, MS: m/z (%) 274 (M+, 19),
197, 170, 103, 89, 77, 65, 51; Anal. calcd. (%) for C19H14O2:
C, 83.19; H, 5.14. Found (%): C, 83.10; H, 5.20.

Microwave–assisted Synthesis of Chalcones, Flavanones and 2-pyrazolines
Letters in Organic Chemistry, 2012, Vol. 9, No. 7 535
3-(4-Chloro-phenyl)-1-(1-hydroxy-naphthalen-2-yl)-
propenone (3b)
5.26 (1H, dd, J = 12.48, 8.8HZ, HX), 6.84-8.47 (16H, m),
11.74 (1H, s).;13C NMR: 44.42, 63.55, 109.50, 113.41,
119.07, 119.90, 123.20, 123.75, 125.71, 126.02, 126.06,
127.45, 127.48, 127.93, 129.21, 129.37, 134.52, 142.08,
144.26, 150.37, 154.29; MS: m/z (%) 364 (M+, 65), 170,
103,91, 89, 77, 65,51 ; Anal. calcd. (%) for C25H20N2O C,
82.39; H, 5.53; N, 7.69. Found (%): C, 82.22; H, 5.12; N,
7.16.
This compound was prepared from 2-acetyl-1-naphthol
and 4-chlorobenzaldehyde. Yield = 90 %, red needles, mp
170-173oC; IR: 1602 (C=C), 1670 (C=O), 3150 (OH); H
1
NMR (400 MHz, CDCl3): ꢀ 7.21-7.85 (10H, m), 7.94 (1H-ꢁ,
d, Jꢀ,ꢁ = 15.4 Hz), 8.53 (1H- ꢁ, d, Jꢀ ꢁ = 15.4 Hz), 14.71(1H,
,
s). 13C NMR: ꢂ 113.48, 118.41, 121.02, 123.88, 124.63,
125.56, 126.11, 127.52, 129.43, 129.89, 130.42, 133.35,
136.85, 137.52, 143.62, 164.62, 193.02, MS: m/z (%) 310
(M+2, 22), 308 (M+, 55), 170, 103, 89, 77, 65, 51. ; Anal.
calcd. (%) for C19H13ClO2: C, 73.91; H, 42.44. Found (%):
C, 73.20; H, 42.09.
2-[5-(4-Chloro-phenyl)-1-phenyl-4,5-dihydro-1H-pyrazol-
3-yl]-naphthalen-1-ol (4b)
This compound was prepared from 3b and phenyl hydra-
zine Yield = 91 %, green powder , mp 175-176oC; IR: 1685
1
(C=N); H NMR (400 MHz, CDCl3): 3.25 (1H, dd, J =
1-(1-Hydroxy-naphthalen-2-yl)-3-(3,4,5-trimethoxy-
phenyl)-propenone (3c)
16.84, 7.36 HZ, HA), 3.92 (1H, dd, J = 16.88, 12.48 HZ, HB),
5.10 (1H, dd, J = 12.44, 8.08 HZ, HX),6.83-8.47 (15H, m),
11.71 (1H, s).; 13C NMR: 44.25, 62.82, 109.34, 113.44,
119.18, 120.14, 123.21, 123.72, 125.79, 127.47, 127.56,
129.30, 129.57, 133.70, 134.56, 140.57, 144.04, 150.39,
154.28; MS: m/z (%) 400 (M+2, 36),398 (M+, 100) 170,
103,91, 89, 77, 65,51 ; Anal. calcd. (%) for C25H19ClN2O C,
75.28; H, 4.80; N,7.02. Found (%): C, 75.43; H, 4.92;
N,7.10.
This compound was prepared from 2-acetyl-1-naphthol
and 3,4,5-trimethoxybenzaldehyde. Yield = 91 %, red pow-
der , mp 115-116oC; IR: 1609 (C=C), 1668 (C=O), 3100
1
(OH); H NMR (400 MHz, CDCl3): 3.92 (3H, s), 3.93 (6H,
s), 6.87(2H,s), 7.27 (1H ,d , J =8.8HZ) 7.51-7.61 (3H, m),
7.80 (1H- ꢁ, d, Jꢀ ꢁ = 15.4 Hz), 7.88 (1H- ꢁ, d, Jꢀ ꢁ = 15.4
,
,
Hz), 8.48 (1H,d,J=8.08HZ), 14.91 (1H, s).13C NMR: 56.32,
61.14, 105.95, 113.50, 118.25, 119.56, 123.80, 124.54,
125.54, 126.01, 127.48, 130.28, 137.41, 140.74, 145.32,
153.56, 164.46, 193.04; MS: m/z (%)364 (M+, 100), 194,
179,115, 103, 89, 77, 65, 51. ; Anal. calcd. (%) for C22H20O5:
C, 72.51; H, 5.53. Found (%): C, 72.29; H, 5.77.
2-[1-Phenyl-5-(3,4,5-trimethoxy-phenyl)-4,5-dihydro-1H-
pyrazol-3-yl]-naphthalen-1-ol (4c)
This compound was prepared from 3c and phenyl hydra-
zine
Yield = 77 %, green powder , mp 166-168oC; IR: 1692
(C=N); H NMR (400 MHz, CDCl3): 3.34 (1H, dd, J =
3-(2,4-Dichloro-phenyl)-1-(1-hydroxy-naphthalen-2-yl)-
propenone (3d)
1
16.85, 7.36 HZ, HA), 3.82 (3H, s), 3.88 (6H, s) 4.03 (1H, dd,
J = 16.88, 11.72 HZ, HB), 5.13 (1H, dd, J = 11.72, 8.04HZ,
HX), 6.58-8.45 (13H, m), 11.80 (1H, s).; 13C NMR: 44.60,
56.27, 60.69, 64.52, 102.48, 109.41, 113.58, 119.14, 120.20,
123.17, 123.77, 124.79, 125.79, 127.53, 129.24, 134.66,
137.33, 137.70, 144.72, 150.72, 154.03; MS: m/z (%) 454
(M+, 100) 170, 103,91, 89, 77, 65,51 ; Anal. calcd. (%) for
C28H26N2O4 C, 73.99; H, 5.77; N,6.16. Found (%): C, 73.15;
H, 5.65; N,6.11.
This compound was prepared from 2-acetyl-1-naphthol
and 2,4-dichlorobenzaldehyde Yield = 87 %, red powder, mp
1
167-169oC; IR: 1619 (C=C), 1655 (C=O), 3111 (OH); H
NMR (400 MHz, CDCl3): 6.87 (2H,s),7.27 (1H ,d , J =
8.8HZ) ,7.27-7.76 (7H, m), 7.79 (1H- ꢁ, d, Jꢀ ꢁ = 15.4 Hz),
,
8.28 (1H-ꢁ, d, Jꢀ ꢁ = 15.4 Hz), 8.50 (1H, d, J = 8.08HZ),
,
14.70 (1H,s).;13C NMR: 113.40, 118.49, 123.43, 123.80,
124.66, 125.50, 126.14, 127.51, 127.68, 128.62, 130.32,
130.52, 131.75, 136.36, 137.40, 139.50, 164.73, 192.70; MS:
m/z (%) 344 (M+2, 14), 342 (M+, 20), 307, 197, 170, 103,
89, 77, 65, 51. ; Anal. calcd. (%) for C19H12Cl2O2: C, 66.49;
H, 3.52. Found (%): C, 66.80; H, 3.66.
2-[5-(2,4-Dichloro-phenyl)-1-phenyl-4,5-dihydro-1H-
pyrazol-3-yl]-naphthalen-1-ol (4d)
This compound was prepared from 3d and phenyl hydra-
General Procedure for the Preparation of 2-pyrazolines
(4a-d)
zine Yield = 85 %, yellow powder, mp 188-189oC; IR: 1695
1
(C=N); H NMR (400 MHz, CDCl3): 3.26 (1H, dd, J =
In a typical procedure, the phenylhydrazine reagent (3
mmol) is then added dropwise to a stirring solution of the
chalcones 3a-d (1 mmol) in glacial AcOH (5 ml). The mix-
tures subjected to microwave heating for several min. using
a (CEM, Discover) microwave oven (300 watt) to afford 2-
pyrazolines, which washed with ether and recrystallized
from absolute ethanol then washed with ether to give pure
compounds 4a-d with a 77-91% yield.
16.84,7.36 HZ, HA), 4.17 (1H, dd, J = 16.88, 11.72 HZ, HB),
5.58 (1H, dd, J = 11.72, 8.04 HZ, HX),6.90-8.47 (14H,
m),11.69 (1H, s).;13C NMR: 42.69, 59.94, 109.48, 113.16,
119.22, 120.27, 123.24, 123.72, 125.82, 127.54, 127.65,
128.20, 128.49, 129.45, 129.98, 132.60, 143.72, 150.84,
154.03; MS: m/z (%) 454 (M+, 100) 170, 103,91, 89, 77,
65,51 ; Anal. calcd. (%) for C25H18Cl2N2O C, 69.29; H, 4.19;
N, 6.46. Found (%): C, 69.44; H, 4.15; N,6.33.
2-(1,5-Diphenyl-4,5-dihydro-1H-pyrazol-3-yl)-naphthalen-
1-ol (4a)
General Procedure for the Preparation of Flavanones (6a-
d)
This compound was prepared from 3a and phenyl hydra-
These compounds were prepared from 1-acetyl-2-
naphthol and benzaldehydes using conditions similar to
those described in general procedure for synthesis of chal-
cones 3.
zine Yield = 83 %, green powder, mp 179-180oC; IR: 1687
1
(C=N); H NMR (400 MHz, CDCl3): 3.36 (1H, dd, J =
16.84, 7.36 HZ, HA), 4.05 (1H, dd, J = 16.84, 11.72 HZ, HB),

536 Letters in Organic Chemistry, 2012, Vol. 9, No. 7
Abdullah S. Al-Bogami
3-Phenyl-2,3-dihydro-benzo[f]chromen-1-one (6a)
ACKNOWLEDGEMENTS
This compound was prepared from 1-acetyl-2-naphthol 5
and benzaldehyde. Yield = 95 %, brown powder, mp 106-
The author is highly thankful to Dr. Hamad Z. Alkhath-
lan, Professor of Chemistry Department, King Saud Univer-
sity for valuable suggestions and guidance.
o
1
108 C; IR: 1698 (C=O); H NMR (400 MHz, CDCl3): 5.35
(1H, dd, J = 13.92, 2.92 HZ,H-2) and 2.89 (1H, dd, J =
16.88, 2.92 HZ, Hax), 2.98 (1H, dd, J = 16.12, 2.92 HZ, Heq);
13C NMR: 45.50, 77.35, 112.33, 118.83, 124.82, 125.64,
126.14, 128.40, 128.74, 129.11, 129.53, 131.27, 137.51,
138.37, 163.53, 192.74; MS: m/z (%) 274 (M+, 100),
197,161,134, 105, 77, 65,51 ; Anal. calcd. (%) for C19H14O2
C, 83.19; H, 5.14. Found (%): C, 83.28; H, 5.01.
CONFLICT OF INTEREST
The author(s) confirm that this article content has no con-
flicts of interest.
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1
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, mp 99-101 C; IR: 1710 (C=O); H NMR (400 MHz,
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