NMR spectral and structural studies on some xanthenones and their thiosemicarbazone derivatives: Crystal and molecular structure of 12-(2-chlorophenyl)-8,9,10,12-tetrahydrobenzo[a]xanthen-11-one

Article abstract of DOI:10.1016/j.molstruc.2011.11.003

A series of 12-aryl-8,9,10,12-tetrahydrobenzo[a]xanthen-11-ones [1a-9a] were prepared employing a three component one-pot reaction of aryl aldehyde, 2-naphthol and 1,3-cyclohexanedione using BF₃·OEt₂ as catalyst. Thiosemicarbazone de

Full text of DOI:10.1016/j.molstruc.2011.11.003

Journal of Molecular Structure 1008 (2012) 8–16
Contents lists available at SciVerse ScienceDirect
Journal of Molecular Structure
journal homepage: www.elsevier.com/locate/molstruc
NMR spectral and structural studies on some xanthenones and their
thiosemicarbazone derivatives: Crystal and molecular structure
of 12-(2-chlorophenyl)-8,9,10,12-tetrahydrobenzo[a]xanthen-11-one
⇑
A. Sethukumar, V. Vithya, C. Udhaya Kumar, B. Arul Prakasam
Department of Chemistry, Annamalai University, Annamalainagar, 608 002 Chidambaram, India
a r t i c l e i n f o
a b s t r a c t
Article history:
A series of 12-aryl-8,9,10,12-tetrahydrobenzo[a]xanthen-11-ones [1a–9a] were prepared employing a
three component one-pot reaction of aryl aldehyde, 2-naphthol and 1,3-cyclohexanedione using BF3ꢀOEt2
as catalyst. Thiosemicarbazone derivatives [1b–5b] were also prepared in the presence of acid catalyst.
All the synthesized compounds have been characterized by IR and NMR. The structure of 5b was con-
firmed by HSQC spectral analysis. Single crystal X-ray structural analysis of 12-(2-chlorophenyl)-
8,9,10,12-tetrahydrobenzo[a]xanthen-11-one evidences the envelope and flattened-boat conformations
of cyclohexenone and pyran rings respectively.
Received 15 September 2011
Received in revised form 4 November 2011
Accepted 5 November 2011
Available online 16 November 2011
Keywords:
Xanthenone
Thiosemicarbazone
NMR
Ó 2011 Elsevier B.V. All rights reserved.
XRD
1. Introduction
tericide activity and in laser technologies [11–15]. Because of their
wide range of pharmacological, industrial and synthetic applica-
Multi Component Reactions (MCRs) have been emerged as an
extremely powerful tool in combinatorial chemistry and drug dis-
covery, since it offers significant advantages over conventional lin-
ear step syntheses [1]. The challenge is to conduct an MCR in such a
way that the network of pre-equilibrated reactions channel into
the main product and do not yield side products. The result is
clearly dependent on the reaction conditions: solvent, tempera-
ture, catalyst, concentration of the starting materials and func-
tional groups.
Xanthones are secondary metabolites found in higher plant
families, fungi and lichens [2]. This class of compounds exhibits
interesting pharmaceutical properties; specifically, antibacterial,
anti-inflammatory, anticancer and antiviral activities have been
observed [3–6]. Xanthenes and benzoxanthenes constitute an
important class of biologically active heterocycles and their syn-
thesis has been received great attention in the field of medicinal
and pharmaceutical chemistry owing to their broad spectrum of
pharmacological activities such as antibacterial [7], anti-inflamma-
tory [8] and antiviral [9]. Some of the xanthene based compounds
have found applications as antagonists for paralyzing the action of
zoxalamine and in photodynamic therapy [10]. In addition, their
derivatives can be used as dyes, pH sensitive fluorescent materials
for the visualization of biomolecular assemblies, agricultural bac-
tions 12-aryl-8,9,10,12-tetrahydrobenzo[a]xanthen-11-ones are
in lime light and recently many synthetic procedures are reported
in the literature [16–29]. Most of the reported procedures for the
synthesis of xanthenes derivatives accompanying with one or
other kinds of the disadvantages, such as, expensive reagents, pro-
longed reaction time, tedious work-up procedures, high catalyst
loading and strongly acidic conditions. Therefore, to avoid these
limitations, a readily available catalyst with high catalytic activity,
short reaction time and simple work-up for the preparation of
xanthenes is highly desirable.
In this paper we report the synthesis of a series of 12-aryl-
8,9,10,12-tetrahydrobenzo[a]xanthen-11-ones and their thiosemi-
carbazone derivatives. The derived compounds were characterized
by IR, NMR. The single crystal X-ray structural analysis of 12-(2-
chlorophenyl)-8,9,10,12-tetrahydrobenzo[a]xanthen-11-one (2a)
is also reported.
2. Experimental
Chemicals obtained from commercially available analytical
grade materials were used as supplied, without further purifica-
tion. IR spectra were recorded on Avatar Nicholet FT-IR spectro-
photometer (range 4000–400 cmꢁ1
)
as KBr pellets. 1H NMR
spectra were recorded on Bruker AMX-400 spectrometer operating
at 400.23 MHz and Bruker AVIII 500 MHz spectrometer operating
at 500.13 MHz using TMS as internal reference. 13C NMR spectra
⇑
Corresponding author. Tel.: +91 9443583619.
E-mail address: arul7777@yahoo.com (B. Arul Prakasam).
0022-2860/$ - see front matter Ó 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.molstruc.2011.11.003

A. Sethukumar et al. / Journal of Molecular Structure 1008 (2012) 8–16
9
were recorded on Bruker AMX-400 spectrometer operating at
100.63 MHz and Bruker AVIII 500 MHz spectrometer operating at
125.75 MHz.
allowed to dry and the obtained solids were recrystallized using
ethanol as solvent.
2.1.1. 12-Phenyl-8,9,10,12-tetrahydrobenzo[a]xanthen-11-one 1a
White crystals, yield: 75%. m.p. 188–191 °C; IR (KBr, cmꢁ1):
3056, 2957, 2927, 1647, 1592, 1373, 1187. 1H NMR (CDCl3,
500 MHz, ppm) d: 8.01–7.08 (m, 11H), 5.78 (s, 1H), 2.69–2.79 (m,
2H), 2.37–2.51 (m, 2H), 1.99–2.09 (m,2H). 13C NMR (CDCl3,
125 MHz, ppm) d: 197.0, 165.5, 147.8, 145.0, 131.5, 131.4, 128.8,
128.5, 128.3, 128.2, 127.0, 126.2, 124.9, 123.7, 117.7, 116.9,
115.6, 37.0, 34.6, 27.7, 20.3.
2.1. General procedure for the preparation of compounds 1a–9a
Compounds 1a–9a, were prepared by the general procedure
(Scheme 1) in which aldehyde (1.0 mmol), 2-naphthol (1.0 mmol)
and 1,3-cyclohexanedione (1.0 mmol) were mixed thoroughly
and placed in a 150 mL round-bottomed flask. The mixture was
dissolved in 75 mL of distilled ethanol and BF3:OEt2 (0.04 mmol)
was added to it. It was refluxed and the reaction was monitored
by thin layer chromatography. After the completion of reaction
(3 h), the reaction mixture was poured into cold water and the so-
lid separated was filtered, washed with water and a small amount
of ice cold ethanol. Then the obtained solid was purified by column
chromatography (on neutral alumina gel and by using benzene and
ethyl acetate (9.8:0.2) as eluent). The separated fractions were
2.1.2. 12-(2-Chlorophenyl)-8,9,10,12-tetrahydrobenzo[a]xanthen-11-
one 2a
White crystals, yield: 80%. m.p. 228–230 °C; IR (KBr, cmꢁ1):
3057, 2958, 2924, 2849, 1653, 1593, 1371,1227, 1190, 746. 1H
NMR (CDCl3, 500 MHz, ppm) d: 8.24–7.01 (m, 10H), 6.04 (s, 1H),
2.73–2.84 (m, 2H), 2.41–2.45 (m, 2H), 2.01–2.12 (m, 2H). 13C
Scheme 1.

10
A. Sethukumar et al. / Journal of Molecular Structure 1008 (2012) 8–16
Table 2
Table 1
Selected bond distances (Å) and angles for 2a.
Crystal data and structure refinement details for 2a.
Bond length
C(1)AC(6)
C(1)AO(1)
C(1)AC(2)
C(2)AC(30)
C(2)AC(3)
C(3)AC(4)
C(30)AC(4)
C(4)AC(5)
C(5)AO(2)
C(5)AC(6)
C(6)AC(7)
C(7)AC(8)
C(7)AC(18)
C(8)AC(17)
C(17)AO(1)
C(23)ACl(1)
Empirical formula
Formula weight
Temperature
C23H17ClO2
360.82
293(2) K
0.71073 Å
Monoclinic, P21/n
1.334(2)
1.360(2)
1.493(2)
1.492(8)
1.5465(8)
1.431(3)
1.447(8)
1.502(3)
1.209(2)
1.469(2)
1.515(2)
1.520(2)
1.529(2)
1.365(2)
1.384(2)
1.733(2)
Wavelength
Crystal system, space group
Unit cell dimensions
a
b
c
a
b
c
9.1849(5) Å
9.9521(5) Å
19.5774(12) Å
90.0°
102.830(2)°
90.0°
Volume
1744.87(17) Å3
4, 1.374 mg/m3
0.233 mmꢁ1
Z, calculated density
Absorption coefficient
F(000)
752
Crystal size
0.30 ꢂ 0.25 ꢂ 0.20 mm
Theta range for data collection
Limiting indices
Reflections collected/unique
Completeness to theta = 31.94
Absorption correction
Max. and min. transmission
Refinement method
Data/restraints/parameters
Goodness-of-fit on F2
Final R, RW (obs., data)
2.13–31.94°
Bond angle
ꢁ13 6 h 6 11, ꢁ11 6 k 6 14, ꢁ29 6 l 6 29
24214/5997
99.4%
Semi-empirical from equivalents
0.9548 and 0.8833
Full-matrix least squares on F2
5997/3/237
C(6)AC(1)AO(1)
C(6)AC(1)AC(2)
O(1)AC(1)AC(2)
C(1)AC(2)AC(30)
C(1)AC(2)AC(3)
C(30)AC(2)AC(3)
C(4)AC(3)AC(2)
C(4)AC(30)AC(2)
C(3)AC(4)AC(30)
C(3)AC(4)AC(5)
C(30)AC(4)AC(5)
O(2)AC(5)AC(6)
O(2)AC(5)AC(4)
C(6)AC(5)AC(4)
C(1)AC(6)AC(5)
C(1)AC(6)AC(7)
C(5)AC(6)AC(7)
C(6)AC(7)AC(8)
C(6)AC(7)AC(18)
C(8)AC(7)AC(18)
C(17)AC(8)AC(9)
C(17)AC(8)AC(7)
C(9)AC(8)AC(7)
C(8)AC(17)AO(1)
O(1)AC(17)AC(16)
C(18)AC(23)ACl(1)
C(22)AC(23)ACl(1)
C(1)AO(1)AC(17)
123.22(15)
126.14(15)
110.64(14)
112.0(3)
110.31(9)
36.8(4)
113.54(12)
115.9(5)
39.0(4)
1.043
0.0571, 0.1528
115.5(2)
117.9(3)
120.95(17)
121.13(18)
117.90(17)
118.78(15)
122.73(14)
118.47(14)
109.99(12)
109.29(13)
111.44(12)
117.53(14)
120.67(14)
121.80(13)
123.27(14)
113.34(14)
121.18(16)
117.41(17)
118.40(13)
NMR (CDCl3, 125 MHz, ppm) d: 196.8, 165.9, 147.6, 142.4, 133.0,
131.8, 131.7, 131.4, 129.9, 129.1, 128.4, 127.6, 127.1, 126.9,
124.9, 123.9, 117.5, 117.0, 114.7, 37.1, 33.0, 27.8, 20.4.
2.1.3. 12-(2-Nitrophenyl)-8,9,10,12-tetrahydrobenzo[a]xanthen-11-
one 3a
Pale yellow crystals, yield: 75%. m.p. 268–270 °C; IR (KBr,
cmꢁ1): 3070, 2949, 2860, 1650, 1594, 1530, 1370, 1225. 1H NMR
(CDCl3,300 MHz, ppm) d: 8.55–7.02 (m, 10H), 6.56 (s, 1H), 2.61–
2.70 (m, 2H), 2.34–2.61 (m, 2H), 1.85–2.06 (m, 2H). 13C NMR
(CDCl3, 75.46 MHz, ppm) d: 196.9, 165.4, 149.3, 148.2, 139.2,
132.7, 131.7, 131.5, 131.2, 129.7, 128.2, 127.5, 127.0, 125.2,
124.6, 124.4, 116.8, 116.2, 114.6, 36.7, 30.3, 27.7, 20.2.
2.1.6. 12-(4-Fluorophenyl)-8,9,10,12-tetrahydrobenzo[a]xanthen-11-
one 6a
2.1.4. 12-(3-Bromophenyl)-8,9,10,12-tetrahydrobenzo[a]xanthen-11-
one 4a
White crystals, yield: 70%. m.p. 216–218 °C; IR (KBr, cmꢁ1):
3079, 2947,2924, 2854, 1653,1593, 1503, 1372, 1222. 1H NMR
(CDCl3, 300 MHz, ppm) d: 8.35–6.82 (m, 10H), 5.75 (s, 1H), 2.49–
2.72 (m, 2H), 2.31–2.48 (m, 2H), 2.03–2.07 (m, 2H). 13C NMR
(CDCl3, 75 MHz, ppm) d: 196.9, 165.6, 165.5, 162.8, 159.6, 147.7,
140.8, 140.7, 131.5, 131.2, 129.9, 129.8, 128.4, 126.9, 124.9,
123.5, 117.4, 116.9, 115.4, 115.1, 114.8, 36.9, 33.9, 27.7, 20.2.
Pale yellow crystals, yield: 75%. m.p. 192–194 °C; IR (KBr,
cmꢁ1): 3053, 2950, 2885, 1650, 1592, 1565, 1371, 1184. 1H NMR
(CDCl3, 500 MHz, ppm) d: 7.94–7.06 (m, 10H), 5.75 (s, 1H), 2.74–
2.79 (m, 1H), 2.63–2.69 (m, 1H), 2.46–2.52 (m, 1H), 2.36–2.43
(m, 1H). 13C NMR (CDCl3, 125 MHz, ppm) d: 196.9, 165.9, 147.8,
147.3, 131.6, 131.4, 131.3, 131.2, 129.8, 129.6, 129.2, 128.5,
127.4, 127.2, 125.1, 123.5, 122.6, 117.1, 116.8, 114.9, 36.9, 34.5,
27.8, 20.2.
2.1.7. 12-(4-Methoxyphenyl)-8,9,10,12-tetrahydrobenzo[a]xanthen-
11-one 7a
White crystals, yield: 75%. m.p. 173–175 °C; IR (KBr, cmꢁ1):
3063, 2943, 2898, 2832, 1653, 1595, 1378, 1249, 1227. 1H NMR
(CDCl3, 500 MHz, ppm) d: 8.00–6.73 (m, 10H), 5.72 (s, 1H), 3.71
(s, 3H), 2.64–2.74 (m, 2H) 2.37–2.51(m, 2H), 2.00–2.08 (m, 2H).
13C NMR (CDCl3, 125 MHz, ppm) d: 197.2, 165.4, 157.8, 147.7,
137.4, 131.5, 131.4, 129.4, 128.7, 128.3, 126.9, 124.8, 123.7,
117.9, 115.7, 113.6, 55.1, 37.0, 33.7, 27.7, 20.3.
2.1.5. 12-(4-Chlorophenyl)-8,9,10,12-tetrahydrobenzo[a]xanthen-11-
one 5a
White crystals, yield: 75%. m.p. 197–199 °C; IR (KBr, cmꢁ1):
3061, 2956, 2927, 2887, 1655, 1593, 1370, 1227, 1189, 751. 1H
NMR (CDCl3, 400 MHz, ppm) d: 7.88–7.11 (m, 10H), 5.71 (s, 1H),
2.66–2.75 (m, 2H), 2.33–2.47 (m, 2H), 1.96–2.08 (m, 2H). 13C
NMR (CDCl3, 100 MHz, ppm) d: 196.9, 165.7, 147.7, 143.5, 131.9,
131.5, 131.2, 129.8, 129.0, 128.4, 128.5, 127.1, 125.0, 123.4,
117.0, 116.9, 115.1, 37.0, 34.1, 27.7, 20.2.
2.1.8. 12-(4-Tolyl)-8,9,10,12-tetrahydrobenzo[a]xanthen-11-one 8a
White crystals, yield: 80%. m.p. 198–200 °C; IR (KBr, cmꢁ1):
3041, 3018, 2946, 2895, 2832, 1650, 1595, 1373, 1225, 1186,

A. Sethukumar et al. / Journal of Molecular Structure 1008 (2012) 8–16
11
Fig. 1. 1H NMR spectrum of compound 8a.
814. 1H NMR (CDCl3, 500 MHz, ppm) d: 8.03–7.01 (m, 10H), 5.74 (s,
1H), 2.68–2.78 (m, 2H), 2.40–2.50 (m, 2H), 2.24 (s, 3H), 2.01–2.06
(m, 2H). 13C NMR (CDCl3, 125 MHz, ppm) d: 197.0, 165.5, 147.7,
142.2, 135.7, 131.5, 131.4, 129.0, 128.7, 128.3, 126.9, 124.8,
123.7, 117.9, 116.9, 115.7, 37.0, 34.2, 27.7, 21.0, 20.3.
2.68–2.74 (m, 1H), 2.58–2.65 (m, 2H), 2.26–2.33 (m, 1H), 2.09–
2.30 (m, 1H), 1.87–1.94 (m, 1H). 13C NMR (CDCl3, 125 MHz, ppm)
d: 178.5, 156.4, 149.3, 145.4, 131.3, 131.2, 128.7, 128.6, 128.3,
128.2, 126.7, 126.5, 124.6, 123.1, 117.3, 117.1, 111.3, 36.1, 26.9,
23.9, 19.9.
2.1.9. 12-(2,4-Dichlorophenyl)-8,9,10,12-tetrahydrobenzo[a]xanthen-
11-one 9a
2.2.2. 12-(2-Chorophenyl)-8,9,10,12-tetrahydrobenzo[a]xanthen-11-
one thiosemicarbazone 2b
White crystals, yield: 70%. m.p. 194–196 °C; IR (KBr,
cmꢁ1):3061, 2922, 2849, 1647, 1593, 818. 1H NMR (CDCl3,
300 MHz, ppm) d: 7.85–7.13 (m, 9H), 5.70 (s, 1H), 2.73–2.75 (m,
2H), 2.39–2.47 (m, 2H), 2.04–2.07 (m, 2H). 13C NMR (CDCl3,
75 MHz, ppm) d: 196.8, 165.9, 147.8, 145.1, 132.3, 131.5, 131.1,
130.3, 130.1, 129.4, 128.5, 128.0, 127.2, 125.1, 123.3, 116.9,
116.3, 114.6, 36.9, 34.0, 27.7, 20.2.
Pale yellow crystals, yield: 65%. m.p. 235–237 °C; IR (KBr,
cmꢁ1): 3408, 3347, 3277, 3163, 3046, 2923, 2853, 1650, 1600,
1494, 1233. 1H NMR (CDCl3, 500 MHz, ppm) d: 8.62–6.39 (m,
3H), 6.11 (s, 1H), 2.73–2.78 (m, 1H), 2.60–2.67 (m, 2H), 2.29–
2.36 (m, 1H), 2.04–2.10 (m, 1H), 1.85–1.90 (m, 1H). 13C NMR
(CDCl3, 125 MHz, ppm) d: 178.2, 157.2, 149.2, 147.8, 143.3,
131.4, 131.3, 131.2, 130.8, 129.6, 128.9, 128.5, 128.0, 127.8,
126.9, 124.7, 123.6, 117.8, 117.4, 111.6, 32.5, 29.7, 27.2, 24.3, 19.7.
2.2. General procedure for the preparation of compounds 1b–5b
2.2.3. 12-(3-Bromophenyl)-8,9,10,12-tetrahydrobenzo[a]xanthen-11-
one thiosemicarbazone 3b
To a boiling solution of 1a, 2a, 4a, 6a and 8a (1.0 mmol) in
methanol-chloroform (1:1, 40 mL), thiosemicarbazide (1.5 mmol)
and few drops of acetic acid were added and refluxed for 24 h on
a water bath. After cooling, the separated solid was filtered off
and purified by column chromatography using benzene and ethyl
acetate (9.5:0.5) as eluent. The separated fractions were allowed
to dry and the obtained solids were recrystallized using ethanol
as solvent.
Pale yellow crystals, yield: 73%. m.p. 218–220 °C; IR (KBr,
cmꢁ1): 3418, 3363, 3225, 3133, 3035, 2943, 1654, 1588, 1501,
1475, 1232. 1H NMR (DMSO, 500 MHz, ppm) d: 9.86–7.08 (m,
13H), 6.03 (s, 1H), 2.61–2.71 (m, 2H), 2.54–2.56 (m, 1H) 2.32–
2.38 (m, 1H), 1.84–1.89 (m, 1H), 1.66–1.71 (m, 1H). 13C NMR
(CDCl3, 125 MHz, ppm) d: 178.6, 155.8, 149.3, 149.0, 147.7, 131.6,
131.2, 131.2, 130.5, 129.4, 129.3, 128.8, 127.8, 127.2, 125.1,
124.5, 121.7, 117.7, 117.4, 111.6, 34.6, 26.9, 24.7, 20.3.
2.2.1. 12-(Phenyl)-8,9,10,12-tetrahydrobenzo[a]xanthen-11-one
thiosemicarbazone 1b
Pale yellow crystals, yield: 68%. m.p. 188–191 °C; IR (KBr,
cmꢁ1): 3227, 3073, 3013, 2958, 2887, 1660, 1585, 1231, 1012. 1H
NMR (CDCl3, 500 MHz, ppm) d: 8.70–6.43 (m, 14H), 5.71 (s, 1H),
2.2.4. 12-(4-Fluorophenyl)-8,9,10,12-tetrahydrobenzo[a]xanthen-11-
one thiosemicarbazone 4b
Pale yellow crystals, yield: 65%. m.p. 238–240 °C; IR (KBr,
cmꢁ1): 3426, 3352, 3232, 3148, 3041, 2937, 2865, 1656, 1596,

12
A. Sethukumar et al. / Journal of Molecular Structure 1008 (2012) 8–16
Fig. 2. 13C NMR spectrum of compound 8a.
1226, 837. 1H NMR (DMSO, 500 MHz, ppm) d: 9.90–6.95 (m, 13H),
6.04 (s, 1H), 2.67–2.72 (m, 1H), 2.59–2.65 (m, 1H), 2.54–2.56 (m,
1H), 2.32–2.38 (m, 1H), 1.85–1.89 (m, 1H) 1.67–1.70 (m, 1H). 13C
NMR (CDCl3, 125 MHz, ppm) d: 178.6, 161.7, 159.8, 155.6, 149.3,
147.7, 142.9, 142.8, 132.2, 130.6, 130.5, 129.1, 128.8, 127.1,
125.0, 124.7, 117.9, 117.7, 115.1, 114.9, 111.9, 34.1, 26.9, 24.7,
20.3.
rier difference syntheses (SHELXS-97) [30] and refined by full ma-
trix least square procedure on F2 with anisotropic thermal
parameters. All non-hydrogen atoms were refined (SHELXL-97)
[31] and placed at chemically acceptable positions. A total of 237
parameters were refined with 5997 unique reflections which cov-
ered the residuals to R1 = 0.0571. Crystallographic data have been
deposited with the Cambridge Crystallographic Data Centre as sup-
plementary publication number CCDC 809606 for 2a. Copies of the
data can be obtained free of charge via http://www.ccdc.cam.ac.uk/
conts/retrieving.html, or from the Cambridge Crystallographic
Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: (+44)
1223 336 033: or e-mail: deposit@ccdc.cam.ac.uk.
2.2.5. 12-(4-Tolyl)-8,9,10,12-tetrahydrobenzo[a]xanthen-11-one
thiosemicarbazone 5b
Pale yellow crystals, yield: 70%. m.p. 194–196 °C; IR (KBr,
cmꢁ1): 3418, 3358, 3257, 3144, 3035, 3051, 2928, 2865, 1654,
1586, 1501, 1233, 1086. 1H NMR (DMSO, 500 MHz, ppm) d:
8.61–6.33 (m, 13H), 5.67 (s, 1H), 2.68–2.72 (m, 1H) 2.57–2.65 (m,
2H), 2.26–2.31 (m, 1H), 2.22 (s, 3H), 1.92–2.08 (m, 1H). 13C NMR
(CDCl3, 125 MHz, ppm) d: 178.7, 156.3, 149.2, 147.4, 142.4, 136.0,
131.3, 131.2, 129.0, 128.6, 128.5, 128.3, 128.1, 126.7, 124.5,
123.1, 117.2, 111.4, 35.7, 26.8, 23.8, 20.9, 19.9.
3. Results and discussion
In the present study
a series of 12-aryl-8,9,10,12-tetra-
hydrobenzo[a]xanthen-11-ones [1a–9a] were prepared using
BF3ꢀOEt2 as catalyst. In this synthetic procedure the difficulty in
separation of catalyst from the reaction mixture was completely
avoided and also both the electron rich and electron deficient aryl
aldehydes undergo the reaction conveniently. Thiosemicarbazone
derivatives [1b–5b] were also prepared in the presence of acid
catalyst.
2.3. X-ray crystallography
Crystal was grown by slow evaporation technique using ethanol
as solvent. Diffraction data were collected on a Bruker, 2004 APEX
2 diffractometer using graphite-monochromated Mo K
a radiation
(k = 0.71073 Å) at 293 K with crystal size of 0.30 ꢂ 0.25 ꢂ
0.20 mm. Crystal data and structure refinement details are given
in Table 1. Selected bond distances and angles are given in Table
2. The structure was solved by direct methods and successive Fou-
3.1. IR spectral analysis of compounds 1a–9a
For 1a–9a the observed maxima in the region of 1647–
1655 cmꢁ1 are characteristic for carbonyl (C@O) stretching

A. Sethukumar et al. / Journal of Molecular Structure 1008 (2012) 8–16
13
Fig. 3. 1H NMR spectrum of compound 5b.
frequencies of
a,b-unsaturated ketones. Similarly, the C@C stretch-
3.3. NMR spectra
ing frequencies associated with the
a
,b-unsaturated ketones are
observed in the region of 1592–1595 cmꢁ1 as reported earlier [9].
The CAH stretching vibration bands are observed in the region of
2832–3063 cmꢁ1. In all the cases the weak aromatic CAH bands
3.3.1. 1H NMR spectral analysis of compound 8a
1H NMR spectrum of compound 8a (Fig. 1) exhibit three multi-
plets in the region of 2.01–2.78 ppm (2.04, 2.44 and 2.72 ppm). A
signal appeared at 2.72 ppm is assigned to Ha and Hb protons at
C-8 carbon. The remaining two multiplets at 2.44 and 2.04 ppm
are assigned to protons (Ha and Hb) at C-10 and C-9 carbons,
respectively. The benzylic proton at C-12 resonated at 5.74 ppm
as a singlet with one proton integral value. The aromatic protons
appeared in the region of 7.01–8.03 ppm. A sharp singlet appeared
at 2.24 ppm is assigned to the methyl substituent at para-position
of phenyl group.
are obtained in the region of 3018–3063 cmꢁ1
.
3.2. IR spectral analysis of compounds 1b–5b
Earlier studies [32] indicated that the characteristic vibrational
bands observed around 1645 cmꢁ1 is due to C@N stretching fre-
quency of thiosemicarbazone moiety. Similarly, thiosemicarbazone
derivatives of xanthones (1b–5b) also show the C@N stretching
frequency in the region of 1650–1654 cmꢁ1. The strong absorption
band observed about 3300 cmꢁ1 in the IR spectrum is normally as-
signed to NAH stretching mode of amines. In 1b–5b, the character-
istic IR bands in the region 3257 and 3277 cmꢁ1 are due to NAH
stretching frequency of the thiosemicarbazone moiety. Generally,
the absorption arising from the aromatic and aliphatic CAH
stretching frequencies occur in the general region 3075–
2775 cmꢁ1. In 1b–5b also the similar absorption bands are noted
3.3.2. 13C NMR spectral analysis of compound 8a
13C NMR spectrum of compound 8a is shown in Fig. 2. In gen-
eral, the aromatic carbons could be readily distinguished from
the other carbons due to their characteristic absorption in the re-
gion of 120–140 ppm. For 8a, the aromatic carbon signals appeared
in the range of 115.7–147.7 ppm. Two less intense signals in the
higher frequency region (197.0 and 165.50 ppm) are assigned to
carbonyl sp2 carbon and C-7a carbon, respectively. 13C NMR spec-
trum of compound 8a showed four signals in the aliphatic region.
The signals at 27.7, 34.2 and 20.3 ppm are due to C-10, C-8 and C-9
carbons, respectively. The deshielded signal (34.2 ppm) is assigned
to methylene carbon at C-8. The other two signals at 27.7 and
20.3 ppm are assigned to C-10 and C-9 carbons, respectively. The
shielding chemical shift differences between C-8 and C-10 carbons
in the region 3051–2928 and 3046–2853 cmꢁ1
, respectively.
Hence, these stretching frequencies can be ascribed to aromatic
and aliphatic CAH stretching frequencies. Wiles et al. [33] reported
that the C@S stretching vibrations of several thiosemicarbazones
exhibit a band at 1135 cmꢁ1 and for 1b–5b also, an intense absorp-
tion band is observed in the region of 1193 cmꢁ1, respectively due
to C@S stretching.

14
A. Sethukumar et al. / Journal of Molecular Structure 1008 (2012) 8–16
Fig. 4. 13C NMR spectrum of compound 5b.
are about 6.5 ppm. The methine carbon (C-12) is slightly deshield-
ed and obtained at 37.0 ppm.
19.9, 23.8 and 26.8 ppm are assigned to methylene carbons at C-
9, C-10 and C-8 positions. The methine carbon (C-12) signal is ob-
served at 35.7 ppm. The signal observed at 20.9 ppm is due to
methyl carbon at para-position of phenyl group. The disappearance
of carbonyl carbon signal (around 195 ppm) and the appearance of
two new signals at 178.7 (C@S) and 156.3 ppm (C@N) corroborates
the formation of compound 5b.
3.3.3. 1H NMR spectral analysis of compound 5b
1H NMR spectrum of compound 5b (Fig. 3) showed a multiplet
in the range 6.99–8.12 ppm which corresponds to 10 protons and
is attributed to aromatic protons. The three multiplets appeared
at 1.99, 2.43 and 2.66 ppm are assigned to Ha and Hb protons at-
tached to C-9, C-10 and C-8 carbons, respectively. Moreover, the
observed two sharp singlets at 2.22 and 5.67 ppm are assigned to
methyl substituent at para-position of phenyl ring and benzylic
proton at C-12, respectively. A broad singlet at 6.33 ppm with
one proton integration is due to NH proton of thiosemicarbazone
moiety. Similarly, a sharp singlet observed at 8.61 ppm is conve-
niently assigned to one of the ANH2 protons. The signal due to an-
other proton in ANH2 group might be merged with the aromatic
proton signals. This is also supported by the observation of higher
integral values for the aromatic protons.
3.3.5. HSQC spectral analysis of compound 5b
From the 1H–13C COSY spectrum of 5b (Fig. 5), the following
important assignments can be made in the aliphatic region: The
two multiplets at 1.92 and 2.06 ppm show cross peak with the sig-
nal at 19.9 ppm. This suggests that the carbon signal is due to C-9
carbon. Likewise, the other two multiplets at 2.28 and 2.58 ppm
show cross peak with the carbon signal at 23.8 ppm and it suggests
that the carbon signal is due to C-10 carbon whereas, the remain-
ing multiplets at 2.70 and 2.63 ppm show cross peak with the sig-
nal at 26.8 ppm denotes that the signal is due to C-8 carbon.
Similarly, two singlets at 5.57 and 2.22 ppm show cross peaks with
the carbon signals at 35.7 and 20.9 ppm, respectively. It infers that
the carbon signals are due to benzylic carbon (C-12) and CH3 car-
bon present in the phenyl group. The assignment of ANHA proton
signal (at 6.33 ppm) and one of the ANH2 protons signal (at
8.61 ppm) from 1H NMR spectrum is confirmed unambiguously
by HSQC spectral analysis as there are no correlations for the above
mentioned signals. In the higher frequency region of the 13C spec-
trum, apart from the C@S signal at 178.7 ppm there are eight sig-
nals without correlations respectively at 156.3, 149.2, 147.4,
3.3.4. 13C NMR spectral analysis of compound 5b
13C NMR spectrum of compound 5b is shown in Fig. 4. The 13C
NMR spectral assignment has been made based on characteristic
signal positions of the functional groups and comparison with
those of parent compound. In 13C NMR spectrum of compound
5b, the signals appeared in the range 111.4–147.4 ppm are due
to aromatic carbons. The less intense signals resonated in the
deshielded region of 178.7 and 156.3 ppm are assigned to C@S
and C@N carbons, respectively. The three signals appeared at

A. Sethukumar et al. / Journal of Molecular Structure 1008 (2012) 8–16
15
Fig. 5. HSQC spectrum of compound 5b.
Fig. 6. ORTEP diagram of 2a.

16
A. Sethukumar et al. / Journal of Molecular Structure 1008 (2012) 8–16
142.4, 136.0, 131.3, 131.2 and 111.4 ppm. Among the eight signals
the deshielded signals at 149.2 and 147.4 ppm are conveniently as-
disorder was observed for C-3 and the protons attached to it. The
protons attached to C-2 and C-4 were also positionally disordered
over two positions. Cyclohexenone ring exhibit envelope confor-
mation, with slightly more pronounced puckering of the C(3) atom
by 0.546 Å from the C(2)/C(1)/C(6)/C(5)/C(4) plane [similarly, C(30)
is also deviates from the C (2)/C(1)/C(6)/C(5)/C(4) plane to the ex-
tent of 0.412 Å].
signed to C-7a and C-6a carbons respectively as they are
a to elec-
tronegative oxygen. Similarly, the signal which is comparatively
shielded (111.4 ppm) is due to olefinic carbon at C-11a. The signals
at 142.4 and 136.0 ppm might be due to the ipso carbons of 4-
methylphenyl ring. The remaining signals at 131.3 and
131.2 ppm are assigned to C-4a and C-1a carbons, respectively.
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3.4. Single crystal X-ray structural analysis of 12-(2-chlorophenyl)-
8,9,10,12-tetrahydrobenzo[a]xanthen-11-one (2a)
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monoclinic space group P21/n with four discrete molecules in the
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can be described as ‘‘flattened boat’’ which is evidenced from the
small puckering parameters coupled with the O(1) and C(7) atoms
present at 1st and 4th positions respectively of the pyran ring. The
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attached to C-2 and C-4 were also positionally disordered over two
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4. Conclusions
A series of tetrahydrobenzo[a]xanthen-11-ones (1a–9a) have
been synthesized by the MCR of 2-naphthol, aryl aldehyde and
1,3-cyclohexanedione using BF3:OEt2 as a catalyst. Thiosemicarba-
zone derivatives (1b–5b) were also derived and the synthesized
compounds were characterized by IR, 1D and 2D-NMR spectra.
From the single crystal XRD analysis of 2a the conformation of
the pyran ring can be described as ‘‘flattened boat’’. Positional
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