One-pot synthesis and UV-Visible absorption studies of novel tricyclic heterocycle tethered Xanthene-1,8-diones

Article abstract of DOI:10.1007/s12039-015-0835-9

Abstract A series of new tricyclic heterocyclic xanthene-1,8-diones tethered with chromophoric dibenzo [b, d]furan, dibenzo[b, d]thiophene and 9-methyl-9H-carbazoles were synthesized through one-pot condensation of dibenzo[b, d]furan-2-carbaldehyde, dibenzo[b, d] thiophene-2-carbaldehyde and 9-methyl-9H-carbazole-3-carbaldehyde with cyclic 1,3-dicarbonyls in the presence of recyclable PPA-SiO₂ catalyst under solvent-free conditions. Further, UV-Visible absorption properties of all the synthesized compounds were investigated in CHCl₃, THF and acetonitrile. [Figure not available: see fulltext.]

Full text of DOI:10.1007/s12039-015-0835-9

c
J. Chem. Sci. Vol. 127, No. 5, May 2015, pp. 803–810. ꢀ Indian Academy of Sciences.
DOI 10.1007/s12039-015-0835-9
One-pot synthesis and UV-Visible absorption studies of novel tricyclic
heterocycle tethered Xanthene-1,8-diones
THIRUMAL YEMPALAa, BALASUBRAMANIAN SRIDHARb and SRINIVAS KANTEVARIa,∗
aCPC Division (Organic Chemistry Division-II), CSIR-Indian Institute of Chemical Technology,
Hyderabad 500 007, India
bCentre for X-ray Crystallography, CSIR-Indian Institute of Chemical Technology, Hyderabad 500 007, India
e-mail: kantevari@yahoo.com; kantevari@gmail.com
MS received 07 July 2014; revised 28 December 2014; accepted 29 December 2014
Abstract. A series of new tricyclic heterocyclic xanthene-1,8-diones tethered with chromophoric dibenzo
[b, d]furan, dibenzo[b, d]thiophene and 9-methyl-9H-carbazoles were synthesized through one-pot con-
densation of dibenzo[b, d]furan-2-carbaldehyde, dibenzo[b, d] thiophene-2-carbaldehyde and 9-methyl-9H-
carbazole-3-carbaldehyde with cyclic 1,3-dicarbonyls in the presence of recyclable PPA-SiO2 catalyst under
solvent-free conditions. Further, UV-Visible absorption properties of all the synthesized compounds were
investigated in CHCl3, THF and acetonitrile.
Keywords. Xanthenediones; Dibenzo[b, d]furan; 9-Methyl carbazole; Dibenzo[b, d]thiophene; One-pot
synthesis; UV-Visible absorption studies.
1. Introduction
light-emitting diodes and electron-transport materials
or electron-transport-type host materials because of its
high triplet energy and strong electron-withdrawing
oxygen linkage in its molecular structure.9b−c More-
over, all these heterocycles dibenzofuran, carbazole
and benzothiophene are naturally abundant with more
pronounced anti-bacterial, anti-depressant, and anti-
tuberculosis activities.10a−d
In recent years xanthene derivatives have attracted sci-
entists world over due to their promising applications in
medicinal and material chemistry.1–5 Among this class,
xanthenediones play a vital role as the key structural
unit in a variety of natural products exhibiting several
biological activities.3–5 Due to the presence of in-built
pyran ring architecture and their extended conjugation
with aromatic groups, xanthenediones exhibit applica-
tions in optoelectronic materials.They form an important
component in laser dyes6 and are used in laser technol-
ogies7 for photodynamic therapy. Xanthenediones are
also used as pH sensitive fluorescent materials for visu-
alization of biomolecules.8 In view of the importance
of xanthenediones, we would like to extend the con-
jugation within the xanthenedione moiety by replacing
the simple/substituted phenyl groups with tricyclic het-
erocycles.
For the past decade, tricyclic systems such as diben-
zofuran, dibenzothiophene and carbazole with planar
architecture9a have got significant interest in the area
of materials, dyes, photochemistry, and light-emitting
diodes. They also act as ideal conjugated units for the
construction of organic semiconductors. Among these
three heterocycles, dibenzofuran has been used as an
effective organic material for phosphorescent organic
2. Experimental
2.1 General remarks
Melting points were measured with a Fischer-Johns
melting point apparatus and are uncorrected. IR spectra
were recorded as KBr pellets and absorptions are
reported in cm−1. NMR spectra were recorded on 300
(Bruker) and 500 MHz (Varian) spectrometers in appro-
priate solvents using TMS as internal standard and
the chemical shifts are shown in δ scales. 13C NMR
spectra were recorded on 75 MHz spectrometers. High-
resolution mass spectra were obtained by using ESI-
QTOF mass spectrometry. All the experiments were
monitored by analytical thin layer chromatography
(TLC) performed on silica gel GF254 pre-coated plates.
After elution, the plate was visualized under UV illu-
mination at 254 nm for UV active materials. Silica
gel finer than 200 mesh was used for column chro-
matography. Yields refer to chromatographically and
∗For correspondence
803

804
Thirumal Yempala et al.
spectroscopically homogeneous materials, unless other- 2.3b 9-(Dibenzo[b,d]furan-2-yl)-3,3,6,6-tetramethyl-3,
wise stated. Appropriate names for all the new com- 4,5,6,7,9-hexahydro-1H-xanthene-1,8(2H)-dione (7a):
pounds were given with the help of ChemBioOffice White solid; yield: 404 mg (92%); M.p. 190–195◦C.
12.0; 2010. All the photophysical properties for these IR (KBr): 2955, 2927, 1661, 1622, 1448, 1431, 1360,
compounds were recorded with JASCO 500 UV Spec- 1200, 1166, 1138, 1002, 746 cm−1. 1H NMR (300 MHz,
trophotometer. All the graphs were drawn using Origin CDCl3): δ 7.94 (d, J = 6.9 Hz, 1 H), 7.88 (d, J = 1.7 Hz,
software version 7.0. The solvents for column elution 1 H), 7.46 (d, J = 8.1 Hz, 1 H), 7.41–7.31 (m, 2 H),
were purchased commercially and for UV-visible stud- 7.29–7.22 (m, 2 H), 4.86 (s, 1 H), 2.48 (s, 4 H),
ies the solvents were purchased from Sigma Aldrich.
2.25–2.10 (m, 4 H), 1.12 (s, 6 H), 1.01 (s, 6 H). 13C
NMR (75MHz, CDCl3): δ 196.4, 162.1, 156.4, 154.8,
138.8, 127.2, 126.7, 123.5, 122.4, 120.8, 115.8, 111.3,
111.0, 50.7, 40.8, 31.7, 29.2, 27.2. HRMS (ESI): m/z
[M+Na]+ calcd for C29H28O4Na: 463.1885; found:
463.1887.
2.2 General procedure for the synthesis of aldehydes
2a, 2b and 2c
All these aldehydes were synthesized according to the
procedure described in literature.11a Analytical data is
in agreement with the literature data for dibenzo[b, d]
furan-2-carbaldehyde (2a),11a 9-methyl-9H-carbazole-
3-carbaldehydes (2b)11a and dibenzo[b, d]thiophene-2-
carbaldehyde (2c).9
Spectral data of compound 2c: Light yellow solid;
yield: 60%; M.p. 61–63◦C. 1H NMR (300 MHz,
CDCl3): δ 10.13 (s, 1 H), 8.59 (t, J = 0.7 &1.3Hz, 1 H),
8.27–8.13 (m, 1 H), 8.00–7.90 (m, 2 H), 7.89–7.82 (m,
1 H), 7.55–7.43 (m, 2 H).
2.3c 9-(Dibenzo[b,d]furan-2-yl)-3,6-diisopropyl-3,4,5,
6,7,9-hexahydro-1H-xanthene-1,8 (2H)-dione (8a): Pale
yellow solid; yield: 439 mg (94%); M.p. 200–205◦C.
IR (KBr): 2960, 2874, 1674, 1623, 1476, 1448, 1371,
1353, 1243, 1189, 1136, 1023, 989, 841, 761 cm−1.
1H NMR (300 MHz, CDCl3): δ 8.00–7.91 (m, 1 H),
7.88–7.78 (dd, J = 8.8Hz & 1.7Hz, 1 H), 7.46 (d, J =
7.9Hz, 1 H), 7.42–7.31 (m, 2 H), 7.30–7.21 (m, 2 H),
4.87 (d, J = 3.0Hz, 1 H), 2.71–2.27 (m, 6 H), 2.17-1.80
(m, 4 H), 1.70–1.52 (m, 2 H), 1.04–0.90 (m, 12 H).
13C NMR (75MHz, CDCl3): δ 196.9, 163.5, 156.3,
154.8, 138.9, 127.4, 126.7, 124.2, 123.8, 122.3, 120.8,
116.6, 116.3, 111.3, 111.0, 41.3, 40.8, 38.7, 31.7, 30.8,
19.4. HRMS (ESI): m/z [M+H]+calcd for C31H33O4:
469.2378; found: 469.2361.
2.3 General procedure for the synthesis of
Xanthenediones
A mixture of aldehyde (1 mmol), diketone (2 mmol)
and PPA-SiO2 (20 mol%) were heated at 125◦C with
stirring for the time specified in table 2. After comple-
tion, the reaction mixture was cooled to room temper-
ature, and dichloromethane was added and the catalyst
was filtered off. The filtrate thus obtained was concen-
trated under vacuum. Recrystalization of crude mass in
CHCl3: hexane (1:5) yielded pure xanthenediones 6, 7
& 8 as crystalline solids.
2.3d 9-(9-Methyl-9H-carbazol-3-yl)-3,4,5,6,7,9-hexahydro-
1H-xanthene-1,8(2H)-dione (6b): White solid; yield:
361 mg (91%); M.p. 190–195◦C. IR (KBr): 2926, 1734,
1668, 1622, 1432, 1358, 1201, 1177, 1131, 1009, 959,
765, 700 cm−1. 1H NMR (300 MHz, CDCl3): δ 8.04 (d,
J = 8.3Hz, 1 H), 7.85 (s, 1H), 7.41 (d, J = 8.3 Hz, 1 H),
7.34 (t, J = 8.3Hz, 1 H), 7.28–7.22 (m, 1 H), 7.21–7.16
(d, J = 8.3Hz,1 H),7.12 (t, J = 7.2Hz,1 H), 4.92 (s,1H),
3.77 (s, 3 H), 2.74–2.51 (m, 4 H), 2.45–2.26 (m, 4 H),
2.06–1.97 (m, 4 H). 13C NMR (75MHz, CDCl3): δ
196.8, 163.6, 141.2, 135.4, 126.6, 125.4, 122.7, 122.5,
120.4, 119.9, 118.5, 117.5, 108.2, 107.9, 37.0, 31.5,
29.0, 27.2, 20.3. HRMS (ESI): m/z [M+Na]+calcd for
C26H23O3NNa: 420.1575; found: 420.1570.
2.3a 9-(Dibenzo[b,d]furan-2-yl)-3,4,5,6,7,9-hexahydro-
1H-xanthene-1,8(2H)-dione (6a): Yellow solid; yield:
364 mg (95%); M.p. 198–200◦C. IR (KBr): 2925, 1672,
1621, 1478, 1430, 1359, 1200, 1176, 1129, 1010, 956,
755 cm−1. 1H NMR (300 MHz, CDCl3): δ 7.95 (d, J =
7.7 Hz, 1 H), 7.86 (d, J = 1.5Hz, 1 H), 7.45 (d, J =
8.1 Hz, 1 H), 7.40–7.32 (m, 2 H), 7.31–7.22 (m, 2 H),
4.91 (s, 1 H), 2.74–2.50 (m, 4 H), 2.40–2.23 (m, 4 H),
2.11–1.94 (m, 4 H). 13C NMR (75MHz, CDCl3): δ 2.3e 3,3,6,6-Tetramethyl-9-(9-methyl-9H-carbazol-3-
196.6, 163.8, 156.4, 154.9, 139.1, 127.4, 126.8, 123.9, yl)-3,4,5,6,7,9-hexahydro-1H-xanthene-1,8 (2H)-dione
123.6, 122.4, 120.8, 120.7, 117.1, 111.4, 111.1, 36.9, (7b): Brown solid; yield: 421 mg (93%); M.p. 220–
31.6, 27.1, 20.2. HRMS (ESI): m/z [M+H]+ calcd for 223◦C. IR (KBr): 3324, 2968, 2918, 1701, 1612, 1598,
C25H21O4: 385.1439; found: 385.1446.
1513, 1452, 1283, 1164, 1127, 1015, 836, 694 cm−1.

Synthesis and absorption studies of Xanthene-1,8-diones
805
1H NMR (300 MHz, CDCl3): δ 8.02 (d, J =7.7 Hz, 1H),
7.86 (s, 1 H), 7.46–7.29 (m, 2 H), 7.28–7.17 (m, 2 H),
7.11 (t, J = 8.1Hz, 1 H), 4.87 (s, 1 H), 3.79 (s, 3 H),
2.48 (s, 4 H), 2.28–2.07 (m, 4 H), 1.12 (s, 6 H), 1.00
(s, 6 H). 13C NMR (75MHz, CDCl3): δ 196.5, 161.8,
141.1, 139.81, 135.17, 126.6, 125.2, 122.7, 120.2,
119.8, 118.4, 116.2, 108.2, 107.8, 50.7, 40.8, 32.2,
31.6, 29.2, 27.3. HRMS (ESI): m/z [M+Na]+calcd for
C30H31O3NNa: 476.2201; found: 476.2196.
2.3i 9-(Dibenzo[b,d]thiophen-2-yl)-3,6-diisopropyl-3,
4,5,6,7,9-hexahydro-1H-xanthene-1,8 (2H)-dione (8c):
Brick red solid; yield: 454 mg (94%); M.p. 80–85◦C.
IR (KBr): 2958, 1670, 1624, 1466, 1430, 1368, 1185,
1137, 819, 762, 733 cm−1. 1H NMR (300 MHz, CDCl3):
δ 8.16(s,1H),8.05(d, J=10.7Hz,1H),7.74(d, J=8.1Hz,
1H),7.69–7.63 (m,1H),7.46–7.17(m,3H),4.88(s,1H),
2.73–2.20 (m, 6 H), 2.17–1.76 (m, 4 H), 1.68–1.42 (m,
2 H), 1.04–0.75 (m, 12 H). 13C NMR (75MHz, CDCl3):
δ 196.8, 164.2, 140.7, 139.6, 137.5, 135.4, 129.1, 127.1,
127.0, 126.3, 124.0, 122.5, 122.3, 121.7, 121.6, 116.1,
41.3, 40.8, 38.7, 31.7, 31.0, 19.4. HRMS (ESI): m/z
[M+Na]+calcd for C31H32O2SNa: 507.1969; found:
507.1995.
2.3f 3,6-Diisopropyl-9-(9-methyl-9H-carbazol-3-yl)-
3,4,5,6,7,9-hexahydro-1H-xanthene-1,8(2H)-dione (8b):
Black solid; yield: 442 mg (92%); M.p. 120–124◦C.
IR (KBr): 2958, 1662, 1492, 1471, 1370, 1186, 1138,
1
744 cm−1. H NMR (300 MHz, CDCl3): δ 8.08–8.00
(m, 1 H), 7.85–7.75 (m, 1 H), 7.45–7.29 (m, 2 H),
7.27–7.07 (m, 3 H), 4.87 (d, J = 4.1Hz, 1 H), 3.78
(s, 3 H), 2.84–2.21 (m, 6 H), 2.16–1.75 (m, 4 H),
1.69–1.49 (m, 2 H), 1.02–0.86 (m, 12 H). 13C NMR
(75 MHz, CDCl3): δ 197.0, 163.9, 141.2, 138.0,
133.9, 126.7, 126.6, 125.3, 120.4, 120.3, 119.8, 118.4,
117.1, 108.2, 107.9, 41.5, 40.9, 38.8, 31.8, 31.1,
29.7, 19.4. HRMS (ESI): m/z [M+Na]+calcd for
C32H35O3NNa:504.2514; found: 504.2525.
3. Results and Discussion
Inspired by the applications of dibenzo[b, d]furan (1a),
9-methyl-9H-carbazole (1b), dibenzo[b, d]thiophene
(1c), and xanthenediones we envisaged to combine xan-
thenedione and tricyclic heterocycles in one molecular
frameto examine their photophysical properties. In con-
tinuation of our work,11 we herein describe an efficient
one-pot synthesis of dibenzofuran, dibenzothiophene
and 9-methyl-9H-carbazoles embedded xanthene-1,8-
diones through the condensation of respective alde-
hydes with active cyclic1,3-dicarbonyl in presence of
PPA-SiO2 catalyst. UV-Visible absorption properties
are evaluated for these new derivatives.
Initiating the study, dibenzo[b, d]furan-2-carbalde-
hyde (2a), 9-methyl-9H-carbazole-3-carbaldehyde (2b)
and dibenzo[b,d]thiophene-2-carbaldehyde (2c) required
were synthesized using formylation conditions devel-
oped in our laboratory (scheme 1).11a For example, the
reaction dibenzo[b, d]furan with α, α-dichloromethyl
methyl ether and SnCl4 at room temperature in dichlo-
romethane gave the required dibenzo[b, d]furan-2-
carbaldehyde(2a)in84%yield. Similarly 9-methyl-9H-
carbazole and dibenzo[b, d]thiophene was formylated
toobtain 9-methyl-9H-carbazole-3-carbaldehyde (2b) and
dibenzo[b, d]thiophene-2-carbaldehyde (2c) respectively
in 80% and 60% yields. All the aldehydes 2a-c was
fully characterized by 1H and 13C NMR spectral analy-
sis and are in agreement with reported data.9,11a
2.3g 9-(Dibenzo[b,d]thiophen-2-yl)-3,4,5,6,7,9-hexahydro-
1H-xanthene-1,8(2H)-dione (6c): White solid; yield:
372 mg (93%); M.p. 210–213◦C. IR (KBr): 2926, 1734,
1668, 1622, 1432, 1358, 1201, 1177, 1131, 1009, 959,
1
765, 700 cm−1. H NMR (300 MHz, CDCl3): δ 8.20–
8.14(m,1H),8.06(d, J =1.5Hz,1H),7.78–7.71(m,1H),
7.69–7.63 (m, 1 H), 7.42–7.32 (m, 2 H), 7.31–7.26 (m,
1 H), 4.93 (s, 1 H), 2.74–2.49 (m, 4 H), 2.40–2.22 (m,
4 H), 2.11–1.91 (m, 4 H). 13C NMR (75MHz, CDCl3):
δ 196.5, 163.9, 140.9, 139.6, 137.4, 135.4, 129.9,
127.1, 126.3, 124.0, 122.5, 122.3, 121.6, 116.8, 36.8,
31.6, 27.0, 20.2. HRMS (ESI): m/z [M+H]+calcd for
C25H21O3S: 401.1211; found: 401.1206.
2.3h 9-(Dibenzo[b,d]thiophen-2-yl)-3,3,6,6-tetramethyl-
3,4,5,6,7,9-hexahydro-1H-xanthene-1,8 (2H)-dione (7c):
Pale yellow solid; yield: 414 mg (91%); M.p. 200–
204◦C. IR (KBr): 2957, 2916, 1656, 1621, 1464, 1429,
1359, 1200, 1165, 1136, 1003, 763, 735cm−1. 1H NMR
(300 MHz, CDCl3): δ 8.19 (m, 1 H), 8.07 (d, J = 1.3Hz,
1 H), 7.80–7.70 (m, 1 H), 7.69–7.62 (d, J = 8.3Hz,
1H), 7.42–7.26 (m, 3 H), 4.88 (s, 1 H), 2.48 (s, 4 H),
2.25–2.08 (ab d, 4 H), 1.12 (s, 6 H), 1.00 (s, 6 H). 13
C
NMR (75MHz, CDCl3): δ 196.4, 162.2, 140.6, 139.6,
135.4, 129.4, 127.1, 126.3, 124.0, 122.6, 122.3, 121.7,
121.6, 115.6, 50.6, 40.8, 31.8, 29.2, 27.2. HRMS (ESI):
m/z [M+H]+calcd for C29H29O3S: 457.1837; found:
457.1845.
Scheme 1. Preparation of tricyclic heterocyclic aldehydes
2a–c.

806
Thirumal Yempala et al.
Table 1. Optimization of reaction conditions for a selective reaction between aldehyde 2a
and compound 3.
S. No
Catalyst
mol%
Temp (◦C)
Time (h)
Yield (%)b
1
2
3
4
5
6
7
8
CH3SO3H
p−TSA
100
20
20
20
20
20
20
20
20
20
20
20
20
30
20
30
12
6
12
6
46
70
50
66
78
63
53
41
54
26
45
38
62
86
95
125
125
125
125
125
125
125
125
30
125
125
100
125
125
Montmorillonite-K10
HClO4-SiO2
H2SO4-SiO2
InCl3. 3H2O
FeCl3.6H2O
LiBr
6
12
12
12
12
12
6
12
6
4
9
Fe2(SO4)3.7H2O
SnCl2.2H2O
SnCl2.2H2O
K5CoW12O40.3H2O
PPA-SiO2
10
11
12
13
14
15
PPA-SiO2
PPA-SiO2
1.5
(a) Dibenzo[b, d]furan-2-carbaldehyde (2a) (1 mmol), 1,3-cyclohexane dione 3 (2 mmol),
and catalyst were mixed and conducted the reaction.
(b) Isolated yields of 6a
With the required aldehydes 2a–c in hand, we now yields of isolated product xanthenedione 6a along with
focused on the synthesis of new xanthenedione deriva- reaction temperatures and catalysts used are shown in
tives through the condensation of aldehydes 2a–c with table 1. Among the catalysts screened, the reaction
different cyclic diketones [1,3-cyclohexanedione (3), with 20 mol% of PPA-SiO2 catalyst under solvent-free
dimedone (4) and 5-isopropyl 1,3-cyclohexanedione conditions proceeded efficiently and smoothly in
(5)] in presence of various catalysts and solvents. Ini- shorter reaction time (1.5 h) at 125◦C to give the xan-
tial efforts were focused on the reaction of aldehyde thenedione derivative 6a in very good yield in 95%
2a and 1,3-cyclohexanedione(3) with different cat- (table 1, entry 15).
alysts InCl3.3H2O,FeCl3.6H2O, LiBr, Fe2SO4.7H2O,
In order to investigate the general applicability and
SnCl2.2H2O and K5CoW12O40.3H2O CH3SO3H, p−TSA, versatility of this procedure for the synthesis of variety
montmorillonite-K10, HClO4-SiO2, H2SO4-SiO2. The of substituted xanthenedione derivatives, condensation
Scheme 2. Synthesis of tricyclic heterocycle tethered xanthenediones 6a–c, 7a–c and 8a–c.

Synthesis and absorption studies of Xanthene-1,8-diones
807
Table 2. Synthesis of novel dibenzo[b, d]furan, dibenzo[b, d]thiophene, 9-methyl-9H-
carbazole embedded xanthene-1,8-diones 6a-c, 7a-c and 8a-c with recyclable PPA-SiO2
catalyst.
S.No
Aldehyde
diketone
Product a
Reaction time (h)
Yield (%)b
1
2
3
4
5
6
7
8
9
2a
2a
2a
2b
2b
2b
2c
2c
2c
3
4
5
3
4
5
3
4
5
6a
7a
8a
6b
7b
8b
6c
7c
8c
1.5
2
1.5
1.5
1.5
2
1.5
2
2
95
92
94
91
93
92
93
91
94
a) All the reactions were performed without solvent at 125◦C.
b) Yields of isolated products.
Figure 1. Structures of xanthenedione derivatives 6, 7 and 8.
Figure 2. ORTEP diagram of compound 7a.
of aldehydes 2a, 2b and 2c with activated methylene hexane-1,3-dione (5) were examined (scheme 2). All
compounds such as cyclohexane-1,3-dione (3); 5,5- these reactions proceeded to yield the corresponding
dimethyl cyclohexane-1,3-dione (4); 5-isopropylcyclo xanthenediones 6a–c, 7a–c and 8a-c in very good yields

808
Thirumal Yempala et al.
Table 3. Comparison of absorption properties of compounds 6a–c, 7a–c and 8a–c.
λmax(nm){εmax( L mole−1 cm−1)}
S. No
Product
In CHCl3
In THF
In CH3-CN
1
2
3
4
5
6
7
8
6a
7a
8a
6b
7b
8b
6c
7c
8c
9
287.5(29373)
290.5(28880)
289.5(19660)
297.5(12824)
289.5(20296)
297.5(14221)
290.5(21491)
291(16719)
289.5(25673)
——-
288.5(36398)
289.5(29807)
289(25702)
293.5(14715)
293(25158)
293(20512)
286.5(17261)
286.5(22569)
286(23000)
302(17000)
287(17437)
288(26259)
287(20634)
292(11495)
291.5(24707)
292(8442)
285(17270)
285(13889)
286(14000)
294(5300)
9
10a
a) Product 9 refers to the xanthenedione derivative formed from benzaldehyde and dimedone.
∼90–95% (table 2). All the products (figure 1) thus be assigned due to the excitation of π electrons existing
obtained were fully characterized by IR, 1H NMR, 13
NMR and Mass spectral analysis.
C
in the xanthenedione derivatives 6a–c, 7a–c and 8a–c.
Further to study the effect of solvent on the UV-
The structure of xanthenedione 7a was confirmed Visible absorption properties of xanthenediones, inves-
from its single-crystal X-ray crystallographic analysis tigations were carried out using various solvents like
(figure 2).
tetrahydrofuran and acetonitrile and the results were
The possible application of these newly synthe- correlated with the absorption properties in chloroform
sized xanthenedione derivatives were investigated for (figure 4–6 and table 3). Among these xanthenediones
their optical behaviour due to extended conjugation evaluated, compounds having dibenzo[b, d]furan 6a, 7a
with in-built pyran ring system. The properties of the and 8a has shown greater molar extinction coefficient
newly synthesized xanthenediones 6a-c, 7a-c and 8a-c than that of the other xanthenedione derivatives 6b–c,
were investigated using JASCO UV-Visible absorption 7b-c, and 8b-c. Moreover observation of the figures 3–
spectrophotometer in dilute solutions of chloroform at a 5, revealed that the xanthenedione derivative 6a, 7a and
concentration of 10−5 moles/lit. The data obtained was 8a did not exhibit any solvatochromism. Almost all the
summarized in table 3. All the xanthenedione deriva- compounds have shown greater εmax in tetrahydrofuran
tives 6a–c, 7a–c and 8a–c exhibited similar absorp- solvent compared to other solvents used.
tion spectras with comparable molar absorptivities at an
When correlated with the known xanthenedione
absorption maxima (λmax) in the region of 287–291nm 912 having phenyl ring (i.e., xanthenedione derived
in chloroform (figure 3). This absorption bands could from benzaldehyde and dimedone, figure 7), the newly
0.35
0.30
6a
Chloroform
Acetonitrile
Tetrahydrofuran
7a
8a
6b
7b
8b
6c
7c
8c
0.30
0.25
0.20
0.15
0.10
0.05
0.00
0.25
0.20
0.15
0.10
0.05
0.00
250
300
350
400
240
250
260
270
280
290
300
310
320
330
340
Wavelength (nm)
Wavelength (nm)
Figure 3. Absorption Spectrum of 6a-c, 7a-c and 8a-c in Figure 4. Absorption Spectrum of 7a in THF, CH3-CN and
CHCl3 at a concentration of 10−5 M.
CHCl3.

Synthesis and absorption studies of Xanthene-1,8-diones
809
0.50
0.45
0.40
0.35
0.30
0.25
0.20
0.15
0.10
0.05
0.00
synthesized xanthenedione derivatives 6a–c, 7a–c and
8a–c showed higher molar extinction values (εmax) and
lower absorption wavelengths (λmax). The lowering in
the absorption wavelengths may be due to the interfer-
ence of the non-bonded electrons present on the het-
eroatom with the extending π bonded conjugated elec-
trons which results in increasing the energy gap (Eg)
between HOMO and LUMO.13
Chloroform
Acetonitrile
Tetrahydrofuran
4. Conclusions
We have described an efficient one-pot synthesis
of novel dibenzofuran, carbazole and dibenzothio-
phene embodied xanthenediones (6a–c, 7a–c and 8a–c)
through the condensation of respective aldehydes with
cyclic 1,3-diketones in the presence of PPA-SiO2 cat-
alyst (20 mol%). Absorption spectra of all the newly
synthesized xanthenediones 6a–c, 7a–c and 8a–c sug-
gested that the new compounds have greater molar
extinction coefficient values when compared to the xan-
thenedione formed from benzaldehyde and dimedone.
240
250 260
270 280
290 300
310 320
330 340
Wavelength (nm)
Figure 5. Absorption Spectrum of 7b in THF, CH3-CN
and CHCl3.
0.5
0.4
Supplementary Information
Chloroform
Acetonitrile
Tetrahydrofuran
CCDC 849770 contains Crystallographic data for the
compound 7a. This data can be obtained free of
charge via http://www.ccdc.cam.ac.uk/datarequest/cif.
0.3
0.2
0.1
0.0
1
Scanned copies of H, 13C and ESI-HRMS spectra of
6a-c, 7a-c and 8a-c are given in electronic supporting
information available at www.ias.ac.in/chemsci.
Acknowledgments
Authors (TY and SK) are thankful to Dr. Lakshmi
Kantham, Director and Dr. V. J.Rao, Head, Crop Pro-
tection Chemicals Division, IICT, Hyderabad for their
continuous support and financial assistance from CSIR
projects (NWP0054 and NWO0055). TY (SRF) is
thankful to CSIR for fellowship.
240
250 260
270 280
290 300
310 320
330 340
Wavelength (nm)
Figure 6. Absorption Spectrum of 7c in THF, CH3-CN and
CHCl3.
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