Chemical Papers 70 (12) 1658–1664 (2016)
DOI: 10.1515/chempap-2016-0098

ORIGINAL PAPER

Facile and efficient synthesis of xanthenedione derivatives promoted
by niobium pentachloride

Willian H. dos Santos, Luiz C. Da Silva-Filho*

Department of Chemistry, Faculty of Sciences, São Paulo State University (UNESP),

Av. Eng. Luiz Edmundo Carrijo Coube, 14-01, Bairro: Vargem Limpa, 17033-360, Bauru, São Paulo, Brazil

Received 5 January 2016; Revised 5 May 2016; Accepted 16 May 2016

Xanthenedione derivatives were synthesised in one-pot reactions between arylaldehyde derivatives
and 1,3-cyclohexanedione promoted by niobium pentachloride. This new method is simple, cost-
effective, high-yielding with a good variety of substrates generality, and can be conducted within
reasonable reaction times.
c© 2016 Institute of Chemistry, Slovak Academy of Sciences

Keywords: niobium pentachloride, Lewis acid, xanthenedione derivatives, one-pot reactions

Introduction

Among the various classes of natural compounds,
xanthene derivatives have received special attention
since many of these compounds have biological and
therapeutic properties (Chibale et al., 2003; El-Brashy
et al., 2004). Xanthene derivatives are recognised for
their use as sensitising dyes (Bhowmik & Ganguly,
2005), in photodynamic therapy to destroy tumour
cells (Ormond & Freeman, 2013), in laser technolo-
gies (Ahmad et al., 2002) and in pH-sensitive fluo-
rescent materials for the visualisation of biomolecules
(Knight & Stephens, 1989). Research has focused
on secondary metabolites of the genus Allanblackia
(Locksley & Murray, 1971; Nkengfack et al., 2002)
and the significant increase in the number of stud-
ies stems from the fact that many of these secondary
metabolites, such as xanthones, benzophenones and
pentacyclic triterpenes, exhibit biological, pharmaco-
logical, anti-inflammatory, antimicrobial, antifungal,
HIV-inhibitory and cytotoxic properties (Fuller et al.,
1999; Peres et al., 2000; Peres & Nagem, 1997). The
plants of the genus Allanblackia, which belong to the
family Clusiaceae, are found in large forests in the west
and south of the province of Cameroon, where they
are used to treat respiratory diseases, toothache and
diarrhoea (Fobane et al., 2014). Rhodomyrtone A (I)

and rhodomyrtosone I (II ) extracted from Rhodomyr-
tus tomentosa (Hiranrat et al., 2012; Hiranrat & Ma-
habusarakam, 2008; Limsuwan et al., 2009; Sianglum
et al., 2011; Visutthi et al., 2011), together with the
compound known as BF-6 (III ) extracted from the
leaves of Baeckea frutescens (Makino & Fujimoto,
1999) are examples of natural xanthenediones (Fig. 1).
Xanthene derivatives can be prepared by several

methods: cyclodehydration (Bekaert et al., 1992), the
trapping of benzynes by phenols (Knight & Little,
2001), the palladium-catalysed cyclisation of poly-
cyclic aryltriflate esters (Wang & Harvey, 2002),
a simple and efficient procedure for the synthesis
of xanthene derivatives through one-pot condensa-
tion of 2-naphthol with aryl aldehydes in the pres-
ence of niobium pentachloride (Bartolomeu et al.,
2014), the condensation of cyclohexane-1,3-diones and
aromatic aldehydes in the presence of solid acids
Y(NO3)3 · 6H2O and SnCl2 ·2H2O (Karami et al.,
2013a), amongst others (Horning & Horning, 1946;
John et al., 2006; Saini et al., 2006; Zhang & Tao 2008;
Zhang & Liu, 2008; Wang et al., 2008; Urinda et al.,
2009; Lü et al., 2009; Maleki et al., 2011; Soleimani
et al., 2011; Pramanik & Bhar, 2012; Dharma Rao et
al., 2012; Karami et al., 2013b, 2013a, 2014; Li et al.,
2013; Cao et al., 2013; Shirini et al., 2013; Napoleon
& Khan 2014; Napoleon et al., 2014; Iniyavan et al.,

*Corresponding author, e-mail: lcsilva@fc.unesp.br



W. H. dos Santos, L. C. Da Silva-Filho/Chemical Papers 70 (12) 1658–1664 (2016) 1659

Fig. 1. Examples of natural xanthenediones.

Fig. 2. Synthesis of xanthenedione derivatives.

2014; Shirini et al., 2014, 2015; Preetam et al., 2015;
Ilangovan et al., 2011). However, some of these meth-
ods involve long reaction times, extreme reaction con-
ditions, expensive reagents and unsatisfactory yields,
hence the improvement of these syntheses has been the
target of several studies. One-pot reactions are effec-
tive for carrying out numerous transformations and
forming several bonds in a single pot while, at the
same time, eliminating several purification steps, min-
imising chemical waste generation and saving time.
Such advantages have significant relevance in mod-
ern synthetic methodology (D’Souza & Müller, 2007;
Isambert & Lavilla, 2008).
As part of the present investigation of the use of

NbCl5 as a promoter in organic reactions, this work
describes a new route for the preparation of xan-
thenedione derivatives (VIa–VIn) through a one-pot
reaction between aldehyde derivatives (Va–Vn) and
1,3-cyclohexanedione (IV) promoted by niobium pen-
tachloride (Fig. 2).
Niobium pentachloride is a stronger Lewis acid cur-

rently attracting interest as a reagent in organic syn-
thesis; it has found applications as an effective catalyst
in a variety of organic reactions (Andrade, 2004; Guo
et al., 2011; Hou et al., 2010b, 2010a, 2011a, 2011b;
Lacerda et al., 2012; Oshiro et al., 2015; Bartolomeu
et al., 2014, 2015).

Experimental

The solvents were distilled with CaH2. All chemi-
cals were purchased from Sigma–Aldrich (USA) and
used without further purification, with the excep-
tion of NbCl5. The NbCl5 used was supplied by

Companhia Brasileira de Metalurgia e Mineração
(CBMM, Brasil) and re-crystallised by sublimation
following the procedure detailed in the supplemen-
tary data; this method is described in the litera-
ture (Alves, 1986). Thin-layer chromatography was
performed on 0.2 mm Merck 60F254 silica gel alu-
minium sheets (Germany), with visualisation using a
vanillin/methanol/water/sulphuric acid mixture. In-
frared (IR) spectra were recorded using a Bruker Ver-
tex 70 Fourier Transform Spectrometer (Germany)
equipped with a Bruker Platinum ATR unit (Ger-
many). A Bruker DRX 400 spectrometer was em-
ployed for generating the NMR spectra (CDCl3 as
a solvent) using tetramethylsilane as internal refer-
ence. HR-MS analyses were performed on an LCMS-
IT-TOF mass spectrometer (Shimadzu, Japan). The
melting points of the synthesised compounds were de-
termined by differential scanning calorimetry (DSC).
DSC measurements were performed using a Mettler-
Toledo model DSC 1 stare system.

General procedure for syntheses of xanthene-
dione derivatives (VIa–VIm)

To a solution of NbCl5 (67.5 mg, 0.25 mmol) in an-
hydrous CH3CN (2.0 mL), maintained under N2 atmo-
sphere (Table 1), a solution of 1,3-cyclohexanedione
(IV; 224 mg, 2.0 mmol) and the respective ary-
laldehyde (Va–Vn; 1.0 mmol) in anhydrous CH3CN
(3.0 mL) were added. The reaction mixture was stirred
under reflux for 2 h. Next, the reaction mixture was
poured into water (10.0 mL) at 0◦C and the precip-
itate was filtered and washed with a mixture of ace-
tone/water (ϕr = 1 : 1). The products were dissolved



1660 W. H. dos Santos, L. C. Da Silva-Filho/Chemical Papers 70 (12) 1658–1664 (2016)

Table 1. Optimisation of one-pot reaction between IV and Va promoted by NbCla,b5

Entry NbCl5 (mole %) Solvent Time (h) Yieldc (%)

1a 0 DCM 24 –
2a 10 DCM 2 15
3a 25 DCM 2 22
4a 50 DCM 2 19
5a 0 DCE 24 –
6a 10 DCE 2 18
7a 25 DCE 2 45
8a 50 DCE 2 33
9a 0 CH3CN 24 –
10a 25 CH3CN 2 90
11a 50 CH3CN 2 77
12b 10 CH3CN 2 25
13b 25 CH3CN 2 87
14b 50 CH3CN 2 75

a) Reaction conditions: 1,3-cyclohexanedione (IV) (2.0 mmol), benzaldehyde (Va) (1.0 mmol) and NbCl5 (0–50 mole %) in
dichloromethane (DCM; 3.0 mL), 1,2-dichloroethane (DCE; 3.0 mL) or CH3CN (3.0 mL) under reflux, in an N2 atmosphere;
b) reaction conditions: IV (2.0 mmol), Va (1.0 mmol) and NbCl5 (25–50 mole %) in CH3CN (3.0 mL) under reflux, in an N2
atmosphere; c) isolated yields by re-crystallisation.

Table 2. Results for synthesis of xanthenedione derivatives (VIa–VIn)

M.p/◦C
Compound R Appearence Yield (%)a ΔHfusion (J g−1) Purity (%)

Found Reportedb

Va C6H5 white solid 87 (VIa) –135.86 99 263.9 261–264 (Shirini et al., 2013)
Vb 4-CH3C6H4 white solid 77 (VIb) –127.38 98 253.1 249–251 (Shirini et al., 2013)
Vc 4-COOHC6H4 white solid 66 (VIc)c –75.79 99 281.8 –
Vd 4-OCH3C6H4 white solid 73 (VId) –103.81 99 193.4 203–204 (Shirini et al., 2013)
Ve 2-OCH3C6H4 white solid 65 (VIe) –74.24 96 212.2 216–218 (Maleki et al., 2012)
Vf 4-OH-3-OCH3C6H3 white solid 80 (VIf) –118.16 98 239.0 225–227 (John et al., 2006)
Vg 3-NO2C6H4 white solid 57 (VIg) –89.98 99 281.2 281–283 (Shirini et al., 2013)
Vh 4-NO2C6H4 white solid 61 (VIh) –82.34 98 255.3 248–250 (Shirini et al., 2013)
Vi 4-BrC6H4 white solid 64 (VIi) –73.43 99 251.1 283–285 (Shirini et al., 2013)
Vj 2-BrC6H4 white solid 55 (VIj) –65.57 97 250.0 255–256 (Li et al., 2013)
Vk 4-C6H5C6H4 white solid 70 (VIk) –84.72 98 211.6 196–198 (Iniyavan et al., 2015)
Vl C4H3S white solid 69 (VIl)c –71.01 98 210.1 –
Vm 4-(CH3)2NC6H4 white solid 54 (VIm) –77.81 98 233.2 218–220 (Napoleon et al., 2014)
Vn 4-COH-C6H4 white solid 78 (VIn) – – > 325.0 > 300.00 (Kaya et al., 2011)

a) Yields of isolated products by re-crystallisation; b) products known in the literature and their melting points were compared
with values already reported; c) product not described in the literature.

in 10.0 mL of hot ethanol, and cooled in a freezer to
afford the compounds (VIa–VIn). The full experimen-
tal details and spectroscopic characterisations (1H and
13C NMR, DSC, infrared and mass spectrometry) for
compounds (VIa–VIm) can be found in the Supple-
mentary Data section of this article’s web page.

Results and discussion

First, the one-pot reaction between IV (2.0 mmol)
and benzaldehyde (Va; 1.0 mmol), in the presence
of different concentrations (0 mole %, 10 mole %,
25 mole % or 50 mole %) of niobium pentachloride
and different types of anhydrous solvents (acetonitrile,
dichloromethane and 1,2-dichloroethane), was used as
a model in order to develop a protocol for optimising

the reaction conditions. The reaction was conducted
by heating under reflux, in an N2 atmosphere (Table 1,
entries 1–11) or in an air atmosphere (Table 1, entries
12–14). The results are summarised in Table 1.
The results in Table 1 show that the reactions with

0 mole % and 10 mole % of NbCl5 lead to no or in-
significant yields, independent of the solvent used. The
use of 25 mole % of NbCl5 afforded the best yields
in the three solvents tested, of which the acetonitrile
showed the best yields (87 % in 2 h) (Table 1, entry
13). With 50 mole % of NbCl5, the product started to
degrade and other products were formed, resulting in
a reduction in yield (Table 1, entries 11 and 14). From
these results, a time of 2 h, 25 mole % of NbCl5 and
air atmosphere (Table 1, entry 13) were established
as optimal for the other reactions performed.



W. H. dos Santos, L. C. Da Silva-Filho/Chemical Papers 70 (12) 1658–1664 (2016) 1661

Table 3. Spectral data of compounds (VIa–VIm)

Compound Spectral data

VIa IR, ν̃/cm−1: 2948, 2889, 1650, 1618, 1494, 1450, 1421, 1359, 1200, 1172, 1130, 1012, 958
1H NMR (CDCl3, 400 MHz), δ: 7.33–7.29 (m, 2H), 7.23 (dd, J = 6.9 Hz (2×), 2H), 7.13 (m, 1H), 4.83 (s, 1H),
2.70–2.52 (m, 4H), 2.41–2.30 (m, 4H), 2.08–1.96 (m, 4H)
13C NMR (CDCl3, 100 MHz), δ: 196.5, 163.9, 144.3, 128.4, 128.1, 126.4, 116.9, 36.9, 31.6, 27.1, 20.3
HRMS (ESI), m/z: Calcd. for C19H18O3 [M + Na]+: 317.1148, found 317.1129

VIb IR, ν̃/cm−1: 3030, 2952, 2892, 1650, 1614, 1510, 1452, 1417, 1355, 1338, 1232, 1197, 1172, 1012, 954
1H NMR (CDCl3, 400 MHz), δ: 7.19 (d, J = 8.1 Hz, 2H), 7.04 (d, J = 8.1 Hz, 2H), 4.78 (s, 1H), 2.68–2.52 (m, 4H),
2.41–2.30 (m, 4H), 2.29–2.25 (m, 4H)
13C NMR (CDCl3, 100 MHz), δ: 196.6, 163.8, 141.5, 135.9, 128.8, 128.2, 117.0, 37.0, 31.2, 27.1, 21.1, 20.3
HRMS (ESI), m/z: Calcd. for C20H20O3 [M + Na]+: 331.1305, found 331.1308

VIc IR, ν̃/cm−1: 3531, 2948, 2887, 1720, 1670, 1650, 1604, 1427, 1361, 1272, 1203, 1174, 1130, 1110, 1014, 958
1H NMR (CDCl3, 400 MHz), δ: 7.55 (d, J = 8.3 Hz, 2H), 7.01 (d, J = 8.3 Hz, 2H), 4.45 (s, 1H), 2.39-2.27 (m, 4H),
2.04-1.97 (m, 4H), 1.77-1.64 (m, 4H)
13C NMR (CDCl3, 100 MHz), δ: 196.4, 168.0, 164.5, 149.3, 129.4, 128.9, 128.3, 115.9, 36.8, 31.7, 26.9, 20.1
HRMS (ESI), m/z: Calcd. for C20H18O5 [M + Na]+: 361.1046, found 361.1032

VId IR, ν̃/cm−1: 2956, 2889, 2838, 1650, 1616, 1510, 1459, 1440, 1427, 1378, 1357, 1334, 1257, 1234, 1201, 1168, 1132,
1029, 956
1H NMR (CDCl3, 400 MHz), δ: 7.22 (d, J = 8.8 Hz, 2H), 6.77 (d, J = 8.8 Hz, 2H), 4.77 (s, 1H), 3.74 (s, 3H),
2.68–2.53 (m, 4H), 2.42–2.29 (m, 4H), 1.95–2.09 (m, 4H)
13C NMR (CDCl3, 100 MHz), δ: 196.6, 163.7, 158.0, 136.7, 129.3, 117.1, 113.5, 55.1, 36.9, 30.8, 27.1, 20.3
HRMS (ESI), m/z: Calcd. for C20H20O4 [M + Na]+: 347.1254, found 347.1252

VIe IR, ν̃/cm−1: 2943, 2873, 2831, 1650, 1620, 1488, 1467, 1454, 1429, 1382, 1357, 1334, 1290, 1245, 1207, 1176, 1134,
1116, 1045, 1027, 958
1H NMR (CDCl3, 400 MHz), δ: 7.39 (dd, J = 7.6 Hz, 1.8 Hz, 1H), 7.19–7.04 (m, 1H), 6.88 (ddd, J = 7.5 Hz, 7.5 Hz,
1.0 Hz, 1H), 6.80 (d, J = 8.3 Hz, 1H), 4.91 (s, 1H), 3.81 (s, 3H), 2.65–2.47 (m, 4H), 2.36–2.25 (m, 4H), 2.05–1.91
(m, 4H)
13C NMR (CDCl3, 100 MHz), δ: 196.7, 164.3, 158.0, 131.9, 131.5, 127.8, 120.5, 115.3,111.6 55.7, 37.0, 29.2, 27.1,
20.4
HRMS (ESI), m/z: Calcd. for C20H20O4 [M + Na]+: 347.1254, found 347.1242

VIf IR, ν̃/cm−1: 3313, 2950, 2925, 1662, 1641, 1618, 1510, 1467, 1454, 1434, 1380, 1359, 1272, 1230, 1203, 1170, 1151,
1118, 1039, 1012, 956
1H NMR (CDCl3, 400 MHz), δ: 7.08 (d, J = 2.0 Hz, 1H), 6.75 (d, J = 8.1, Hz, 1H), 6.55 (dd, J = 8.1 Hz, 2.0 Hz,
1H), 5.49 (s, 1H), 4.74 (s, 1H), 3.92 (s, 3H), 2.68–2.53 (m, 4H), 2.44–2.31 (m, 4H), 2.07–1.95 (m, 4H)
13C NMR (CDCl3, 100 MHz), δ: 196.8, 163.8, 145.9, 144.1, 136.6, 119.7, 117.0, 113.9, 112.4, 55.9, 37.0, 31.0, 27.1,
20.2
HRMS (ESI), m/z: Calcd. for C20H20O5 [M + Na]+: 363.1203, found 363.1202

VIg IR, ν̃/cm−1: 2954, 2890, 2823, 1650, 1620, 1521, 1415, 1384, 1348, 1253, 1234, 1201, 1170, 1130, 1080, 1014, 958
1H NMR (CDCl3, 400 MHz), δ: 8.06–7.96 (m, 2H), 7.84 (ddd, J = 7.8 Hz, 1.3 Hz (2×) Hz, 1H), 7.44–7.38 (m, 1H),
4.89 (s, 1H), 2.76–2.56 (m, 4H), 2.42–2.29 (m, 4H), 2.12–1.94 (m, 4H)
13C NMR (CDCl3, 100 MHz), δ: 196.6, 164.6, 148.3, 146.4, 135.9, 128.7, 122.6, 121.7, 115.7, 36.8, 31.9, 27.1, 20.2
HRMS (ESI), m/z: Calcd. for C19H17NO5 [M + Na]+: 362.0999, found 362.0988

VIh IR, ν̃/cm−1: 2946, 2925, 2871, 1656, 1606, 1593, 1517, 1458, 1425, 1384, 1346, 1247, 1232, 1199, 1170, 1126, 1058,
1012, 956
1H NMR (CDCl3, 400 MHz), δ: 8.10 (d, J = 8.8 Hz, 2H), 7.48 (d, J = 8.8 Hz, 2H), 4.88 (s, 1H), 2.70–2.59 (m, 4H),
2.39–2.30 (m, 4H), 2.02–1.96 (m, 4H)
13C NMR (CDCl3, 100 MHz), δ: 196.4, 164.5, 151.6, 141.4, 133.6, 129.4, 128.0, 126.9, 123.4, 115.8, 36.8, 32.2, 27.1,
20.2
HRMS (ESI), m/z: Calcd. for C19H17NO5 [M + H]+: 340.1179, found 340.1188

VIi IR, ν̃/cm−1: 2987, 2900, 1656, 1616, 1486, 1458, 1417, 1405, 1382, 1357, 1230, 1201, 1168, 1126, 1070, 1088, 958
1H NMR (CDCl3, 400 MHz), δ: 7.34 (d, J = 8.3 Hz, 2H), 7.18 (d, J = 8.3 Hz, 2H), 4.76 (s, 1H), 2.67–2.51 (m, 4H),
2.41–2.30 (m, 4H), 2.09–1.93 (m, 4H)
13C NMR (CDCl3, 100 MHz), δ: 196.5, 164.0, 143.4, 131.2, 130.2, 120.3, 116.4, 36.8, 31.4, 27.1, 20.3
HRMS (ESI), m/z: Calcd. for C19H17BrO3 [M + H]+: 373.0434, found 373.0454

VIj IR, ν̃/cm−1: 2985, 2950, 2877, 1660, 1620, 1467, 1429, 1378, 1357, 1336, 1234, 1199, 1176, 1130, 1010, 958
1H NMR (CDCl3, 400 MHz), δ: 7.46–7.41 (m, 2H), 7.24–7.18 (m, 1H), 7.02–6.96 (m, 1H), 5.02 (s, 1H), 2.66–2.54
(m, 4H), 2.37–2.30 (m, 4H), 2.04–1.99 (m, 4H)
13C NMR (CDCl3, 100 MHz), δ: 196.6, 164.4, 141.4, 133.5, 128.0, 126.9, 115.0, 36.9, 34.0, 27.1, 20.2, 0.0
HRMS (ESI), m/z: Calcd. for C19H17BrO3 [M + H]+: 373.0434, found 373.0461

VIk IR, ν̃/cm−1: 2983, 2906, 1660, 1618, 1483, 1450, 1432, 1380, 1357, 1228, 1201, 1174, 1126, 1088, 956
1H NMR (CDCl3, 400 MHz), δ: 7.57–7.51 (m, 2H), 7.49–7.36 (m, 6H), 7.34–7.28 (m, 1H), 4.87 (s, 1H), 2.75–2.49
(m, 4H), 2.47–2.32 (m, 4H), 2.14–1.96 (m, 4H)
13C NMR (CDCl3, 100 MHz), δ: 196.6, 163.9, 143.4, 141.2, 139.3, 128.8, 128.6, 127.0, 126.9, 116.8, 36.9, 31.3, 27.2,
20.3
HRMS (ESI), m/z: Calcd. for C25H22O3 [M + H]+: 371.1642, found 371.1654



1662 W. H. dos Santos, L. C. Da Silva-Filho/Chemical Papers 70 (12) 1658–1664 (2016)

Table 3. (continued)

Compound Spectral data

VIl IR, ν̃/cm−1: 3301, 2948, 2885, 1650, 1616, 1450, 1421, 1382, 1350, 1315, 1284, 1205, 1172, 1132, 1012, 958
1H NMR (CDCl3, 400 MHz), δ: 7.05 (dd, J = 5.1 Hz, 1.3 Hz, 1H), 6.93 (dd, J = 3.5 Hz, 0.5 Hz, 1H), 6.84 (dd, J =
5.1 Hz, 3.5 Hz, 1H), 5.19 (s, 1H), 2.72–2.60 (m, 4H), 2.54–2.41 (m, 4H), 2.10–2.01 (m, 4H)
13C NMR (CDCl3, 100 MHz), δ: 196.4, 164.2, 148.4, 126.8, 125.0, 123.5, 116.4, 36.9, 27.1, 26.1, 20.6
HRMS (ESI), m/z: Calcd. for C17H16O3S [M + Na]+: 323.0712, found 323.0706

VIm IR, ν̃/cm−1: 2941, 2889, 2804, 1718, 1689, 1656, 1612, 1521, 1456, 1452, 1386, 1357, 1226, 1174, 1124, 1066, 1010,
954.
1H NMR (CDCl3, 400 MHz), δ: 7.19–7.13 (m, 2H), 6.63–6.59 (m, 2H), 4.72 (s, 1H), 2.87 (s, 6H), 2.67–2.55 (m, 4H),
2.38–2.31 (m, 4H), 2.04–1.95 (m, 4H)
13C NMR (CDCl3, 100 MHz), δ: 196.7, 163.5, 149.2, 132.7, 130.4, 129.3, 128.9, 117.3, 112.4, 112.2, 111.6, 40.6, 40.4,
37.0, 27.2, 20.3
HRMS (ESI), m/z: Calcd. for C21H23NO3 [M + H]+: 338.1751, found 338.1747

VIn IR, ν̃/cm−1: 2948, 1669, 1619, 1504, 1453, 1359, 1233, 1175, 1130, 958, 809, 615.
1H NMR (CDCl3, 400 MHz), δ: 7.08 (s, 4H), 4.73 (s, 2H), 2.67–2.50 (m, 8H), 2.41–2.26 (m, 8H), 2.04–1.98 (m, 8H)
13C NMR (CDCl3, 100 MHz), δ: 196.7, 164.0, 141.9, 128.0, 117.0, 36.9, 30.8, 27.1, 20.1

After optimisation of the reaction conditions, other
arylaldehydes (Vb–Vn) were allowed to react in the
presence of 25 mole % of NbCl5 and anhydrous
CH3CN. The products obtained were purified by re-
crystallisation in ethanol and characterised by spec-
troscopic and spectrometric methods (1H-NMR, 13C-
NMR, IR and MS). The spectral data were compared
with those in the literature (John et al., 2006; Li et al.,
2013; Iniyavan et al., 2015; Shirini et al., 2015, 2014,
2013; Pramanik & Bhar, 2012; Napoleon & Khan,
2014; Maleki et al., 2012). The results are summarised
in Tables 2 and 3.
The results in Table 2 show that, by using 25

mole % equivalent of NbCl5 and a reaction time of
2 h, it was possible to obtain xanthenedione deriva-
tives (VIa–VIn) with good yields (55–87 %). Large
yield differences were not observed by changing the
benzaldehyde derivative and the compound (VIc) is
not described in the literature. Through differential
scanning calorimetric analysis (DSC), it was possible
to determine the melting points, purity and enthalpy
of fusion of the synthesised compounds, in accordance
with the ASTM method (ASTM, 2014). The method
employed for re-crystallisation afforded the products
of high purity (above 97 %, with the exception of com-
pound VIc).
To promote a scale-up in the process of synthesis-

ing xanthenedione derivatives, two reactions were also
effected using 10.0 mmol of arylaldehyde (Va or Vc)
in the presence of 2.5 mmol of NbCl5. The yields ob-
tained were similar to the experiments performed with
(1.0 mmol), 85 % for product VIa and 67 % for prod-
uct VIc, after re-crystallisation. These results showed
that niobium pentachloride is an excellent catalyst
for the scale-up process and large-scale applications
of these xanthenedione derivatives.
In summary, a simple and efficient procedure

for the synthesis of xanthenedione derivatives is
described. The reactions were carried out using

25 mole % of NbCl5 and acetonitrile as a solvent under
reflux, in an air atmosphere, for 2 h, affording good
yields of the products.

Conclusions

A simple and efficient procedure was developed
for preparing a variety of 9-aryl-3,4,5,6,7,9-hexahydro-
1H-xanthene-1,8(2H)-dione derivatives by the reac-
tions of various arylaldehydes with 1,3-cyclohexane-
dione in the presence of niobium pentachloride and
anhydrous acetonitrile as solvent under reflux, in an
air atmosphere, for 2 hours, affording good yields of
the products.

Acknowledgements. The authors would like to thank Fun-
dação de Amparo à Pesquisa do Estado de São Paulo
(FAPESP), Conselho Nacional de Desenvolvimento Cientí-
fico e Tecnológico (CNPq), Coordenadoria de Aperfeiçoamento
de Pessoal do Nível Superior (CAPES), and Pró-Reitoria de
Pesquisa da UNESP (PROPe-UNESP) for their financial sup-
port. The authors would also like to thank CBMM – Companhia
Brasileira de Metalurgia e Mineração for the NbCl5 samples.
The authors would also like to express their special thanks to
N. B. Dias and M. S. Palma from the São Paulo State Univer-
sity in Rio Claro for their HR-MS analyses, and to Bannach,
G., Guerra, R. B., Ferreira, L. T. and Alarcon, R. T. for their
DSC analyses.

Supplementary data

Supplementary data associated with this article
can be found in the online version of this paper (DOI:
10.1515/chempap-2016-0098).

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