A novel procedure for the synthesis of 14-aryl-14Hdibenzo[a,j]xanthenes through one-pot condensation of b-naphthol with aryl halides in aqueous media catalyzed by bis-piperidinium compounds is described. The method resulted in good to excellent yields in short reaction times

Ahmad, Matloob

Ali Shahid Chatha, Shehzad

Jawwad Saif, Muhammad

Mansha, Asim

Revistes Catalanes amb Accés Obert

AfinidAd LXX, 562, Abril-Junio 2013 139
RESUMEN
Se describe un nuevo procedimiento para la síntesis de 
14-aril-14H-dibenzo [a,j]xantenos a través de una conden-
sación en recipiente único de β-naftol con haluros de arilo 
en medio acuoso, catalizada por derivados de bis-piperi-
dinio. El método dio como resultado rendimientos entre 
buenos y excelentes en tiempo de reacción cortos.
Palabras clave: dibenzoxantenos, derivados de bis-pipe-
ridinio
SUMMARY
A novel procedure for the synthesis of 14-aryl-14H-
dibenzo[a,j]xanthenes through one-pot condensation of 
β-naphthol with aryl halides in aqueous media catalyzed 
by bis-piperidinium compounds is described. The method 
resulted in good to excellent yields in short reaction times.
Keywords: dibenzoxanthenes, bis-piperidinium com-
pounds
RESUM
Es descriu un nou procediment per a la síntesi de 
14-aril-14H-dibenzo [a,j]xantens a través d’una condensa-
ció en recipient únic, de β-naftol amb halurs d’aril en medi 
aquós, catalitzada per derivats de bis-piperidini. El mèto-
de va donar com a resultat uns rendiments entre bons i 
excel·lents en temps de reacció curts.
Paraules clau: dibenzoxantens, derivats de bis-piperidini
INTRODUCTION
The synthesis of xanthenes, especially benzoxanthenes 
(Fig 1), has attracted the interest of chemists due to its 
diverse biological and pharmaceutical properties like 
antiplasmodial [1], antiviral [2] and anti-inflammatory ac-
tivities [3]. Besides, the heterocyclic compounds have 
been utilized as sensitizers in photodynamic therapy [4], 
as dyes [5], and in laser technology [6]. This importance 
of benzoxanthenes has instigated various researchers to 
investigate its synthetic methodology. Various methods 
have been reported in literature to build the benzoxan-
thenes scaffold, such as the reaction of 2-naphthol with 
aldehyde acetals [7], carbon monoxide [8], cycloconden-
sation of 2-hydroxyaromatic aldehydes with 2-tetralone 
[9], trapping of benzynes by phenols [10] and palladium 
catalysed cyclization of polycyclic aryltriflate esters [11]. 
An improvement in reaction procedure is made by react-
ing 2-naphthol with alkyl/aryl aldehydes employing vari-
ous catalysts such as p-toluenesulfonic acid [12], sulfa-
mic acid [13], ionic liquids [14], bismuth(III) chloride [15], 
mesoporous zirconium phosphate [16], methanesulfonic 
acid [17] and amberlyst-15 [18]. However, these methods 
suffer from certain limitations such as long reaction times, 
tedious experimental protocols, poor yields, and necessity 
to use reagents in excess. Thus, there is a need to develop 
a milder and cleaner procedure for the synthesis of ben-
zoxanthenes. As part of our research program directed to-
wards the development of highly expedient methods and 
development of diverse heterocycles, we herein report a 
Efficient, one-pot synthesis of 14-aryl-14H-
dibenzo[a, j]xanthenes in aqueous medium 
catalyzed by bis-piperidinium compounds
Muhammad Jawwad Saif*, Shehzad Ali Shahid Chatha, Matloob Ahmad and Asim Mansha
Institute of Chemistry, Government College University Faisalabad  - Pakistan
Una síntesis eficiente, en recipiente único, de 14-aril-14H-dibenzo[a, j]
xantenos en medio acuoso catalizada por derivados de bis-piperidinio
 
Una síntesi eficient, en recipient únic, de 14-aril-14H-dibenzo[a, j]xantens 
en medi aquós catalitzada per derivats de bis-piperidini
Recibido: 22 de octubre de 2012; aceptado: 11 de febrero de 2013
*Corresponding author: jawwadsaif@gmail.com
AfinidAd LXX, 562, Abril-Junio 2013140
new and convenient practical method for the synthesis of 
14-aryl- or alkyl-14H-dibenzo[a,j]xanthenes from the reac-
tion of aldehydes and 2-naphthol catalysed by employ-
ing bis-piperidinium compounds as catalyst in aqueous 
medium. To the best of our knowledge in the literature, 
bis-piperidinium compounds have not been employed as 
catalysts for the synthesis of benzoxanthenes.
O
7
14
8
95
6
10
11
12
131
2
3
4
HR
Fig 1. Benzoxanthenes
RESULTS AND DISCUSSION
We have already reported the synthesis and catalytic 
activity of some bis-piperidinium compounds in N-alkyl-
ation and O-alkylation reactions [19]. The preparation of 
bis-piperidinium compounds (1a-1b) was performed by 
amination of p-xylylene dibromide with two equivalents of 
piperidine followed by quaternization with alkyl halides to 
obtain the bis-quaternary compounds in almost quantita-
tive yields. (Scheme 1)
piperidinium compounds have not been employed as catalysts for the synthesis of 
benzoxanthenes. 
 
 
 
Fig 1. Benzoxanthenes 
Results and Discussion    
 
We have already reported the synthesis a d catalytic activity of some bis-piperidinium 
compounds in N-alkylation and O-alkylation reactions [19]. The preparation of bis-piperidinium 
compounds (1a-1b) was performed by amination of p-xylylene dibromide with two equivalents 
of piperidine followed by quaternization with alkyl h ides to obtain the bis-quaternary 
compounds in almost quantitative yields. (Scheme 1) 
 
    
R = -ethyl (1a), butyl (1b) 
Scheme 1. 
 
In an initial experiment, we tried the condensation of -naphthol and 4-bromobenzaldehyde (2:1) 
using catalysts 1a and 1b separately, by refluxing in dichloromethane for 3 hours. The catalysts, 
1a & 1b afforded dibenzo[a,j]xanthene in high yields (91%, 95% respectively). A control 
reaction was carried out in the absence of the catalysts under similar experimental conditions. It 
was observed that there is no conversion of the starting material into the desired product even 
after 12 hours. 
N
N
R
R
X-
X-
Br
Br
N
+
H
N
N
K2CO3
acetonitrile
2R-X
R = -ethyl (1a), butyl (1b)
Scheme 1.
In an initial experiment, we tried the condensation of β-
naphthol and 4-bromobenzaldehyde (2:1) using catalysts 
1a and 1b separately, by refluxing in dichloromethane for 
3 hours. The catalysts, 1a & 1b afforded dibenzo[a,j]xan-
thene in high yields (91%, 95% respectively). A control 
reaction was carried out in the absence of the catalysts 
under similar experimental conditions. It was observed 
that there is no conversion of the starting material into the 
desired product even after 12 hours.
Aqueous mediated reactions are becoming more popular 
in organic synthesis due to environment friendly protocols. 
Same experiment was performed in aqueous medium 
while heating the reaction mixture at 100OC for 3 hours 
(sufficient time for the completion of reaction as indicated 
by TLC). For the both the catalysts, 1a & 1b, dibenzo[a,j]
xanthene was obtained in 90% and 93%, respectively. 
(Scheme 2)
Aqueous mediated reactions are becoming more popular in organic synthesis due to environment 
friendly protocols. Same experiment was performed in aqueous medium while heating the 
reaction mixture at 100OC for 3 hours (sufficient time for the completion of reaction as indicated 
by TLC). For the both the catalysts, 1a & 1b, dibenzo[a,j]xanthene was obtained in 90% and 
93%, respectively. (Scheme 2) 
 
 
Scheme 2. 
 
In order to optimize the catalyst loading, condensation of -naphthol and 4-bromobenzaldehyde 
(2:1) was carried out using 5 mol%, 10 mol% and 15 mol% catalyst loading while keeping the 
other experimental protocols unvaried. A catalyst loading of 15 mol% was found to be 
appropriate to obtain dibenzo[a,j]xanthene in maximum yield in low time.  
Experiments were extended with various aliphatic and aromatic aldehydes to prepare a series of 
dibenzo[a,j]xanthene and to fully evaluate the potential of bis-piperidinium compounds (1a & 
1b) as catalyst for such transformations. Good to excellent yields were obtained in all cases. As 
expected, in case of aromatic aldehydes possessing electron withdrawing groups, the reaction 
appeared to be completed in shorter time as compared to those having electron donating groups. 
In case of ortho-substituted aldehydes, yields were little lower as compared to meta- or pera- 
analogues because of steric factors. Results are summarized in Table 1 which show that both the 
bis-piperidinium compounds possess excellent catalytic activity for the preparation of 
dibenzo[a,j]xanthene from the condensation of -naphthol and alkyl/aryl aldehydes. 
 
Table 1. Condensation of -naphthol and aldehydes
 
Entry R Product Catalyst 1a 
(Yield %)
Catalyst 2a 
(Yield %)
Mp (oC)/(lit.) 
1 4-Br.C6H4 4a 90 93 295 (296) [20] 
2 C6H5 4b 88 89 181 (181-183) [21] 
3 4-CH3.C6H4 4c 89 91 227 (228-229) [17] 
4 4-OCH3.C6H4 4d 91 92 202 (202-203) [17] 
5 2-NO2.C6H4 4e 82 81 214 (213-214) [21] 
6 3-NO2.C6H4 4f 87 89 209-211 (211-212) [17] 
7 4-NO2.C6H4 4g 98 97 310-311 (311-312) [21] 
8 4-Cl.C6H4 4h 88 90 287-288 (288-289) [17] 
9 2- Cl.C6H4 4i 81 84 214-215 (215-216) [17] 
Scheme 2.
In order to optimize the catalyst loading, condensation of 
β-naphthol and 4-bromobenzaldehyde (2:1) was carried 
out using 5 mol%, 10 mol% and 15 mol% catalyst loading 
while keeping the other experimental protocols unvaried. 
A catalyst loading of 15 mol% was found to be appropri-
ate to obtain dibenzo[a,j]xanthene in maximum yield in low 
time. 
Experiments were extended with various aliphatic and 
aromatic aldehydes to prepare a series of dibenzo[a,j]xan-
thene and to fully evaluate the potential of bis-piperidinium 
compounds (1a & 1b) as catalyst for such transformations. 
Good to excellent yields were obtained in all cases. As ex-
pected, in case of aromatic aldehydes possessing electron 
withdrawing groups, the reaction appeared to be complet-
ed in shorter time as compared to those having electron 
donating groups. In case of ortho-substituted aldehydes, 
yields were li tle lower as compared to meta- or pera- ana-
logues because of steric factors. Results are summarized 
in Table 1 which show that both the bis-piperidinium com-
pounds possess excellent catalytic activity for the prepa-
ration of dibenzo[a,j]xanthene from the condensation of 
β-naphthol and alkyl/aryl aldehydes.
EXPERIMENTAL
General Procedure for the Preparation of bis-piperidinium 
compounds 1a-1b
Bis-piperidinium compounds were prepared according to 
over previously reported procedure  and were employed 
without further modifications [19]. Piperidine was first re-
acted with 1,4-Bis(bromomethyl)benzene and further qua-
ternized with 1-bromoethane or 1-bromobutane to obtain 
compound 1a or 1b, respectively.
General Procedure for the synthesis of alkyl- or aryl-14H-
dibenzo[a,j]xanthenes.
A mixture of aldehyde (1mmol), β-naphthol (2 mmol) and 
bispiperidinium catalyst - 1a or 1b (15 mol%) in water (10 
mL) was heated at 100oC with stirring for 3 hours. After 
completion of reaction as confirmed by TLC, reaction mix-
ture was cooled to room temperature. The crude prod-
uct was filtered and recrystallized from ethanol. All of the 
synthesized compounds were characterized by m.p. and 
1H NMR analysis. Spectroscopic data for some selected 
compou s is given below:
14-(4-bromophenyl)-14H-dibenzo[a,j]xanthene 4a
mp 295oC. 1H NMR (400 MHz, CDCl3): d = 8.30 (d, 2H, 
J = 8.39 Hz), 7.83-7.75 (m, 4H), 7.58-7.52 (m, 2H), 7.46-
7.38 (m, 5H), 7.25-7.21 (m, 3H), 6.48 (s, 1H); 13C NMR (100 
MHz, CDCl3): d = 149.1, 145.3, 132.8, 131.2, 130.8, 130.5, 
130.1, 129.4, 128.9, 127.4, 124.9, 123.5, 119.8, 117.7, 
117.1, 37.2.
AfinidAd LXX, 562, Abril-Junio 2013 141
14-Phenyl-14H-dibenzo[a,j]xanthene 4b
1H NMR (400 MHz, CDCl3): d = 8.34 (d, 2H, J = 8.41 Hz), 
7.79-6.94 (m, 15H, aromatic), 6.39 (s, 1H, CH); 13C NMR 
(100 MHz, CDCl3): d = 148.9, 146.3, 131.3, 130.8, 130.2, 
129.9, 129.5, 129.1, 128.6, 127.1, 126.7, 124.9, 123.5, 
119.8, 117.7, 117.1, 37.8.     
CONCLUSIONS   
We report an efficient and environment friendly procedure 
for the synthesis of 14-aryl-14H-dibenzo[a,j]xanthenes 
through one-pot condensation of β-naphthol with aryl 
halides in aqueous media catalyzed by some new bis-
piperidinium compounds. The experimental protocols are 
simple whereas the novel catalysts afforded high yields of 
the products. The present study also highlights the versa-
tile catalytic activity of less known bis-piperidinium com-
pounds.
 
ACKNOwLEDGEMENTS
We are thankful to Higher Education Commission Pakistan 
for the financial support.
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Table 1. Condensation of β-naphthol and aldehydes
Entry R Product Catalyst 1a (Yield %) Catalyst 2a
(Yield %)
Mp (oC)/(lit.)
1 4-Br.C6H4 4a 90 93 295 (296) [20]
2 C6H5 4b 88 89 181 (181-183) [21]
3 4-CH3.C6H4 4c 89 91 227 (228-229) [17]
4 4-OCH3.C6H4 4d 91 92 202 (202-203) [17]
5 2-NO2.C6H4 4e 82 81 214 (213-214) [21]
6 3-NO2.C6H4 4f 87 89 209-211 (211-212) [17]
7 4-NO2.C6H4 4g 98 97 310-311 (311-312) [21]
8 4-Cl.C6H4 4h 88 90 287-288 (288-289) [17]
9 2- Cl.C6H4 4i 81 84 214-215 (215-216) [17]
10 2,4-Cl2.C6H3 4j 87 86 228 (227) [22]
11 4-OH.C6H4 4k 82 86 139-140 (140) [23]
12 Me2CH 4l 67 62 152-153 (153-154) [17]
13 CH3CH2 4m 64 69 149 (151) [17]
aβ-naphthol and aldehydes (2:1) was carried out using 15 mol% catalyst loading at 100oC in wa-
ter for 3 hours (sufficient time for the completion of reaction as indicated by TLC)


Efficient, one-pot synthesis of 14-aryl-14Hdibenzo[a, j]xanthenes in aqueous medium catalyzed by bis-piperidinium compounds

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