Camphor-10-sulfonic acid catalyzed condensation of 2-naphthol with aromatic/aliphatic aldehydes to 14-aryl/alkyl-14H-dibenzo[a,j]xanthenes

Article abstract of DOI:10.2298/JSC130805021K

The (±)-camphor-10-sulfonic acid (CSA) catalyzed condensation of 2-naphthol with both aliphatic/aromatic aldehydes at 80 °C yielded 14-alkyl/ /aryldibenzoxanthenes as the sole products in high yields. However, the same condensation with benzaldehyde at 25

Full text of DOI:10.2298/JSC130805021K

J. Serb. Chem. Soc. 79 (9) 1051–1058 (2014) UDC 547.599.6+547.269.3+544.4:547.655.1:
JSCS–4646
547.571:547.815.4
Original scientific paper
Camphor-10-sulfonic acid catalyzed condensation of
2-naphthol with aromatic/aliphatic aldehydes to
14-aryl/alkyl-14H-dibenzo[a,j]xanthenes
*
KSHAMA KUNDU and SANDIP K. NAYAK
Bioorganic Division, Bhabha Atomic Research Centre, Mumbai – 400085, India
(Received 5 August, revised 3 October 2013, accepted 12 March 2014)
Abstract: The (±)-camphor-10-sulfonic acid (CSA) catalyzed condensation of
2-naphthol with both aliphatic/aromatic aldehydes at 80 °C yielded 14-alkyl/
/aryldibenzoxanthenes as the sole products in high yields. However, the same
condensation with benzaldehyde at 25 °C afforded a mixture of the inter-
mediate 1,1-bis-(2-hydroxynaphthyl)phenylmethane and 14-phenyldibenzo-
xanthene, while the condensation with aliphatic aldehydes at 25 °C furnished
the corresponding 14-alkyldibenzoxanthenes as the sole products. Moreover,
the condensation of 2-naphthol with aromatic/aliphatic aldehydes with low
catalyst loading (2 mol %) was greatly accelerated under microwave irradiation
to afford the corresponding 14-aryl/alkyldibenzoxanthenes as the sole products
in high yields.
Keywords: dibenzoxanthenes; β-naphthol; (±)-camphor-10-sulfonic acid; mic-
rowave irradiation.
INTRODUCTION
Xanthenes and benzoxanthenes are important biologically active hetero-
1
cycles as they possess several important bioactivities including antiviral, anti-
2
3
inflammatory, and antibacterial activities. Furthermore, these heterocycles are
4
5
used as sensitizers in photodynamic therapy, leuco dyes in laser technology,
antagonists of the paralyzing action of zoxazolamine (2-amino-5-chlorobenzo-
6
xazole) and pH-sensitive fluorescent materials for the visualization of biomole-
7
cules. Therefore, the synthesis of various xanthene derivatives is of great syn-
thetic importance. Several methods have been reported for the synthesis of xan-
8
thenes and benzoxanthenes, which include trapping of benzynes with phenols,
9
cyclodehydration, cyclocondensation of 2-hydroxyaromatic aldehydes with 2-tet-
ralone and intramolecular phenyl carbonyl coupling reactions of benzaldehydes
10
*Corresponding author. E-mail: sknayak@barc.gov.in
doi: 10.2298/JSC130805021K
1051
Available online at: www.shd.org.rs/jscs/
___________________________________________________________________________________________________________________________
(C) 2014 SCS. All rights reserved.

1052
KUNDU and NAYAK
11
and acetophenones. In addition, 14-aryl-14H-dibenzo[a,j]xanthenes and related
compounds have been synthesized from the reaction of 2-naphthol with form-
12
13
14
amide, 1-(hydroxymethyl)naphthalen-2-ol and carbon monoxide. More-
15
16
17
over, various catalysts, including TaCl , Sr(OTf) , Yb(OTf) , sulfamic
5
2
21
3
18
19
20
acid, iodine, Amberlyst-15, cyanuric chloride, ceric ammonium nitrate
22
23
24
25
26
(CAN), BF :SiO , P O or InCl , Sc[N(SO C F ) ] , RuCl ·nH O,
3
2
2
5
3
2 8 17 2 3
3
2
27
28
poly(ethylene glycol)–SO H (PEG)–SO H, an ionic liquid, dodecylphos-
phonic acid (DPA) or dodecylsulfamic acid (DSA), nano-silica phosphoric acid
(nano-SPA), nano-SnCl ·SiO , 4-dodecylbenzenesulfonic acid (DBSA),
3
3
29
30
31
32
4
2
33
34
tungstophosphoric acid and a functionalized mesoporous material were found
to catalyze condensation reactions of 2-naphthol with different aldehydes to
afford 14-substituted-14H-dibenzo[a,j]xanthenes. However, many of the reported
methodologies suffered from one or more disadvantages, such as long reaction
time, use of toxic and expensive catalysts, harsh reaction conditions, etc. Bearing
this in mind, as well as the increasing importance of benzoxanthenes in the phar-
maceutical industry, there is still a necessity for the development of an efficient,
environmentally benign and inexpensive catalyst for their synthesis. Herein, a
convenient microwave-assisted synthesis of 14-aryl/alkyl-14H-dibenzo[a,j]xan-
thenes from 2-naphthol and aromatic/aliphatic aldehydes using (±)-camphor-10-
-sulfonic acid as a catalyst is reported.
RESULTS AND DISCUSSION
Camphor-10-sulfonic acid (CSA) is an inexpensive and easy to handle
organo-catalyst that has been used in various organic transformations. Recently,
it was observed that CSA is a highly efficient catalyst for the activation of imines
35
in the Mannich type reaction of enolizable ketones. As an extension to this
work, it was considered of interest to explore its catalytic potential for the acti-
vation of aldehydes in the condensation of 2-naphthol with aldehydes to afford
dibenzoxanthenes. In a preliminary study, the reaction of 2-naphthol (1) with
benzaldehyde (2a, 0.55 equiv.) was performed at ambient temperature (25 °C)
with (±)-CSA (5 mol. %) under solvent-free conditions. The reaction was found
to be very sluggish as both the intermediate bis-(2-hydroxy-1-naphthyl)phe-
nylmethane (3a) as well as 14-phenyl-14H-dibenzo[a,j]xanthene (4a) were iso-
lated in 55 and 10 % yields, respectively, along with unreacted 1 (≈18 %) and 2a
(≈10 %) after stirring for 24 h (Table I, entry 1). Compounds 3a and 4a were
1
13
characterized by physical and spectroscopic (IR, H-NMR, C-NMR and MS)
data. Increasing the catalyst loading (10 mol %) (25 °C, 24 h) led to marginal
improvements in the yields of both 3a and 4a, although small amounts of the
respective starting materials were still recovered (Table I, entry 2).
However, with 20 mol % catalyst, both starting compounds were consumed
while 3a and 4a were isolated in 75 and 21 % yields, respectively (Table I, entry
Available online at: www.shd.org.rs/jscs/
___________________________________________________________________________________________________________________________
(C) 2014 SCS. All rights reserved.

CONDENSATION OF 2-NAPHTHOL WITH AROMATIC/ALIPHATIC ALDEHYDES
1053
3). In order to improve the yield and selectivity of the desired product 4a, the
above reaction was performed at an elevated temperature (80 °C) with 10 mol %
CSA as the catalyst. Gratifyingly, both the starting materials 1 and 2a were con-
sumed and 4a was isolated as a sole product in 81 % yield, while the intermediate
3a was found to be absent (Table I, entry 4). Further increase in catalyst loading
(15 mol %) led to completion of the reaction within 2 h at 80 °C to yield 4a as
the sole product in 89 % yield (Table I, entry 5).
TABLE I. Optimization of the reaction conditions for the (±)-CSA-catalyzed condensation of
2-naphthol (1) with benzaldehyde (2a)
Yield, %b
Entry
Reaction conditionsa
(±)-CSA, mol. %
Time, h
3a
4a
1
2
3
4
5
6
7
8
9
a
25 °C
25 °C
25 °C
80 °C
80 °C
5
10
20
10
15
10
5
24.0
24.0
16.0
8.0
55
63
75
–
–
–
–
–
–
10
14
21
81
89
89
88
88
0
2.0
MWI, 63–64 °C
MWI, 63–64 °C
MWI, 63–64 °C
MWI, 63–64 °C
0.25
0.25
0.25
0.50
2
0
b
2-Naphthol was reacted with benzaldehyde (0.55 equiv.) under solvent-free conditions; isolated yields
Microwave irradiation (MWI) is known to be an important tool in organic
synthesis to improve the selectivity, rate enhancement and reduction of thermal
36
degradative byproducts. To reduce the catalyst loading as well as the reaction
time required for the condensation at high temperature, reaction of 1 with 2a
(0.55 equiv.) was performed without solvent using a varied amount of (±)-CSA
(2–10 mol %) under MWI (400 W, 63–64 °C) when 4a was obtained as the sole
product in 88–89 % yields (Table I, entries 6–8). The reaction without using CSA
as catalyst did not yield any product 4a and both the starting compounds were
recovered. (Table I, entry 9). As evidenced from Table I, optimal catalyst loading
for the microwave-assisted condensation was found to be 2 mol %, affording 4a
in 88 % yield and therefore the same conditions were used for all subsequent
reactions.
To see the scope and generality of this microwave-assisted protocol, CSA
catalyzed condensation of 2-naphthol with a variety of aromatic aldehydes
(2b–k) was investigated under MWI. In all the cases, the desired dibenzoxan-
Available online at: www.shd.org.rs/jscs/
___________________________________________________________________________________________________________________________
(C) 2014 SCS. All rights reserved.

1054
KUNDU and NAYAK
thenes were obtained (Scheme 1) in good to high yields and the results are sum-
marized in Table II. In the case of solid aromatic aldehydes, such as 4-cyanoben-
–1
zaldehyde (2h), acetonitrile (0.25 ml mmol ) was used as solvent to make a uni-
form slurry, when the corresponding cyano dibenzoxanthene 4h was isolated in
86 % yield. Solvent optimization of this reaction with other microwave-active
solvents, viz. H O and DMF without changing catalyst loading was also investi-
2
gated. To this end, the use of H O led to the formation of 4h, albeit in poor yield
2
(32 %), while no product was detected using DMF as solvent, when both starting
compounds were recovered.
Scheme 1. Reaction scheme with structures of reactants 2b–k and products 4b–k.
TABLE II. Microwave assisted, (±)-CSA catalyzed condensation of 2-naphthol (1) with
aromatic aldehydes (ArCHO) to 14-aryl-14H-dibenzo[a,j]xanthene (4b–k); reaction con-
ditions: 2-naphthol, aldehydes (0.55 equiv.) and (±)–CSA (0.02 equiv.) were irradiated in a
microwave reactor at 400 W, 63–64 °C for 15–45 min
Melting point, °C
Entry
Aldehydes
Product
Time, min Yield, %a
Found
Reported
1
2
3
4
2b
2c
2d
2e
2f
2g
2h
2i
4b
4c
4d
4e
4f
4g
4h
4i
30
15
45
15
45
45
30
30
30
30
82
98
54
88
61
86
86
85
84
95
293–294
177–178
258–259
207–208
138–139
153–154
294–295
>300
295–296
179–180
258–260
205–206
138–140
–
291–292
–
310–311
259
5b
6b
7b
8b
9b
2j
2k
4j
4k
>300
256–257
10
a
b
-1
Isolated yields; acetonitrile (0.25mL mmol ) was used to make a uniform reaction mixture
The electronic effect of the substituents in the aromatic aldehydes was found
to have a minimal effect, as evidenced by the high yield of the corresponding
dibenzoxanthenes in almost all the cases (4b–k) (Table II, entries 1–10). How-
ever, the moderate yield of 4d derived from 2-methoxybenzaldehyde (2d) could
Available online at: www.shd.org.rs/jscs/
___________________________________________________________________________________________________________________________
(C) 2014 SCS. All rights reserved.

CONDENSATION OF 2-NAPHTHOL WITH AROMATIC/ALIPHATIC ALDEHYDES
1055
be explained by the large steric strain (resulting from the bulky methoxy group)
involved during the cyclodehydration step to dibenzoxanthene (Table II, entry 3).
To explore the generality of the catalyst, CSA catalyzed condensation of
2-naphthol (1) with aliphatic aldehydes was also investigated. In contrast to benz-
aldehyde, the CSA catalyzed (10 mol %) condensation of 1 with hexanal (2l) at
25 °C without solvent (24 h) led to complete consumption of starting materials
and 14-pentyldibenzoxanthene (4l) was obtained as the sole product in 73 %
yield; no trace of 1,1-bis(2-hydroxynaphthyl)hexane was detected (Scheme 2).
Similarly, the reaction with octanal (2m) led to the formation of 14-heptyldiben-
zoxanthene (4m) as the only product. However, at a higher temperature (80 °C),
both the reactions (with hexanal and octanal) were completed within 20 min
using a lower catalyst loading (5 mol %) to afford the corresponding dibenzoxan-
thenes in 93 and 86 % yields, respectively (Scheme 2). Moreover, the above
reactions under MWI were completed in 15 min with a lower catalyst loading (2
mol %), as compared to the high temperature reactions, affording the corres-
ponding dibenzoxanthenes (4l and 4m) in 92 and 95 % yields, respectively
24–26,29
(Scheme 2). Most catalysts
reported so far for the condensation of 1 with
aliphatic aldehydes furnished the corresponding dibenzoxanthenes in longer reac-
tion times and in moderate yields. Therefore, CSA displayed its catalytic effi-
ciency in the faster condensation of 1 with both aliphatic and aromatic aldehydes
to afford corresponding alkyl/aryl substituted dibenzoxanthenes in high yields.
Incidentally, the catalytic potential of CSA in terms of reaction time and yield
was found to be superior/similar to most of the hitherto reported catalysts.
Scheme 2. (±)-CSA-catalyzed condensation of 2-naphthol (1) with aliphatic aldehydes
(RCHO) to 14-alkyl-14H-dibenzo[a,j]xanthene (4l,m).
Compound 3a, obtained from the condensation of 1 and 2a at ambient
temperature, belongs to the important class of tethered bis(2-naphthol)s, which in
principle could be exploited further for the synthesis of a variety of macrocycles,
including crown ethers. To this end, reaction of 3a with pentaethyleneglycol
ditosylate and K CO in acetonitrile yielded the corresponding crown ether 5 in
2
3
good yield (Scheme 3).
Available online at: www.shd.org.rs/jscs/
___________________________________________________________________________________________________________________________
(C) 2014 SCS. All rights reserved.

1056
KUNDU and NAYAK
Scheme 3. Synthesis of bis-napthalenocrown-6.
EXPERIMENTAL
Microwave irradiation (MWI) was performed with an Anton Paar microwave reactor
(model SYNTHOS 3000). The melting points were determined using a Fisher–Johns melting
point apparatus and are uncorrected. The IR spectra were scanned with a Jasco FT IR 4100
1
spectrophotometer. The H- and 13C-NMR spectra were recorded with a Bruker AC 200/300
1
MHz spectrometer. Spectra were referenced to the residual chloroform (δ 7.25 ppm, H; 77.0
ppm, 13C). The low-resolution mass spectra were recorded on a Varian 500 mass spectrometer
(ESI/APCI) and a Shimadzu GC-MS 2010 mass spectrometer (EI 70 eV). The high-resolution
mass spectra were recorded on a Q-TOF (YA-105) micromass spectrometer (ESI, Ar) and a
Bruker maXis impact mass spectrometer (ESI). The microanalyses were realized using a
Vario Micro elemental analyzer. (±)-Camphor-10-sulfonic acid (CSA) was purchased from
Aldrich, USA, and was used as received. The spectral data of the known compounds were in
accordance with those reported in the literature, while the unknown compounds were char-
acterized by IR, NMR, HRMS and microanalytical data, which are given as Supplementary
Material to this paper.
Typical procedure for the solvent-free condensation of 2-naphthol (1) with benzaldehyde (2a)
to the dibenzoxanthene 4a
A mixture of 2-naphthol (1.44 g, 10.0 mmol), benzaldehyde (0.584 g, 5.50 mmol) and
(±)-CSA (0.192 g, 15.0 mol. %) was heated at 80 °C without any solvent. After completion of
the reaction (monitored by TLC), the formed pinkish solid was quenched with water, filtered,
washed with water and air-dried. The crude solid was recrystallized with hexane–ethyl
acetate, 9:1, to afford pure 4a (1.60 g, 89 %).
Typical procedure for the solvent-free condensation of 2-naphthol (1) with benzaldehyde (2a)
to the dibenzoxanthene 4a under microwave irradiation
A mixture of 2-naphthol (1.44 g, 10.0 mmol), benzaldehyde (0.584 g, 5.50 mmol) and
(±)-CSA (0.026 g, 2.0 mol. %) was placed in a microwave vessel and irradiated (400 W, 63–
–64 °C). After 15 min, TLC showed complete consumption of both the starting materials and
the formation of 4a as the only product. The thus formed solid was quenched with water,
filtered, washed with water and air-dried. The crude solid was recrystallized with hexane–
–ethyl acetate, 9:1, to afford pure 4a (1.59 g, 88 %).
Typical procedure for the synthesis of bis-napthocrown-6 (5) from 3a
A mixture of bis-(2-naphthol) 3a (0.790 g, 2.10 mmol), pentaethyleneglycol ditosylate
(1.26 g, 2.30 mmol, 1.1 equiv.) and Cs2CO3 (1.73 g, 5.30 mmol, 2.5 equiv.) in dry acetonitrile
(30 mL) was refluxed for 8 h when TLC showed the absence of both 3a and the ditosylate.
The solvent was removed under vacuo, cooled, quenched with 1 M HCl and extracted with
ethyl acetate. The organic layer was washed with water and brine, and dried (Na2SO4). Remo-
Available online at: www.shd.org.rs/jscs/
___________________________________________________________________________________________________________________________
(C) 2014 SCS. All rights reserved.

CONDENSATION OF 2-NAPHTHOL WITH AROMATIC/ALIPHATIC ALDEHYDES
1057
val of solvent afforded a thick mass which was purified by silica gel column chromatography
(using CHCl3 as the eluant) to afford pure 5 (0.948 g, 78 %).
CONCLUSIONS
In conclusion, a simple, efficient and microwave-assisted (15–45 min) pro-
tocol for the CSA-catalyzed condensation of 2-naphthol with aromatic/aliphatic
aldehydes to 14-aryl/alkyl-14H-dibenzo[a,j]xanthenes was developed. In contrast
to the poor yields of 14-alkyl-dibenzo[a,j]xanthenes from aliphatic aldehydes
with most of the reported catalysts, CSA was found to be a superior catalyst to
yield the corresponding dibenzoxanthenes in high yields. Shorter reaction time,
simple work-up procedure and easy isolation of the products in high yields are
some of the salient features of this new protocol. The intermediate bis(2-naph-
thol) derived from the condensation of 2-naphthol and benzaldehyde at ambient
temperature was used in the synthesis of a novel class of crown ethers.
SUPPLEMENTARY MATERIAL
The physical, analytic and spectral data for the prepared compounds as well as their 1H-
and 13C-NMR spectra are available electronically from http://www.shd.org.rs/JSCS/, or from
the corresponding author on request.
И З В О Д
КОНДЕНЗАЦИЈA 2-НАФТОЛА СА АРОМАТИЧНИМ/АЛИФАТИЧНИМ АЛДЕХИДИМА У
СИНТЕЗИ 14-АРИЛ/AЛКИЛ-14H-ДИБЕНЗО[a,j]КСАНТЕНА КАТАЛИЗОВАНА
КАМФОР-10-СУЛФОНСКОМ КИСЕЛИНОМ
KSHAMA KUNDU и SANDIP K. NAYAK
Bio-Organic Division, Bhabha Atomic Research Centre, Mumbai – 400085, India
(±)-Камфор-10-сулфонска киселина (CSA) катализује кондензацију 2-нафтола са
ароматичним/алифатичним алдехидима, на 80 °С у синтези 14-арил/aлкил-14H-дибен-
зо[a,j]ксантена као јединих производа, у високом приносу. У реакција кондензације са
бензалдехидом на 25 °С добија се смеша интермедијера бис(2-хидроксинафтил)-
фенилметанa и производa 14-фенил-дибензоксантенa, док кондензацијом са алифатич-
ним алдехидима на 25 °С настају 14-алкил-дибензоксантeни као једини производи.
Даље, кондензацијом 2-нафтола са ароматичним/алифатичним алдехидима у присуству
малих количина катализатора (2 mol %), под условима озрачивања микроталасима,
реакција се брже одвија и настају одговарајући 14-арил/алкилдибензоксантени као
једини производи.
(Примљено 5. августа, ревидирано 3. октобра 2013, прихваћено 12. марта 2014)
REFERENCES
1. R. W. Lambert, J. A. Martin, J. H. Merrett, K. E. B. Parkes, G. J. Thomas, PCT Int. Appl.
WO 9706178 (1997) (CA 126 P212377y)
2. J. P. Poupelin, G. Saint-Rut, O. Foussard-Blanpin, G. Narcisse, G. Uchida-Ernouf, R.
Lacroix, Eur. J. Med. Chem. 13 (1978) 67
3. T. Hideo, Jpn. Tokyo Koho JP 56004580 (1981) (CA 95 80922b)
4. R. M. Ion, A. Planner, K. Wiktorowicz, D. Frackowiak, Acta Biochim. Pol. 45 (1998) 833
Available online at: www.shd.org.rs/jscs/
___________________________________________________________________________________________________________________________
(C) 2014 SCS. All rights reserved.

1058
KUNDU and NAYAK
5. S. De, S. Das, A. Girigoswami, Spectrochim. Acta, A 61 (2005) 1821
6. G. Saint-Ruf, H.-T.-Hieu, J.-P. Poupelin, Naturwissenschaften 62 (1975) 584
7. C. G. Knight, T. Stephenes, Biochem. J. 258 (1989) 683
8. D. W. Knight, P. B. Little, J. Chem. Soc. Perkin Trans 1 15 (2001) 1771
9. C. A. Buehler, D. E. Cooper, E. O. Scrudder, J. Org. Chem. 8 (1943) 316
10. A. Jha, J. Beal, Tetrahedron Lett. 45 (2004) 8999
11. C.-W. Kuo, J.-M. Fang, Synth. Commun. 31 (2001) 877
12. J. A. V. Allan, D. D. Giannini, T. H. Whitesides, J. Org. Chem. 47 (1982) 820
13. R. N. Sen, N. Sarkar, J. Am. Chem. Soc. 47 (1925) 1079
14. K. Ota, T. Kito, Bull. Chem. Soc. Jpn. 49 (1976) 1167
15. A. K. Bhattacharya, K. C. Rana, M. Mujahid, I. Sehar, A. K. Saxena, Bioorg. Med. Chem.
19 (2009) 5590
16. J. Li, W. Tang, L. Lu, W. Su, Tetrahedron Lett. 49 (2008) 7117
17. W. Su, D. Yang, C. Jin, B. Zhang, Tetrahedron Lett. 49 (2008) 3391
18. B. Rajitha, B. Sunil Kumar, Y. Thirupathi Reddy, P. Narsimha Reddy, N. Sreenivasulu,
Tetrahedron Lett. 46 (2005) 8691
19. M. A. Pasha, V. P. Jayashankara, Bioorg. Med. Chem. Lett. 17 (2007) 621
20. S. Ko, C.-F. Yao, Tetrahedron Lett. 47 (2006) 8827
21. M. A. Bigdeli, M. M. Heravi, G. Hossein Mahdavinia, Catal. Commun. 8 (2007) 1595
22. A. Kumar, S. Sharma, R. A. Maurya, J. Sarkar, J. Comb. Chem. 12 (2010) 20
23. B. B. F. Mirjalili, A. Bamoniri, A. Akbari, Tetrahedron Lett. 49 (2008) 6454
24. R. Kumar, G. C. Nandi, R. K. Verma, M. S. Singh, Tetrahedron Lett. 51 (2010) 442
25. M. Hong, C. Cai, J. Fluorine Chem. 130 (2009) 989
26. K. Tabatabaeian, A. Khorshidi, M. Mamaghani, A. Dadashi, Synth. Commun. 41 (2011)
1427
27. D. Prasad, M. Nath, Catal. Sci. Technol. 2 (2012) 93
28. M. A. Zolfigol, V. Khakyzadeh, A. R. Moosavi-Zare, A. Zare, S. B. Azimi, Z. Asgari, A.
Hasaninejad, C. R. Chim. 15 (2012) 719
29. S. Ghassamipour, A. R. Sardarian, J. Heterocycl. Chem. 49 (2012) 669
30. A. Bamoniri, B. F. Mirjalili, S. Nazemian, Curr. Chem. Lett. 2 (2013) 27
31. B. F. Mirjalili, A. Bamoniri, M. A. Mirhoseini, Chem. Heterocycl. Compd. 48 (2012) 856
32. D. Prasad, A. Preetam, M. Nath, C. R. Chim. 15 (2012) 675
33. T. S. Rivera, M. N. Blanco, L. R. Pizzio, G. P. Romanelli, Green Chem. Lett. Rev. 5
(2012) 433
34. J. Mondal, M. Nandi, A. Modak, A. Bhaumik, J. Mol. Catal., A 363–364 (2012) 254
35. K. Kundu, S. K. Nayak, RSC Adv. 2 (2012) 480
36. a) S. Caddick, Tetrahedron 51 (1995) 10403; b) A. Lopuy, A. Petit, J. Hamelin, F.
Texier-Boulett, P. Jacquault, D. Mathe, Synthesis (1998) 1213.
Available online at: www.shd.org.rs/jscs/
___________________________________________________________________________________________________________________________
(C) 2014 SCS. All rights reserved.

Copyright of Journal of the Serbian Chemical Society is the property of National Library of
Serbia and its content may not be copied or emailed to multiple sites or posted to a listserv
without the copyright holder's express written permission. However, users may print,
download, or email articles for individual use.