International Journal of Organic Chemistry, 2013, 3, 275-279
Published Online December 2013 (http://www.scirp.org/journal/ijoc)
http://dx.doi.org/10.4236/ijoc.2013.34039
Open Access IJOC
Solvent-Free Synthesis of 5-Alkenyl-2,2-butylidene-1,
3-dioxane-4,6-diones under Ultrasonic Irradiation
with o-Phthalimide-N-Sulfonic Acid as Catalyst
Chunhua Lin, Zhaohui Xu, Weilin Liao
Fine Chemical Key Laboratory of Jiangxi Province, Nanchang, China
Received October 20, 2013; revised November 25, 2013; accepted December 11, 2013
Copyright © 2013 Chunhua Lin et al. This is an open access article distributed under the Creative Commons Attribution License,
which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
ABSTRACT
5-Alkenyl-2,2-butylidene-1,3-dioxane-4,6-diones were synthesized by the Knoevenagel condensation reaction of aro-
matic aldehydes with 2,2-butylidene-1,3-dioxane-4,6-dione using o-phthalimide-N-sulfonic acid as catalyst, without
solvent under ultrasonic irradiation. The present method has some notable advantages such as mild reaction conditions,
short reaction times, less catalyst dosage and high yields with the green aspects by avoiding toxic catalysts and solvents.
Further, the catalyst can be reused for five times without any noticeable decrease in the catalytic activity.
Keywords: o-Phthalimide-N-Sulfonicacid; 5-Alkenyl-2,2-butylidene-1,3-dioxane-4,6-diones; Aromatic Aldehydes;
Knoevenagel Condensation
1. Introduction
In recent years, the preparation of 5-alkenyl-1,3-dioxane-
4,6-diones has attracted strong interest owing to the
broad spectrum of their properties: these compounds can
be employed as versatile intermediates for a series of
natural products and heterocyclic compounds with poten-
tially biological activity [1-5]. In addition, it is also re-
acted with Grignard reagent in conjugate addition [6] or
conjugated dienes in Diels-Alder cycloaddition [7]. In
particular, 5-alkenyl-2,2-dimethyl-1,3-dioxane-4,6-dione
is an important reagent for synthesizing lipid-lowering
drugs “Lipitor” [8]. Therefore, the preparation of 5-al-
kenyl-1,3-dioxane-4,6-diones is of much current impor-
tance.
More recently, lots of methods for the synthesis of 5-
alkenyl-1,3-dioxane-4,6-diones have been reported in the
literature. Generally, they were synthesized by the Kno-
evenagel condensation reaction of 1,3-dioxane-4,6-
diones and aromatic aldehydes in the presence of bases
such as pyridine [9,10], piperidine/glacial acetic acid [11,
12], or hexamethyldisilazane [13] and Lewis acids, such
as anhydrous zinc chloride [14], TiCl4/pyridine [15] and
CePW12O40 [16]. However, many of these methodologies
have not been entirely satisfactory, owing to such draw-
backs as low yields, long reaction time, more catalyst
dosage, environmentally unfavorable solvents, emerging
the problems of tedious work-up and effluent pollution.
Uncatalyzed reaction was also reported in the literature
using DMF or DMSO as solvent, which is toxic, terato-
genic and suspected carcinogen. Those methods gave
mixtures of unsaturated and Michael addition products
[17]. Thus, a mild, efficient, and environmentally friendly
method using economical catalyst is desirable.
Recently, the solvent-free condition and the use of het-
erogeneous catalysts have emerged as an eco-friendly al-
ternative of great importance within organic synthesis, as
they reduce environmental pollution and bring down han-
dling costs due to simplification of work-up technique
[18].
Ultrasound has increasingly been used in organic syn-
thesis in the last three decades. Compared with tradi-
tional methods, the procedure is more convenient and can
be carried out in higher yields, shorter reaction time or
milder conditions under ultrasound irradiation [19-23].
Our investigations on the application of ultrasound in or-
ganic synthesis [16] and our work on Knoevengel con-
densations [13,24] are continued. Herein, we would like to
report an efficient and practical procedure for the synthe-
sis of 5-alkenyl-2,2-butylidene-1,3-dioxane-4,6-diones
with 2,2-butylidene-1,3-dioxane-4,6-dione [23,25] and

C. H. LIN ET AL.
276
aromatic aldehydes in o-phthalimide-N-sulfonic acid
(OPNSA) without solvent under ultrasound irradiation
(Scheme 1).
2. Results and Discussion
To optimize the reaction conditions, a selected model
reaction was carried out with 2,2-butylidene-1,3-dioxane-
4,6-dione 1 (0.01 mol, 1.7 g), benzaldehyde 2 (0.01 mol)
and different sets of reaction conditions. The results are
summarized in Table 1. The results clearly show that the
catalyst is essential, the catalytic activity of o-phthalim-
ide-N-sulfonic acid (OPNSA) is high, giving 3a in high
yield in a short reaction time. Using OPNSA as the cata-
lyst, we evaluated the reaction in various solvents and
under solvent-free conditions. The product yield in a po-
lar solvent was higher than the one in non-polar solvent,
but under solvent-free conditions the highest yield was
obtained (Table 1, Entries 1-8). The catalyst (OPNSA)
plays a crucial role in the success of the reaction in terms
of the yields. The presence of 0 mol% OPNSA gave the
product 3a in quantitative yield (35%) at 60˚C. Increas-
ing the catalyst to 1, 3, and 5 mol% results in improved
reaction yields to 76%, 89% and 87% respectively (Ta-
ble 1, Entries 8-11). Use of just 3 mol% OPNSA is suf-
ficient to push the reaction forward. Higher amounts of
the catalyst did not improve the results to a great extent.
Thus, 3 mol% OPNSA was chosen as a quantitative cata-
lyst for these reactions.
To find the optimum reaction time, the reaction was
carried out in the presence of OPNSA for 20, 30, 40 and
60 minutes, resulting in the isolation of 3a in 90%, 91%,
90% and 89% yield, respectively. Similarly, the optimum
reaction temperature was 30˚C. In addition, it must be
pointed out that all of these reactions were carried out
without solvent under ultrasonic irradiation. Under me-
chanical agitation conditions the product yield for 68%
and with ultrasonic irradiation the product yield for 91%,
which indicated the ultrasonic radiation to promote the
reaction effectively (Table 1, Entries 16, 17). The best
results was obtained when was conducted at 30˚C, for 30
minutes in the presence of 3 mol% OPNSA (Table 1,
Entry 16).
To determine the generality of this method, the scope
of the reaction was investigated using a number of aro-
matic aldehydes under the optimized reaction conditions.
The results are presented in Table 2. The results show
benzaldehyde and aromatic aldehydes with electron with
drawing groups (-Cl, -NO2, -F) and electron-donating
groups (-OCH3, -OH, -N(CH3)2) have all provided high
yields of the products.
The principle advantages of the use of o-phthalimide-
N-sulfonic acid (OPNSA) in organic transformations are
their reusability. The catalyst was readily recovered from
Table 1. Optimization of reaction conditions for synthesiz-
ing compound (3a)a.
Entry SolventCatalyst
(mol%)
Temperature
(˚C)
Time
(min)
Yieldb
(%)
Experiment
method
1C
2H5OH3 Reflux 120 81 Ultrasonic
2CH
3OH3 Reflux 120 80 Ultrasonic
3CH
3CN3 Reflux 150 72 Ultrasonic
4THF 3 Reflux 150 73 Ultrasonic
5C
6H6 3 Reflux 180 66 Ultrasonic
6CH
2Cl23 Reflux 210 68 Ultrasonic
7H
2O 3 Reflux 120 78 Ultrasonic
8None 3 60 60 89 Ultrasonic
9None 5 60 60 87 Ultrasonic
10None 1 60 60 76 Ultrasonic
11None 0 60 120 35 Ultrasonic
12None 0 60 120 24 Mechanical
13None 3 50 60 89 Ultrasonic
14None 3 40 40 90 Ultrasonic
15None 3 30 30 91 Ultrasonic
16None 3 30 20 90 Ultrasonic
17None 3 30 60 68 Mechanical
aReaction conditions: benzaldhyde (0.01 mol), 2,2-butylidene-1,3-dioxane-
4,6-dione (1.70 g, 0.01 mol), solvent (10 mL) or solvent-free conditions
(power ultrasonic irradiation 250 W, irradiation frequency 40 kHz); bIso-
lated yields.
Scheme 1. Synthesis of 5-alkenyl-2,2-butylidene-1,3-diox-
ane-4,6-diones.
the reaction mixture using the procedure outlined in the
experimental section. The separated catalyst was washed
with 2-methoxy-2-methylpropane (10 mL), it was di-
rectly used in a similar reaction. From Table 3 we found
that the catalyst could be used at least five times with
only a slight reduction in activity (91% yield for first use,
91% for second use, 90% for third use, 89% for fourth
time and 86% for fifth time).
A plausible mechanism for the formation of the 5-al-
kenyl-2,2-butylidene-1,3-dioxane-4,6-diones products using
o-phthalimide-N-sulfonic acid (OPNSA) as a catalyst has
been depicted in Scheme 2.
Open Access IJOC

C. H. LIN ET AL. 277
Table 2. OPNSA-catalyzed synthesis of 5-alkenyl-2,2-bu-
tylidene-1,3-dioxane-4,6-diones (3a-3h)a.
Melting point()℃
R Product Time (min)
Yieldb
(%) Found Reported [Ref.]
C6H5 3a 30 91 87 - 88 88 - 90 [26]
4-HO-C6H4 3b 35 88 170 - 172 170 - 172 [26]
4-CH3O-C6H4 3c 35 89 83 - 85 83 - 85 [16]
4-NO2-C6H4 3d 15 93 150 - 152 150 - 152 [16]
2-NO2-C6H4 3e 20 91 112 - 114 113 - 115 [16]
4-F-C6H4 3f 15 87 86 - 88 86 - 88 [26]
4-Cl-C6H4 3g 20 84 115 - 116 114 - 116 [16]
4-(CH3)2N-C6H4 3h 25 92 180 - 182 180.5 - 181 [16]
aReaction conditions: benzaldhyde (0.01 mol), 2,2-butylidene-1,3-dioxane-4,
6-dione (1.70 g, 0.01 mol), OPNSA catalyst (3 mol%), 30˚C, solvent-free
conditions (power ultrasonic irradiation 250 W, irradiation frequency 40
kHz); bIsolated yields.
Table 3. The recycling of OPNSA in synthesis of 3a under
the reaction optimized conditions.
Entry Time (min) Yielda (%)
1 30 91
2 35 91
3 35 90
4 38 89
5 40 86
aIsolated yields.
Scheme 2. The plausible mechanism for synthesis of the 5-
alkenyl-2,2-butylidene-1,3-dioxane-4,6-diones.
3. Conclusion
The catalyst of o-phthalimide-N-sulfonic acid (OPNSA),
showed high catalytic activity in the synthesis of 5-al-
kenyl-2,2-butylidene-1,3-dioxane-4,6-diones synthesized
by the Knoevenagel condensation reaction of aromatic
aldehydes with 2,2-butylidene-1,3-dioxane-4,6-dione
without solvent under ultrasonic irradiation. This proce-
dure offers several advantages over the other techniques
available in the literature, including much shorter reac-
tion times, higher yields, milder conditions, and the ab-
sence of any hazardous organic solvents, which makes it
a useful and attractive protocol for the synthesis of these
compounds. Furthermore, the catalyst could be recycled
after a simple work-up, and used at least five times with-
out significant reduction in its catalytic activity.
4. Experimental Section
4.1. Reagents and Instruments
All chemicals were purchased from Aladdin, Aldrich and
Fluka Chemical Companies and without further purifica-
tion. The melting points of the various compounds were
measured by XT-4 digital micro melting point instrument
and are uncorrected. Reaction monitoring was accompa-
nied by TLC using silica gelSIL G/UV 254 plates. KQ-
250E-machine ultrasonic instrument is made in Kunshan
Co., LTD. IR spectra were taken on a Nicolet-360 FT-IR
spectrometer by incorporating samples in KBr disks.
1HNMR spectra were recorded with Bruker Avance 400
MHz spectrometer with CDCl3 as the solvent and TMS
as the internal standard. The 13CNMR data were col-
lected on Bruker Avance 100 MHz instrument with
CDCl3 as the solvent and TMS as the internal standard.
4.2. Preparation of o-Phthalimide-N-Sulfonic
Acid (OPNSA)
A solution of chlorosulfonic acid (11.6 g, 0.1 mol) in
CH2Cl2 (20 ml) was added to o-Phthalimide (14.7 g, 0.1
mol) in CH2Cl2 (20 ml) solution at 0˚C. Then the mix-
ture was stirred at room temperature for 24 h. The sol-
vent was evaporated at reduced pressure and the remain-
ing solid was washed with 2-methoxy-2-methylpropane
(3 × 10 mL) and filtered to give the desired product as a
yellow solid material in 97% yield.
4.3. General Procedure for Synthesis of
5-Alkenyl-2,2-butylidene-1,3-dioxane-4,
6-diones
2,2-butylidene-1,3-dioxane-4,6-dione 1 (0.01 mol, 1.7 g),
aromatic aldehyde 2 (2a-2h, 0.01 mol) and o-phthalim-
ide-N-sulfonic acid (OPNSA) 3 mol% were taken in a
round bottom flask, then the mixture was stirred under
ultrasound irradiation at room temperature for 15 - 35
min. Upon completion of the reaction, as confirmed by
thin-layer chromatography (petroleum ether/ethyl acetate
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C. H. LIN ET AL.
278
5:1), the reaction mixture was diluted with 20 mL etha-
nol. The catalyst was collected from the filtrate, which
was concentrated on reduced pressure. After the remain-
ing catalyst was washed with 2-methoxy-2-methylpro-
pane (10 mL), it was directly used for the next reaction.
The crude solid product was filtered and then purified by
recrytallization from ethanol to afford the pure product 3
(3a-3h). The physical data (mp, IR, NMR) of known
compounds were identical to the corresponding literature
data.
4.4. The Data for Representative Compounds
5-Benzylidene-2 ,2-butyliden e-1,3-dioxane-4,6-dione (Co-
mpound 3a, Table 1): White solid (yield: 91%), M.p.
87˚C - 88˚C; IR

max (KBr): 2951, 1763, 1734, 1626,
1571, 741,693 cm−1; 1H NMR (CDCl3, 400 MHz):
 8.37
(s, 1H), 8.02 (d, J = 7.14 Hz, 2H), 7.56 - 7.47 (m, 3H),
2.22 (s, 4H), 1.89 (s, 4H); 13CNMR (CDCl3, 100 MHz):
δ163.86, 160.48, 157.65, 133.65, 133.49, 131.68, 128.76,
115.71, 113.75, 38.54, 23.28.
5-(4-Hydroxybenzylidene)-2,2- butylidene-1,3- dioxane-
4,6-dione (Compound 3b, Table 1): White solid (yield:
88%), M.p. 170˚C - 172˚C; IR

max (KBr): 2965, 2957,
1750, 1700, 1638, 1537, 1400, 1170, 800 cm−1; 1H NMR
(CDCl3, 400 MHz):
 8.35 (s, 1H), 8.12 (d, J = 8.82 Hz,
2H), 6.94 (d, J = 8.82 Hz, 2H), 2.24 - 2.19 (m, 4H), 1.90
- 1.85 (m, 4H); 13CNMR (CDCl3, 100 MHz,): δ 164.93,
162.17, 158.37, 137.88, 124.43, 116.21, 113.67, 110.94,
38.41, 23.26.
5-(4-Methoxybenzylidene)-2,2- butylidene-1,3- dioxane-
4,6-dione (Compound 3c, Table 1): White solid (yield:
89%), M.p. 83˚C - 85˚C; IR

max (KBr): 2972, 2901,
1756, 1718, 1624, 1573, 1455, 1381, 1183, 800 cm−1; 1H
NMR (CDCl3, 400 MHz):
 8.32 (s, 1H),8.19 (d, J = 8.97
Hz, 2H), 6.98 (d, J = 8.97 Hz, 2H), 3.90 (s, 3H), 2.23 -
2.18 (m, 4H), 1.90 - 1.85 (m, 4H); 13CNMR (CDCl3, 100
MHz,): δ 164.62, 161.19, 157.56, 137.48, 124.71, 114.38,
113.37, 111.65, 55.68, 38.41, 23.26.
5-(4-Nitrobenzylidene)-2,2-butylidene-1,3-dioxane-4,6-
dione (Compound 3d, Table 1): Pale yellow solid (yield:
93%), M.p. 150˚C - 152˚C; IR

max (KBr): 2976, 2901,
1763, 1731, 1626, 1605, 1524, 1350, 800 cm−1; 1H NMR
(CDCl3, 400 MHz):
 8.41 (s, 1H), 8.30 (d, J = 8.82 Hz,
2H), 8.06 (d, J = 8.70 Hz, 2H), 2.27 - 2.23 (m, 4H), 1.95
- 1.90 (m, 4H); 13CNMR (CDCl3, 100 MHz): δ 162.36,
159.36, 153.67, 149.26, 137.11, 132.73, 123.30, 119.17,
114.08, 36.43, 23.00.
5-(2-Nitrobenzylidene)-2,2-butylidene-1,3-dioxane-4,6-
dione (Compound 3e, Ta ble 1): Pale yellow solid (yield:
91%), M.p. 112˚C - 114˚C; IR 
max (KBr): 2963, 2908,
1765, 1736, 1625, 1604, 1524, 1363, 800 cm−1; 1H NMR
(CDCl3, 400 MHz):
 8.75 (s, 1H), 8.28 (d, J = 8.22 Hz,
1H), 7.78 - 7.62 (m, 2H), 7.49 (d, J = 7.56 Hz, 1H), 2.24
- 2.21 (m, 4H), 1.91 - 1.89 (m, 4H); 13CNMR (CDCl3,
100 MHz): δ 161.69, 159.22, 155.09, 145.99, 133.46,
130.57, 129.99, 129.39, 124.44, 118.19, 114.14, 38.23,
22.87.
5-(4-Furylmethylene)-2,2-butylidene-1,3-dioxane-4,6-
dione (Compound 3e, Tabl e 1 ): White solid (yield: 87%),
M.p. 86˚C - 88˚C; IR

max (KBr): 2961, 2943, 1757, 1726,
1598, 1604, 1508, 1364, 1081, 840, 804 cm−1; 1H NMR
(CDCl3, 400 MHz):  8.33 (s, 1H), 8.14 (d, J = 5.58, 8.64
Hz, 2H), 7.16 (t, J = 8.61 Hz, 1H), 2.24 - 2.19 (m, 4H),
1.91 - 1.86 (m, 4H); 13CNMR (CDCl3, 100 MHz,): δ
167.44, 164.01, 163.81, 160.54, 156.21, 136.73, 136.60,
128.07, 128.03, 116.27, 115.98, 114.99, 114.96, 113.74,
38.49, 23.24.
5. Acknowledgements
The authors thank the financial support from the National
Science and Technology Project (No. 2001BA323C) and
the Graduate Innovation Foundation of Jiangxi Province
(No.YC10A051).
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