The use of optically active O-alkyl ester hydrochlorides of L-phenylalanine and L-tyrosine as chiral micellar media for the catalysis of diels-alder reactions

Article abstract of DOI:10.4314/bcse.v31i3.15

The effect of a range of O-alkyl ester hydrochloride surfactants derived from L-phenylalanine and L-tyrosine as catalysts on the Diels-Alder reaction between cyclopentadiene and methyl acrylate was studied. Both chain lengths (C8-C14) and head groups of the surfactants were found to influence the yield and selectivity of the Diels-Alder product. The C10 derivatives of both phenylalanine and tyrosine surfactants gave the highest yields and selectivity. Phenylalanine ester hydrochlorides showed better catalytic activity than the tyrosine derivatives. Adduct optimum yield was obtained at a concentration relating to their critical micelle concentration (CMC) values. The Diels-Alder reaction was also found to be favored in acidic condition (pH 3) as well as in the presence of lithium chloride (LiCl) as salting out agent.

Full text of DOI:10.4314/bcse.v31i3.15

Bull. Chem. Soc. Ethiop. 2017, 31(3), 509-518.
2017 Chemical Society of Ethiopia and The Authors
DOI: http://dx.doi.org/10.4314/bcse.v31i3.15
ISSN 1011-3924
Printed in Ethiopia

THE USE OF OPTICALLY ACTIVE O-ALKYL ESTER HYDROCHLORIDES OF L-
PHENYLALANINE AND L-TYROSINE AS CHIRAL MICELLAR MEDIA FOR THE
CATALYSIS OF DIELS-ALDER REACTIONS
*
P. Caumul , P. Koonja, N. Namooya, A. Prayag, N. Joondan and S. Jhaumeer-Laulloo
Department of Chemistry, Faculty of Science, University of Mauritius, Réduit, Mauritius
(Received March 7, 2017; Revised December 15, 2017; Accepted December 18, 2017)
ABSTRACT. The effect of a range of O-alkyl ester hydrochloride surfactants derived from L-phenylalanine and
L-tyrosine as catalysts on the Diels-Alder reaction between cyclopentadiene and methyl acrylate was studied. Both
chain lengths (C -C14) and head groups of the surfactants were found to influence the yield and selectivity of the
8
Diels-Alder product. The C10 derivatives of both phenylalanine and tyrosine surfactants gave the highest yields
and selectivity. Phenylalanine ester hydrochlorides showed better catalytic activity than the tyrosine derivatives.
Adduct optimum yield was obtained at a concentration relating to their critical micelle concentration (CMC)
values. The Diels-Alder reaction was also found to be favored in acidic condition (pH 3) as well as in the presence
of lithium chloride (LiCl) as salting out agent.
KEY WORDS: Diels-Alder, Chiral catalysts, Phenylalanine, Tyrosine, Micelle, CMC
INTRODUCTION
The Diels-Alder reaction is one of the most important carbon-carbon bond forming reactions
and has been involved in key steps in the making of important intermediates that leads to the
synthesis of anti-cancer and anti-viral drugs such as Taxol and Tamiflu, respectively [1, 2].
Since then, Diels-Alder reactions have formed an important part of the synthetic repertoire of
making intermolecular and intramolecular cyclic compounds.
Different strategies of enhancing asymmetric Diels-Alder reactions have been reported [3,
4
]. With this view, the choice of catalyst to enhance the yield and selectivity of Diels-Alder
reactions has also been an important issue that needs to be addressed [5, 6]. Catalysts such as
Lewis acids [7, 8] have been known to enhance Diels-Alder reactions but their use has been
restricted since they decompose in the presence of a small amount of water and cannot be reused
[
9].
The use of surfactants in assisting a variety of organic reactions is highly promising for basic
and applied research [10, 11]. Micelle forming surfactants have been widely used as reaction
medium for many important organic reactions since micelles form organized assemblies that
affect the rates of chemical reactions and the position of chemical equilibrium [12, 13]. The use
of surfactants in micellar medium offers the possibilities for reaction control due to special
properties such as solubilization, pre-orientation, microviscosity, polarity and charge effects that
surfactants can confer [14]. These effects influence the organic reactions by affecting the yield,
regio and stereochemistry of the products.
The idea of micellization for the rate-enhancement of Diels-Alder reactions dates back to the
1
980s, where higher yields were obtained when using water as solvent compared to other non-
polar solvents [15-18]. Hence, surfactants offer the possibility for organic reactions to occur in
aqueous media, and from the viewpoint of green chemistry, water is safer, harmless and
environmentally benign [19].
However, there has been limited work on the use of chiral micellar media to catalyze Diels-
Alder reactions. Amino acids are useful synthons from the chiral pool that help to provide a cost
_
_________
*
Corresponding author. E-mail: p.caumul@uom.ac.mu
This work is licensed under the Creative Commons Attribution 4.0 International License

510
P. Caumul et al.
effective way of synthesizing surfactants as chiral catalysts. Optically active surfactants derived
from S-leucine and phenylalanine have been reported to be effective catalysts for the reaction
between nonyl acrylate and cyclopentadiene [20].
In continuation for the search of effective chiral micellar catalysts for Diels-Alder reactions,
a range of pre-synthesized ester hydrochloride surfactants derived from L-phenylalanine and L-
tyrosine [21] were used as novel chiral micellar-based catalysts for the reaction between methyl
acrylate and cyclopentadiene. The effect of chain length and head groups of the surfactants on
the reaction yields and selectivity were investigated. The reaction conditions such as
concentration of surfactants, temperature, time and solvent variation were also studied in view
of investigating the optimum conditions for which these surfactants can act as effective catalysts
for the Diels-Alder reaction.
EXPERIMENTAL
L-Phenylalanine was obtained from HiMedia Laboratories (India). L-Tyrosine, octan-1-ol,
decan-1-ol, dodecan-1ol, tetradecan-1-ol, dicyclopentadiene and thionyl chloride were
purchased from Sigma-Aldrich (USA). p-Toluene sulfonic acid (PTSA) was obtained from
Merck (Germany). Silica gel (60–120 Mesh) used for column chromatography was obtained
from Alpha Chemika (India). Cetyltrimethyl ammonium bromide (CTAB) was obtained from
BDH Laboratory Supplies (England). Sodium dodecyl sulfate was obtained from Loba Chemie
(
India).
1
13
H and C NMR spectra were recorded at 250 MHz and 62.9 MHz, respectively, on a
Bruker electro spin NMR spectrometer using CDCl , D O and DMSO-d as solvents. GC-MS
3
2
6
analysis was carried out on a Clarus 500 GC-Clarus 560S Mass Spectrometer using an SGE
BPX5 capillary column (30 m × 0.32 mm × 0.5 µm), helium gas as carrier with a flow rate of
o
o
1
.50 mL/min, injector temperature of 240 C, detector temperature of 270 C and oven
o
o
o
temperature program 100 C (hold for 2 min), ramp rate of 15 C/min to 280 C (hold for 15
min), flow rate 1.50 mL/min. The cycloadduct isomers were identified by matching their mass
spectra with those in the NIST library. The order of product retention time of the isomers was
determined from literature data [22].
General method for the Diels-Alder reaction
o
Cyclopentadiene was obtained by thermal cracking of dicyclopentadiene at 160 C.
Cyclopentadiene (0.32 mL, 3.80 mmol) and methyl acrylate (0.17 mL, 1.90 mmol) were added
to an aqueous solution of the surfactant and the reaction mixture was stirred at room temperature
for 72 hours. The mixture was extracted with diethylether (3 × 20 mL). The organic phase was
dried over anhydrous sodium sulfate, filtered and the excess solvent was removed under vacuo
to yield the crude Diels-Alder adduct which was purified by column chromatography using
hexane/ethyl acetate in a ratio of 2:1. The pure product was obtained in 95% yield and was
analyzed using GC/MS.
1
Methyl bicyclo [2.2.1] hept-5-ene-2-carboxylate. H NMR (CDCl
3
) δ (ppm): 1.23 (1H, m), 1.39
1
3
(
(
2H, m), 1.84 (1H, m), 2.90 (2H, m), 3.61 (3H, s), 5.90 (1H, m), 6.15-6.19 (1H, m). C NMR
CDCl ) δ (ppm): 32.1 (CH ), 45.4 (C-CO), 46.0 (CH-CO), 48.5 (CH ), 52.5 (CH), 54.3 (O-
), 135.2 (2C, C=C), 178.1 (C=O). m/z (EI) 151.1873 (M , 30%). Retention times: 4.48 min,
3
2
2
+
CH
3
exo-cycloadduct, 4.63 min, endo-cycloadduct [lit: 12.7 min, exo-cycloadduct; 12.9 min, endo-
cycloadduct] [23]. The endo/exo ratio was calculated based on the peak areas of the endo and
exo-cycloadduct in the chromatogram.
Bull. Chem. Soc. Ethiop. 2017, 31(3)

The use of optically active O-alkyl ester hydrochlorides of L-phenylalanine and L-tyrosine 511
RESULTS AND DISCUSSION
The Diels-Alder reaction between methyl acrylate and cyclopentadiene gives rise to a mixture of
exo (thermodynamic) and endo (kinetic) products (Figure 1) [23]. The reaction was initially
carried out in the presence of the commercially available surfactant cetyltrimethyl ammonium
bromide (CTAB) in water.
O
+
+
O
OCH
3
O
OCH
3
O
Endo
Exo
Figure 1. Diels-Alder reaction between methyl acrylate and cyclopentadiene.
The presence of CTAB afforded higher product yield compared to the reaction where no
catalyst was used. At the critical micelle concentration (CMC), which is the concentration at
which surfactant monomers cyclize to form micelles, an increase in product yield of up to 95%,
together with a lower endo-exo ratio were observed.
L-Phenylalanine and L-tyrosine O-alkyl ester hydrochloride surfactants of varying lengths
8
(C to C14) (Figure 2) which have been previously synthesized by our group were tested as
potential chiral micellar catalysts for the Diels-Alder reaction between methyl acrylate and
cyclopentadiene.
O
n 2n+1
OC H
+
Cl-
NH
3
R
n
8
10
12
14
R = H
R = OH
Phe 8
Tyr 8
Phe 10
Tyr 10
Phe 12
Tyr 12
Phe 14
Tyr 14
Figure 2. L-Phenylalanine and L-tyrosine ester hydrochloride surfactants.
The studies were carried out at the CMCs of the surfactants and the results are summarized
in Table 1 [21]. An increase in the yield of the Diels-Alder adduct was obtained as the chain
length of the ester hydrochlorides was increased from C to C for both the phenylalanine
8
10
(
Table 1, entries 3 and 7) and tyrosine (Table 1, entries 16 and 20) series. This may be due to the
increase in the hydrophobic character of the surfactant molecules which favors the interaction
with the reacting substrates. The maximum catalytic efficiency was obtained with an alkyl chain
length of C10 for both surfactants. However, a further increase in the chain length from C10 to
C14 resulted in a decrease in the yield (Table 1, entries 14, 15, 27, 28) (Figure 3). This can be
attributed to the coiling effect of the surfactant of higher chain lengths which can potentially
alter the orientation of the substrates resulting in reduced yields [24]. An increase in the
percentage of the endo adduct was observed with increasing chain length of phenylalanine alkyl
esters while for tyrosine, the percentage of the endo adduct decreases from C
8
to C10 and then
increases from C12 to C14
.
Bull. Chem. Soc. Ethiop. 2017, 31(3)

512
P. Caumul et al.
*
Table 1. Reactions between cyclopentadiene and methyl acrylate carried out at the surfactants’ CMC .
o
Entry Solvent
Surfactant
-
CTAB
Phe8
CMC* mM
Temp ( C) Time/h Yield (%) Endo: Exo
1
2
3
4
5
6
7
8
9
Water
Water
Water
Water
Water
Water
Water
Hexane
DCM
THF
20
20
20
20
20
0
20
20
20
20
40
70
100
20
20
20
20
20
0
20
20
20
20
40
70
100
20
20
72
72
72
4
18
95
87
18
38
0
98
36
0
63
61
27
18
72
64
53
10
29
15
70
30
0
85 : 15
82 : 18
75 : 25
91 : 9
90 : 10
-
80 : 20
69 : 31
-
73 : 27
86 : 14
89 : 11
83 : 17
81 : 19
89 : 11
86 : 14
86 : 14
81 : 19
85 : 15
80 : 20
71 : 29
-
1.00
3.96
0.69
0.69
0.69
0.69
0.69
0.69
0.69
0.69
0.69
0.69
0.154
0.180
1.94
0.180
0.283
0.283
0.283
0.283
0.283
0.283
0.283
0.283
0.283
0.0388
0.0138
Phe10
Phe10
Phe10
Phe10
Phe10
Phe10
Phe10
Phe10
Phe10
Phe10
Phe12
Phe14
Tyr8
Tyr10
Tyr10
Tyr10
Tyr10
Tyr10
Tyr10
Tyr10
Tyr10
Tyr10
Tyr10
Tyr12
Tyr14
24
72
72
72
72
72
72
72
72
72
72
72
4
24
72
72
72
72
72
72
72
72
72
72
1
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
Water
Water
Water
Water
Water
Water
Water
Water
Water
Water
Hexane
DCM
THF
50
40
35
0
77 : 23
91 : 9
92 : 8
-
Water
Water
Water
Water
Water
44
34
85 : 15
85 : 15
*
CMC was studied using conductivity measurements and has been previously published [21].
Figure 3. Effect of chain lengths of L-phenylalanine and L-tyrosine on reaction yields of the
Diels-Alder adduct.
Bull. Chem. Soc. Ethiop. 2017, 31(3)

The use of optically active O-alkyl ester hydrochlorides of L-phenylalanine and L-tyrosine 513
Figure 4. Effect of chain lengths of L-Phenylalanine and L-Tyrosine on reaction selectivity.
The yield of the Diels-Alder adduct was found to increase with the reaction time. At 72 h,
the cyclic adduct was obtained in 98 and 70% yield using the C10 derivatives of phenylalanine
and tyrosine ester hydrochlorides respectively (Table 1, entries 7 and 20). When the Diels-Alder
reaction was carried out for longer reaction times the endo:exo ratio was found to decrease. This
is in line with what has been reported in literature, whereby longer reaction times cause retro
reaction to occur readily, favoring the formation of the more thermodynamically stable exo
product [23].
o
The optimum yield was obtained when the reaction was carried at 20 C (Table 1, entries 3,
o
7
, 14, 15, 16, 20, 27, 28). Increasing the temperature of the reaction beyond 20 C resulted in a
change in the micellar structure of the catalyst which reduces the yield of the product and
favoring at the same time the formation of the kinetic endo product [25].
The formation of the Diels-Alder adduct was found to be dependent on the nature of solvent.
For both the tyrosine and phenylalanine hydrochloride surfactant series, increasing the polarity
of the solvent from hexane to THF and to water caused an increase in the yield of the reaction.
This is in line with what has been previously reported, where the use of aqueous media was
found to enhance Diels-Alder reaction [26]. Non-polar solvents reduced both the yield and the
selectivity (Table 1, entry 21) of the cycloadduct since reverse micelles are known to be formed
in these media [27, 28]. Surprisingly, when DCM was employed using either tyrosine or
phenylalanine hydrochloride the yield obtained was negligible (Table 1, entries 9 and 22). This
is maybe due to the fact that the structural orientation of both Phe-10 and Tyr-10 surfactants
under these conditions do not favourably interact with the reacting substrates. This is in line
with Sousa’s work who demonstrated how a variation of catalysts in DCM can affect the
reaction yield as a result of how they interact with the reacting substrate [29].
From Table 1, it can be deduced that in general phenylalanine ester hydrochloride
surfactants proved to be more of a potential chiral micellar catalyst than the tyrosine analogues
in terms of both the yield and endo/exo ratio. This may be explained by the different orientations
adopted at the micellar interface by the phenylalanine and tyrosine ester hydrochlorides. When
the reacting substrates are introduced in the aqueous micellar solutions, dienes and dienophiles
come in close proximity of the micellar structure causing them to bind within the micelles
enhancing the reactivity. Therefore, the rate of reaction of surfactant-assisted catalysis for Diels-
Alder reactions in water will depend on the nature of surfactant, overall influence of
Bull. Chem. Soc. Ethiop. 2017, 31(3)

514
P. Caumul et al.
hydrophobic effects, electrostatic interactions and the accompanying medium effects. In the case
of phenylalanine esters, the phenyl ring remained folded away from the aqueous medium within
the micellar core together with the hydrophobic tail allowing better π-π-stacking between the
aromatic ring and reacting substrates. In case of the tyrosine dodecyl ester hydrochloride, the
OH moiety in tyrosine pulled the aromatic ring towards the aqueous layer thus causing less π- π-
stacking (Figure 5) [30-32]. Figure 5 shows how the reacting substrates may interact with
phenylalanine and tyrosine dodecyl ester hydrochlorides which has led to the different yields
and endo/exo behaviors.
O
+
O
H
OCH3
NH
3
O
+
H N
3
C
Phenyl ring within
micellar core
H
O
O
H
H
O
C
OCH3
H
H
O
H
OCH3
H
H CO
3
O
endo
exo
Phenolic ring towards
aqueous layer
H
O
H
O
O
OCH3
C
+
O
H N
3
+
H
H N
3
H
O
O
H
O
O
C
OCH3
H
H
O
H
OCH
3
H
H CO
3
O
endo
exo
Figure 5. Postulate model showing the interactions between L-phenylalanine and L-tyrosine
catalysts with cyclopentadiene and methyl acrylate.
Bull. Chem. Soc. Ethiop. 2017, 31(3)

The use of optically active O-alkyl ester hydrochlorides of L-phenylalanine and L-tyrosine 515
After the successful acceleration of the Diels-Alder reactions with cationic surfactants, the
study was extended to explain how the yield and selectivity of the cyclo-adduct can be affected
using different concentrations of catalysts before, at and after the critical micelle concentration
of the catalyst. CTAB was initially used to study the effect of micellization on the yield and
selectivity of the Diels-Alder reaction (Figure 6). At a concentration of 0.02 mM of CTAB
which is well below its CMC, a low yield was observed. At the onset of the CMC of CTAB, an
abrupt increase in the yield of the Diels-Alder adduct was observed. The yield then decreases
upon further increase in concentration above the CMC of CTAB. Micellization was also found
to affect the selectivity of the Diels-Alder reaction, whereby an increase in the concentration of
CTAB to its CMC and above increased the ratio of the endo over the exo adduct.
Figure 6. Effect of varying the concentration of CTAB on yield and selectivity.
The effect of micellization was also studied with the tyrosine esters. The results are shown
in Table 2.
Table 2. Influence of CMC value on the yield and selectivity of the reaction between cyclopentadiene and
o
methyl acrylate-water, 72 h, 20 C.
Entry
Surfactant
Tyr10
Tyr10
Tyr10
Tyr12
Tyr12
Tyr14
Tyr14
Conditions
0.5×CMC
CMC
4×CMC
CMC
4×CMC
CMC
4×CMC
Yield (%)
Endo : Exo
83 :17
1
2
3
4
5
6
7
24
71
3
44
22
34
34
80 : 20
86 : 14
85 : 15
88 : 12
85 : 15
85 : 15
All the tyrosine esters showed similar trends as that observed with CTAB. When their
concentrations are below their respective CMC values, the surfactants exist in the monomeric
form. At the CMC, a steady increase in the yield of the Diels-Alder adduct was observed due to
the formation of micelles in the reaction medium, which helped in the solubilization and
orientation of the reactants within the micellar core, hence favouring the yield and selectivity of
the reaction. A further increase in the concentration above the CMC values resulted in greater
selectivity of the Diels-Alder adduct towards the endo product. This might be due to a change in
Bull. Chem. Soc. Ethiop. 2017, 31(3)

516
P. Caumul et al.
the shape of the micelles when the concentration of the surfactant is increased well above its
CMC [33] which favoured the kinetic endo product over the thermodynamic one. However, at
this particular concentration, a drop in the yield of the product was observed which might be
explained by the change in the micellar structure which rendered the reaction unfavorable.
The pH of the reaction medium has been known to play a vital role in the yield and
selectivity of the product [20, 34]. The effect of pH was investigated using CTAB and dodecyl
tyrosine ester hydrochloride in water (Table 3). The pH was adjusted by dropwise addition of 2
M HCl (pH < 3) or 2 M NaOH (pH > 3) and was monitored using a pH meter. At extreme acidic
conditions, pH 1, the cyclo-adduct was obtained in only 13% yield. This can be attributed to the
breakdown of self-aggregates of the micelles. Increasing the pH to 3 was found to enhance both
the yield and selectivity of the product (entry 2, Table 3). This is in line with previous studies
whereby it was reported that pH 3 provides favourable polarization of the acrylate molecule in
protic media stabilizing the micellar aggregates [20]. At higher pH, surfactants exist as the free
amine and can form hydrogen bonding with the acrylate which is no longer protonated, thus
stabilizing the reactive intermediates and hence favoring the reaction and also the preferential
formation of the thermodynamically stable exo isomer.
The effects of using a salting-out agent was also investigated. LiCl was added as a salting
out agent which helped remove the reactants from the aqueous pseudo-phase, increasing the
complexation of the substrate to the micelles. Moreover, increasing concentration of chloride
counter ions caused a shrinkage in the Stern layer (region in the micelle which contains the polar
head groups as well as counter ions tightly bound that interact with the aqueous exterior) which
lead to a greater pre-orientation thus forcing the reactants to come closer thus resulting in
enhanced yield (Table 3, entry 6). As expected, the reaction yield of the cycloadduct increased
to 84%. However, a large drop in the endo/exo ratio was observed showing that the production
of the exo isomer was favoured.
Table 3. Variation of pH and salting-out agent on the reaction between cyclopentadiene and methylacrylate-
o
water, 72 h, 20 C.
Entry
Surfactant
Tyr10
Tyr10
Tyr10
Tyr10
Tyr10
Tyr10
pH
1
3
5
7
Conditions
At CMC
At CMC
CMC
CMC
Yield (%)
Endo : Exo
83 : 17
93 : 7
78 : 22
80 : 20
79 : 21
80 : 20
1
2
3
4
5
6
13
77
56
71
68
84
9
3
CMC
At CMC + 4.86 M LiCl
CONCLUSION
We have demonstrated that our pre-synthesized surfactant compounds derived from L-tyrosine
and L-phenylalanine are promising chiral micellar catalysts for Diels-Alder reactions. We also
compared and carried out for the first time a comparative catalytic study of these amino acid
surfactants with cationic CTAB under varying conditions. The C10 derivatives for both
phenylalanine and tyrosine generated higher yields (up to 98%) and selectivities (high
endo/ratio up to 92%) of the Diels-Alder product. The ester hydrochloride surfactants showed
optimum activity when used at a concentration corresponding to their respective CMC values,
under an acidic condition (pH =3) as well as in the presence of LiCl as salting-out agent.
Bull. Chem. Soc. Ethiop. 2017, 31(3)

The use of optically active O-alkyl ester hydrochlorides of L-phenylalanine and L-tyrosine 517
ACKNOWLEDGEMENTS
We are grateful to the following technical staff at the University of Mauritius: Mrs.
S. L’Omelette-Moonien for the running of the NMR and Mr. Abdool Cader Dawoojee Wahed
for running the GC-MS.
REFERENCES
1
2
. Nicalaou, K.C.; Snyder, S.A.; Montagnon, T.; Vassilikogiamakis, G. The Diels-Alder
reaction in total synthesis. Angew. Chem. Int. Ed. 2002, 41, 1668-1698.
. Magano, J. Synthetic approaches to the Neuraminidase inhibitors Zanamivir (Relenza) and
Oseltamivir phosphate (Tamiflu) for the treatment of influenza. Chem. Rev. 2009, 109,
4
398-4438.
3
4
5
6
. Nishimoto, K.; Okada, Y.; Kim, S.; Chiba, K. Rate acceleration of Diels-Alder reactions
utilizing a fluorous micellar system in water. Electrochim. Acta 2011, 56, 10626-10631.
. Ghadari, R. In silico study to evaluate the governing criteria in the BF catalysed Diels-
3
Alder reaction. Comp. Theor. Chem. 2016, 1091, 176-185.
. Miller, J.P. Advances in Chemical Research, Nova Science Publications: New York; 2013;
pp. 179-219.
. Erfurt, K.; Wandzik, I.; Walczak, K.; Matuszek, K.; Chrobok, A. Hydrogen-bond-rich ionic
liquids as effective organocatalysts for Diels-Alder reaction. Green Chem. 2014, 16, 3508-
3
514.
. Marković, Z.; Predojevic, J.; Manojlovic, N.T. Synthesis of C
presence of tin(IV) chloride as a Lewis acid catalyst. Bull. Chem. Soc. Ethiop. 2011, 25, 83-
0.
. Mosaddegh, E.; Hassankhani, A. One-pot synthesis of polyhyropyridine derivatives via
Hantzsch four component condensation in water medium: use of a recyclable Lewis acid
7
8
7
-C16-alkyl maltosides in the
9
[
4 2 2
Ce(SO ) .4H O] catalyst. Bull. Chem. Soc. Ethiop. 2012, 26, 461-465.
9
1
. Kobayashi, S.; Manabe, K. Green Lewis acid catalysis in organic synthesis. Pure Appl.
Chem. 2000, 72, 1373-1380.
0. Kumar, B.; Tikariha, D.; Ghosh, K.K.; Barbero, N.; Quagliotto, P. Kinetic study on effect of
novel cationic dimeric surfactants for the cleavage of carboxylate ester ester. J. Phys. Org.
Chem. 2013, 26, 626-631.
1
1. Ghosh, K.K.; Kolay, S.; Bal, S.; Satnami, M.; Quagliotto, P. Effect of cationic gemini
surfactants on the hydrolysis of carboxylate and phosphate esters using hydroxamate ions.
Colloid. Polymer. Sci. 2008, 286, 293-303.
1
1
2. El Seoud, O.A. Effects of organized self assembly on acid-base equilibria. Adv. Colloid.
Interface Sci. 1989, 30, 1-30.
3. Bunton, C.A. Reactivity in aqueous association colloids: Descriptive utility of the
pseudophase model. J. Mol, Liq. 1997, 72, 231-249.
1
1
4. Tiascoglu, T. Micellar solutions as reaction media. Tetrahedron 1996, 52, 11113-11152.
5. Grieco, P.A.; Garner, P.; He, Z. Micellar catalysis in the aqueous intermolecular Diels-Alder
reaction: Rate acceleration and enhanced selectivity. Tetrahedron Lett. 1983, 24, 1897-1900.
6. Braun, R.; Schuster, F.; Sauer, J. (4+2)-Cycloadditionen in micellen: ein vergleich des
producktspektrums und der reaktionsgeschwindigkeit mit reaktionen in lösung. Tetrahedron
Lett. 1986, 27, 1285-1288.
7. Singh, V.K.; Raju, B.N.; Deota, P.T. Micellar catalysis π + π cycloaddition in aqueous
media. Synth. Comm. 1988, 18, 567-574.
8. Breslow, R.; Maitra, U.; Rideout, D.C. Selective Diels-Alder reactions in aqueous solutions
and suspensions, Tetrahedron Lett. 1983, 24, 1901-1904.
1
4
S
2S
1
1
1
9. Grieco, P.A, Garner, P.P.; Organic synthesis in water. London: Blacky Academic and
Professional: London; 1998; pp.1-46.
Bull. Chem. Soc. Ethiop. 2017, 31(3)

518
P. Caumul et al.
2
2
0. Diego-Castro, M.J.; Hailes, H.C. Novel application of chiral micellar media to the Diels-
Alder reaction. Chem. Commun. 1998, 15, 1549-1550.
1. Joondan, N.; Jhaumeer-Laulloo, S.; Caumul, P. A study of the antibacterial activity of L-
phenylalanine and L-tyrosine esters in relation to their CMCs and their interactions with 1,2-
dipalmitoyl-sn-glycero-3-phosphocholine, DPPC as model membrane. Microbiol. Res. 2014,
1
69, 675-685.
2
2
2
2
2. Cativiela, C.; Figueras, F.; Fraile, J.M.; Garcia, J.L.; Mayoral, J.A.; de Menorval, L.C.;
Pires, E. Heterogeneous Catalysis and Fine Chemicals III, Elsevier: Amsterdam; 1993.
3. Mukerjee, P. The nature of the association equilibria and hydrophobic bonding in aqueous
solutions of association colloids. Adv. Colloid Interface Sci. 1967, 1, 241-275.
4. Diego-Castro, M.J.; Hailes, H.C. Studies on the use of surfactants in aqueous Diels-Alder
reactions. Tetrahedron Lett. 1998, 39, 2211-2214.
5. Goto, A.; Takemoto, M.; Endo, F. A thermodynamic study on micellization of nonionic
surfactant in water and in water-ethanol mixture by gel filtration. Bull. Chem. Soc. Jpn.
1
985, 58, 247-251.
6. Woodward, R.B.; Baer, H. The reaction of furan with maleic anhydride. J. Am. Chem. Soc.
948, 70, 1161.
2
1
2
2
7. Attwood, D.; Florence, A.T. Surfactant Systems, Springer: Netherlands; 1983; pp.72-123.
8. Rossen, M.J.; Kunjappu, J.T. Surfactants and Interfacial Phenomena, Wiley: New Jersey;
2
012; pp.123-191.
2
3
3
3
9. Sousa, C.A.; Rodríguez-Borges, J.E.; Friere, C. New L-Serine derivative ligands as
cocatalysts for Diels-Alder reaction. Organic Chemistry 2013, 2013, Article ID 217675, 1-5.
DOI: http://dx.doi.org/10.1155/2013/217675.
0. Vijay, R.; Angayarkanny, S.; Baskar, G. Amphiphilic dodecyl ester derivatives from
aromatic amino acids: significance of chemical architecture in interfacial adsorption
characteristics. Colloids and Surfaces A: Physicochem. Eng. Aspects 2008, 317, 643-649.
1. Vijay, R.; Singh, J.; Baskar, G.; Ranganathan, R. Amphiphilic lauryl ester derivatives from
aromatic amino acids: significance of architecture in aqueous aggregation properties. J.
Phys. Chem. B. 2009, 113, 13959-13970.
1
2. Vijay, R.; Mandal, A.B.; Baskar, G. H NMR spectroscopic investigations on the
conformation of amphiphilic aromatic amino acid derivatives in solution: effect of chemical
architecture of amphiphiles and polarity of solvent medium. J. Phys. Chem. B. 2010, 114,
1
3691-13702.
3
3
3. Aswal, V.K.; Goyal, P.S.; Thiyagarajan, P. Small-angle neutron-scattering and viscosity
studies of CTAB/NaSaI viscoelastic micellar solutions. J. Phys. Chem. B. 1998, 102, 2469-
2
473.
4. Mubofu, E.B.; Engberts, J.B.F.N. Surfactant-assisted specific acid catalysis of Diels-Alder
reactions in aqueous media. J. Phys. Org. Chem. 2007, 20, 764-770.
Bull. Chem. Soc. Ethiop. 2017, 31(3)