LiClO4-accelerated three-component Mannich-type reaction of diethyl malonate with imines: An efficient synthesis of β-amino esters under solvent-free conditions

Article abstract of DOI:10.1080/00397910802271297

LiClO4 is used as catalyst for direct Mannich-type reaction of aryl aldehydes, aryl amines, and diethyl malonic ester under solvent-free conditions. This three-component reaction afforded the corresponding β-amino esters in good yields with simple and env

Full text of DOI:10.1080/00397910802271297

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LiClO4-Accelerated Three-
Component Mannich-Type
Reaction of Diethyl Malonate
with Imines: An Efficient
Synthesis of β-Amino Esters
Under Solvent-Free Conditions
Fezzeh Aryanasab a & Mohammad R. Saidi a
a Department of Chemistry, Sharif University of
Technology, Tehran, Iran
Published online: 20 Oct 2008.
To cite this article: Fezzeh Aryanasab & Mohammad R. Saidi (2008) LiClO4-
Accelerated Three-Component Mannich-Type Reaction of Diethyl Malonate with
Imines: An Efficient Synthesis of β-Amino Esters Under Solvent-Free Conditions,
Synthetic Communications: An International Journal for Rapid Communication of
Synthetic Organic Chemistry, 38:22, 4036-4044, DOI: 10.1080/00397910802271297
To link to this article: http://dx.doi.org/10.1080/00397910802271297
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Synthetic Communications1, 38: 4036–4044, 2008
Copyright # Taylor & Francis Group, LLC
ISSN: 0039-7911 print=1532-2432 online
DOI: 10.1080/00397910802271297
LiClO4-Accelerated Three-Component Mannich-
Type Reaction of Diethyl Malonate with Imines:
An Efficient Synthesis of b-Amino Esters Under
Solvent-Free Conditions
Fezzeh Aryanasab and Mohammad R. Saidi
Department of Chemistry, Sharif University of Technology, Tehran, Iran
Abstract: LiClO4 is used as catalyst for direct Mannich-type reaction of aryl alde-
hydes, aryl amines, and diethyl malonic ester under solvent-free conditions. This
three-component reaction afforded the corresponding b-amino esters in good
yields with simple and environmentally benign procedure.
Keywords: b-Amino esters, diethyl malonate, imines, lithium perchlorate,
Mannich type, solvent free
b-Amino carbonyl compounds are important synthetic tools in organic
chemistry and are valuable starting materials for the preparation of a
large number of pharmaceuticals and natural products. They are also
useful as the immediate precursors for the synthesis of b-lactams and
b-amino acids.[1] Therefore much attention has been focused on the effi-
cient synthesis of these compounds. Among the synthetic methods
reported in the literature, nucleophilic additions to the C¼N bond of
imines, especially three-component Mannich reactions, are of paramount
importance in the synthesis of amino derivatives.
The Mannich-type reaction is a very important carbon–carbon bond-
forming reaction in organic synthesis,[2] and one of the most widely uti-
lized chemical transformations for constructing the b-amino carbonyl
compounds.[3–14] A more desirable version of the Mannich reaction
Received April 26, 2008.
Address correspondence to Mohammad R. Saidi, Department of Chemistry,
Sharif University of Technology, Tehran, Iran. E-mail: saidi@sharif.edu
4036

Reaction of Diethyl Malonate with Imines
4037
involves the use of a one-pot, three-component strategy that allows
preparation of a wide range of structural variations.[15–22]
Furthermore, only a few one-pot procedures on the use of unmodi-
fied carbonyl compounds have been reported in the literature. Also, a
variety of catalysts such as NbCl5,[23] Zn(OTf)2,[24,25] Bi(OTf)3 ꢀ 4H2O,[26]
H3PW12O40,[27]
ZrOCl2 ꢀ 8H2O,[28]
dodecylbenzenesulfonic
acid
(DBSA),[29] sodium dodecyl sulfate (SDS)–HCl,[30–32] PS–SO3H,[33]
L-proline,[12] and sodium tetrakis(3,5-trifluoromethylphenyl)-borate[34]
have been used for this reaction. However, these methods have some
drawbacks such as long reaction time, use of costly and unrecoverable
catalysts, use of toxic reagents, and special effort for catalyst preparation.
LiClO4 has emerged as a powerful promoter in many chemical pro-
cesses and in different organic media.[35–42] In the present report, we have
found that LiClO4 is an efficient catalyst for the synthesis of b-amino
carbonyl compounds through a one-pot, three-component reaction
of aldehydes, amines, and diethyl malonic ester under solvent-free
conditions at room temperature.
Initially, the three-component Mannich reaction of p-bromobenz-
aldehyde, 1a (1 mmol), aniline 2a (1 mmol), and diethyl malonic ester
(1.5 mmol) was examined. To optimize the reaction conditions, different
solvents and solvent-free conditions were screened in the model reaction.
The results showed that yields of the desired products in solvent-free con-
ditions are higher than other conditions (Table 1). Furthermore, when
the starting materials were treated in the presence of solid lithium per-
chlorate, it was found that the optimum amount of catalyst is 50 mol%
(Table 1, Scheme 1).
Table 1. Three-component reaction of 1a, 2a, and diethyl malonate under
different conditions
Entry
Solvent
LiClO4 (mmol)
Yield (%)a
1
2
3
4
5
6
7
8
9
MeOH
CH3CN
H2O
CH2C12
CH2C12
Solvent free
Solvent free
Solvent free
Solvent free
0.5
0.5
0.5
0.5
0
0.5
0.125
0.25
1
45
50
nrb
70
20
98
30
45
95
aConversion yields.
bNo reaction.

4038
F. Aryanasab and M. R. Saidi
Scheme 1. Mannich reaction of 4-bromobenzaldehyde with aniline and diethyl
malonate.
With optimized reaction conditions in hand, the scope of the reaction
was explored with different starting materials, and several analogs of
compound 3 were synthesized in good to excellent yields (Table 2,
Table 2. Three-component Mannich reaction of aromatic amines, aromatic
aldehyde, and diethyl malonate
Entry
R
R1
Products
Yield (%)a
4=5b
Ref.
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
p-Br
p-Br
m-NO2
p-Cl
m-NO2
p-Cl
H
m-NO2
H
m-NO2
p-OMe
H
p-Cl
p-NO2
H
H
H
p-OMe
H
3a, 4a
3b, 4a
3c, 4c
3d, 4d
3e, 4c
3f, 4d
3g, 4g
3h, 4c
3i, 4g
3j, 4c
98
100
98
100
97
96
85
85
80
70
63
60
55
98
98
94
95
0
95=5
80=20
98=2
80=20
98=2
95=5
90=10
76=24
70=30
95=5
100=0
95=5
96=4
47=58
42=58
9=9
25
24
25
25
42
25
25
25
24
24
43
24
25
24
44
44
44
3,4-di Cl
p-Cl
3,4-di Cl
H
p-Cl
H
p-OMe
3,4-di Cl
p-NO2
H
p-NO2
p-NO2
p-OH
p-Cl
3k, 4k
3l, 4g
3m, 4d
3n, 4n
3o, 4g
3p, 4g
3q, 4g
3r, 4k
p-OMe
p-OH
p-OH
5=95
0=0
aConversion yields.
1
bCalculated by the H NMR spectrum.

Reaction of Diethyl Malonate with Imines
4039
Scheme 2. Three-component Mannich reaction with diethyl malonate.
Scheme 2). As can be seen from Table 2, higher ratio of 3=4 was obtained
with amines containing electron-withdrawing groups (Table 2, entries
10, 12, and 13). By using amines containing strong electron-donating
groups, a lower ratio of 3=4 was obtained because of their electron-rich
carbon–nitrogen double bonds (Table 2, entries 16 and 17). When
p-hydroxybenzaldehyde was reacted with p-methoxyaniline under the
optimum conditions, the desired product was not formed (Table 2, entry
18). However, the electron-rich amines gave good yields of diethyl benzyl-
idenemalonate derivatives 4 (Table 2, entries 16 and 17).
In summary, we have developed a versatile method for the synthesis
of b-amino esters using solid LiClO4 as a catalyst in a Mannich-type
reaction of diethyl malonate with imines, which are generated in situ
from the corresponding aromatic amines and aromatic aldehydes. This
protocol is facile and efficient for the aromatic amines and aromatic
aldehydes.
EXPERIMENTAL
Typical Procedure: The Synthesis of 4c
A
mixture of 3-chlorophenylamine (1 mmol), 3-nitrobenzaldehyde
(1 mmol), diethyl malonic ester (1.2 mmol), and LiClO4 (0.5 mmol) was
stirred at room temperature for 5 h. Ethyl acetate (10 mL) was added,
and the solid LiClO4 was filtered off. The filtrate was washed with water
(2 ꢁ 10 mL), dried with sodium sulfate, and filtered. After removing the
solvent under reduced pressure, the residue was purified by flash column
chromatography on silica gel using ethyl acetate–hexane (1:3) to afford
pure 4c as a yellow solid. All of the products are known, and the struc-
1
tures of the products were determined from their H NMR, 13C NMR,
and IR spectra and by comparison with those reported in the literature.

4040
F. Aryanasab and M. R. Saidi
Caution: The use of dry lithium perchlorate as catalyst is safe, but it is
advisable to dry LiClO4 in a fume hood using a lab-shield.
Selected Spectroscopic Data
Compound 4b
1H NMR (500 MHz, CDCl3): d 7.41 (d, 2H), 7.21 (d, 2H), 7.05 (d, 1H),
6.64 (s, 1H), 6.35 (d, 1H), 5.65 (br, 1H), 5.05 (d, 1H), 4.17–4.10 (m, 4H),
3.78 (d, 1H), 1.17 (t, 3H), 1.14 (t, 3H). 13C NMR (125 MHz, CDCl3): d
167.9, 166.8, 146.3, 138.4, 133.2, 132.3, 132.2, 131.2, 130.9, 128.8,
122.3, 121.1, 115.3, 113.4, 62.2, 61.9, 57.8, 56.8, 14.4, 14.3 ppm.
Compound 4c
1H NMR (500 MHz, CDCl3): d 8.21 (s, 1H), 8.00–7.95 (m, 1H), 7.65 (t,
1H), 7.38 (t, 1H), 6.95–6.84 (d, 2H), 6.45–6.37 (d, 2H), 5.56 (dd,
J ¼ 5.4, 9.0 Hz, 1H), 5.18 (d, J ¼ 9.0 Hz, 1H), 4.06–4.95 (m, 4H), 3.85
(d, J ¼ 5.4 Hz, 1H), 1.11 (t, J ¼ 7.1 Hz, 3H), 1.02 (t, J ¼ 7.1 Hz, 3H).
13C NMR (125 MHz, CDCl3): d 167.9, 166.8, 148.8, 148.3, 142.1,
135.3, 133.3, 131.1, 130.9, 128.8, 122.2, 121.1, 115.3, 113.4, 62.2, 61.9,
57.8, 56.8, 14.4, 14.3 ppm.
Compound 3f
1H NMR (500 MHz, CDCl3): d 7.25–7.20 (m, 4H), 6.92 (d, 2H), 6.45 (d,
2H), 5.5 (br, 1H), 5.1 (d, 1H), 4.17–4.10 (m, 4H), 3.75 (d, 1H), 1.17 (t,
3H), 1.13 (t, 3H). 13C NMR (125 MHz, CDCl3): d 168.3, 167.3, 144.7,
137.6, 133.7, 129.0, 128.9, 128.1, 122.9, 114.9, 62.2, 61.9, 57.8, 56.8,
14.4, 14.3 ppm.
Compound 3g
1H NMR (500 MHz, CDCl3): d 7.25–7.22 (m, 2H), 7.21–7.18 (m, 2H),
7.13–7.08 (m, 1H), 6.97–6.89 (m, 2H), 6.52–6.50 (m, 1H), 6.44–6.42 (m,
2H), 5.61 (br, 1H), 5.29 (d, 1H), 4.32–4.15 (m, 4H), 3.83 (d, 1H), 1.25
(t, 3H), 1.17 (t, 3H). 13C NMR (125 MHz, CDCl3): d 167.5, 166.6,
147.7, 141.9, 129.3, 128.7, 127.7, 127.4, 117.9, 114.3, 62.2, 61.9, 56.3,
53.8, 14.1, 13.9 ppm.

Reaction of Diethyl Malonate with Imines
4041
Compound 4h
1H NMR (500 MHz, CDCl3): d 8.5 (s, 1H), 8.35 (m, 1H), 8.22 (m, 1H),
7.68 (m, 1H), 6.58 (d, 2H), 6.48 (d, 2H), 5.14 (d, 1H), 4.11–4.05 (m,
4H), 4.07 (d, 1H), 3.06 (s, 3H), 1.13 (t, 3H), 1.11 (t, 3H). 13C NMR
(125 MHz, CDCl3): d 167.6, 166.8, 153.1, 148.8, 143.2, 139, 135.2,
133.7, 129.6, 125.3, 122.9, 115.8, 115, 114.7, 62.2, 61.9, 58.1, 55.5, 54.6,
14.3, 14.1 ppm.
Compound 3o
1H NMR (500 MHz, CDCl3): d 7.43–7.35 (m, 5H), 7.15–7.12 (m, 2H),
6.63–6.60 (m, 2H), 5.37 (br, 1H), 5.12 (d, 1H), 4.21–4.37 (m, 4H), 3.85
(d, 1H), 1.35 (t, 3H), 1.23 (t, 3H).13C NMR (125 MHz, CDCl3): d 168.7,
167.8, 145.3, 139.3, 129.2, 129.0, 128.1, 126.8, 122.8, 115.2, 62.9, 62.3,
58.3, 57.8, 15.1, 14.9 ppm.
ACKNOWLEDGMENTS
We are grateful to the Sharif University of Technology Research Council
for financial support of this research.
REFERENCES
1. Arend, M.; Westermann, B.; Risch, N. Modern variants of the Mannich
reaction. Angew. Chem., Int. Ed. 1998, 37, 1044–1070.
2. Kobayashi, S.; Ishitani, H. Catalytic enantioselective addition to imines.
Chem. Rev. 1999, 99, 1069–1094.
3. Martin, S. F. Evolution of the vinylogous Mannich reaction as a key
construction for alkaloid synthesis. Acc. Chem. Res. 2002, 35, 895–904.
4. Joshi, N. S.; Whitaker, L. R.; Francis, M. B. A three-component Mannich-
type reaction for selective tyrosine bioconjugation. J. Am. Chem. Soc. 2004,
126, 15942–15943.
5. Zhuang, W.; Sabby, S.; Jorgensen, K. A. Direct organocatalytic enantioselec-
tive Mannich reactions of ketimines: An approach to optically active quatern-
ary a-amino acid derivatives. Angew. Chem, Int. Ed. 2004, 43, 4476–4478.
´
6. Cordova, A. The direct catalytic asymmetric Mannich reaction. Acc. Chem.
Res. 2004, 37, 102–112.
7. Notz, W.; Tanaka, F.; Watanabe, S.-I.; Chowdari, N. S.; Turner, J. M.;
Thayumanavan, R.; Barbas, C. F. The direct organocatalytic asymmetric
Mannich reaction: Unmodified aldehydes as nucleophiles. J. Org. Chem.
2003, 68, 9624–9634.

4042
F. Aryanasab and M. R. Saidi
8. Matsunaga, S.; Kumagai, N.; Harada, S.; Shibasaki, M. anti-Selective direct
catalytic asymmetric Mannich-type reaction of hydroxyketone providing
b-amino alcohols. J. Am. Chem. Soc. 2003, 125, 4712–4713.
9. Juhl, K.; Gathergood, N.; Jørgensen, K. A. Catalytic asymmetric direct
Mannich reactions of carbonyl compounds with a-imino esters. Angew.
Chem., Int. Ed. 2001, 40, 2995–2997.
10. List, B. The direct catalytic asymmetric three-component Mannich reaction.
J. Am. Chem. Soc. 2000, 122, 9336–9337.
11. Kobayashi, S.; Hamada, T.; Manabe, K. The catalytic asymmetric Mannich-
type reactions in aqueous media. J. Am. Chem. Soc. 2002, 124, 5640–5641.
12. Hayashi, Y.; Tsuboi, W.; Ashimine, I.; Urushima, T.; Shoji, M.; Sakai, K.
The direct and enantioselective, one-pot, three-component, cross-Mannich
reaction of aldehydes. Angew. Chem., Int. Ed. 2003, 42, 3677–3680.
13. Maheswara, M.; Siddaiah, V.; Rao, Y. K.; Tzeng, Y.-M.; Sridhar, C. A sim-
ple and efficient one-pot synthesis of 1,4-dihydropyridines using heteroge-
neous catalyst under solvent-free conditions. J. Mol. Catal. A: Chem. 2006,
260, 179–180.
14. Narasimhulu, M.; Reddy, T. S.; Mahesh, K. C.; Prabhkar, P.; Rao, C. B.;
Venkateswarlu, Y. Silica supported perchloric acid: A mild and highly effi-
cient heterogeneous catalyst for the synthesis of poly-substituted quinolines
via Friedla¨nder hetero-annulation. J. Mol. Catal. A: Chem. 2007, 266,
114–117.
15. Josephsohn, N. S.; Snapper, M. L.; Hoveyda, A. H. Ag-catalyzed asymmetric
Mannich reactions of enol ethers with aryl, alkyl, alkenyl, and alkynyl imines.
J. Am. Chem. Soc. 2004, 126, 3734–3735.
16. Lou, S.; Taoka, B. M.; Ting, A.; Schaus, S. E. Asymmetric Mannich reac-
tions of b-keto esters with acyl imines catalyzed by cinchona alkaloids.
J. Am. Chem. Soc. 2005, 127, 11256–11257.
17. Ollevier, T.; Nadeau, E. Bismuth triflate–catalyzed three-component
Mannich-type reaction. J. Org. Chem. 2004, 69, 9292–9295.
18. Xu, L.-W.; Xia, C.-G.; Li, L. Transition metal salt-catalyzed direct three-
component Mannich reactions of aldehydes, ketones, and carbamates:
Efficient synthesis of N-protected b-aryl-b-amino ketone compounds.
J. Org. Chem. 2004, 69, 8482–8484.
19. Hamada, T.; Manabe, K.; Kobayashi, S. Enantio- and diastereoselective,
stereospecific Mannich-type reactions in water. J. Am. Chem. Soc. 2004,
126, 7768–7769.
20. Loh, T.-P.; Chen, S.-L. InCl3-catalyzed three-component asymmetric
Mannich-type reaction in methanol. Org. Lett. 2002, 4, 3647–3650.
21. Chowdari, N. S.; Suri, J. T.; Barbas, C. F. Asymmetric synthesis of quatern-
ary a- and b-amino acids and b-lactams via proline-catalyzed Mannich reac-
tions with branched aldehyde donors. Org. Lett. 2004, 6, 2507–2510.
22. Josephsohn, N. S.; Carswell, E. L.; Snapper, M. L.; Hoveyda, A. H. Practical
and highly enantioselective synthesis of b-alkynyl-b-amino esters through
Ag-catalyzed asymmetric Mannich reactions of silylketene acetals and alky-
nyl imines.Org. Lett. 2005, 7, 2711–2713.

Reaction of Diethyl Malonate with Imines
4043
23. Wang, R.; Li, B.; Huang, T.; Shi, L.; Lu, X. NbCl5-catalyzed one-pot
Mannich-type reaction: Three component synthesis of b-amino carbonyl
compounds. Tetrahedron Lett. 2007, 48, 2071–2073.
24. Wang, Y. G.; Yang, Y. Y.; Shou, W. G. Synthesis of b-amino carbonyl com-
pounds via a Zn(OTf)2-catalyzed cascade reaction of anilines with aromatic
aldehydes and carbonyl compounds. Tetrahedron 2006, 62, 10079–10086.
25. Wang, Y. G.; Yang, Y. Y.; Shou, W. G. An efficient synthesis of b-amino
esters via Zn(OTf)2-catalyzed Mannich-type reaction. Tetrahedron Lett.
2006, 47, 1845–1847.
26. Ollevier, T.; Nadeau, E.; Guay-Begin, A. A. Direct-type catalytic three-
component Mannich reaction in aqueous media. Tetrahedron Lett. 2006,
47, 8351–8354.
27. Azizi, N.; Torkiyan, L.; Saidi, M. R. Highly efficient one-pot three-
component Mannich reaction in water catalyzed by heteropoly acids. Org.
Lett. 2006, 8, 2079–2082.
28. Eftekhari-Sis, B.; Abdollahifa, A.; Hashemi, M. M.; Zirak, M. Stereoselective
synthesis of b-amino ketones via direct Mannich-type reactions, catalyzed
with ZrOCl2 ꢀ 8H2O under solvent-free conditions. Eur. J. Org. Chem. 2006,
5152–5157.
29. Manabe, K.; Kobayashi, S. Mannich-type reactions of aldehydes, amines,
and ketones in a colloidal dispersion system created by a brønsted acid–
surfactant-combined catalyst in water. Org. Lett. 1999, 1, 1965–1967.
30. Akiyama, T.; Matsuda, K.; Fuchibe, K. HCl-catalyzed stereoselective
Mannich reaction in H2O-SDS system. Synlett 2005, 322–324.
31. Manabe, K.; Mori, Y.; Kobayashi, S. Three-component carbon–carbon
bond-forming reactions catalyzed by a Brønsted acid–surfactant-combined
catalyst in water. Tetrahedron 2001, 57, 2537–2544.
32. Akiyama, T.; Takaya, J.; Kagoshima, H. HBF4 catalyzed Mannich-type
reaction in aqueous media. Synlett 1999, 1045–1048.
33. Iimura, S.; Nobutou, D.; Manabe, K.; Kobayashi, S. Mannich-type reactions
in water using a hydrophobic polymer-supported sulfonic acid catalyst.
Chem. Commun. 2003, 1644–1645.
34. Chang, C. T.; Liao, B. S.; Liu, S. T. Mannich-type reactions in a colloidal
solution formed by sodium tetrakis(3,5-trifluoromethylphenyl)borate as a
catalyst in water. Tetrahedron Lett. 2006, 47, 9257–9259.
35. Saidi, M. R.; Azizi, N. Synlett 2002, 1347–1349.
36. Saidi, M. R.; Azizi, N.; Zali-Boinee, H. A simple one-pot three-component
reaction for preparation of secondary amines and amino esters mediated by
lithium perchlorate. Tetrahedron 2001, 57, 6829–6832.
37. Saidi, M. R.; Azizi, N.; Naimi-Jamal, M. R. Lithium perchlorate assisted
one-pot three-component aminoalkylation of electron-rich aromatic com-
pounds. Tetrahedron Lett. 2001, 42, 8111–8113.
38. Saidi, M. R.; Azizi, N. A new protocol for the one-pot preparation of highly
diastereomerically enriched secondary amines and b-amino esters mediated
by lithium perchlorate solution in diethyl ether. Tetrahedron: Asymmetry
2002, 13, 2523–2527.

4044
F. Aryanasab and M. R. Saidi
39. Saidi, M. R.; Azizi, N. Highly diastereoselective aminoalkylation of
naphthols with chiral amines mediated by lithium perchlorate solution in
diethyl ether. Tetrahedron: Asymmetry 2003, 14, 389–392.
40. Azizi, N.; Rajabi, F.; Saidi, M. R. A mild and highly efficient protocol for
one-pot synthesis of primary a-amino phosphonates under solvent-free con-
ditions. Tetrahedron Lett. 2004, 45, 9233–9236.
41. Saidi, M. R.; Rajabi, F.; Brown, R. S. Enantioselective conjugate addition to
a,b-unsaturated esters and amides mediated by lithium perchlorate. J. Iranian
Chem. Soc., 2005, 2, 300–304.
42. Heydari, A. Organic synthesis in an unconventional solvent, 5.0 M lithium
perchlorate=diethyl ether. Tetrahedron 2002, 58, 6777–6793.
43. Wu, M.; Jing, H.; Chang, T. Synthesis of b-amino carbonyl compounds via
a Mannich reaction catalyzed by SalenZn complex. Catalysis Commun.
2007, 8, 2216–2220.
44. Harjani, J. R.; Nara, S. J.; Salunkhe, M. M. Lewis acidic ionic liquids for the
synthesis of electrophilic alkenes via the Knoevenagel condensation. Tetrahe-
dron Lett. 2002, 43, 1127–1130.