The reaction of dialkyl acetylenedicarboxylates with 2-oxo-2- phenylacetaldehyde in the presence of primary amines: Synthesis of alkyl 2-benzoyl-4-alkylamino-5-oxo-2,5-dihydro-3-furan carboxylate derivatives

Article abstract of DOI:10.3906/kim-1109-40

A 3-component domino reaction approach between a primary amine, a dialkyl acetylenedicarboxylate, and 2-oxo-2-phenylacetaldehyde that affords novel alkyl 2-benzoyl-4-alkylamino-5-oxo-2,5-dihydro-3-furan carboxylate derivatives is reported. The reaction se

Full text of DOI:10.3906/kim-1109-40

Turk J Chem
36 (2012) , 485 – 492.
¨
˙
c
ꢀ TUBITAK
doi:10.3906/kim-1109-40
The reaction of dialkyl acetylenedicarboxylates with
2-oxo-2-phenylacetaldehyde in the presence of primary
amines: synthesis of alkyl
2-benzoyl-4-alkylamino-5-oxo-2,5-dihydro-3-furan
carboxylate derivatives
Javad SAFAEI-GHOMI1, Fariba SALIMI1, Ali RAMAZANI2,∗
,
Fatemeh ZEINALI NASRABADI2 and Yavar AHMADI3
1Department of Organic Chemistry, Faculty of Chemistry, University of Kashan,
51167 Kashan-IRAN
e-mail: safaei@kashanu.ac.ir
2Department of Chemistry, University of Zanjan, P O Box 45195-313, Zanjan-IRAN
e-mail: aliramazani@gmail.com
3Young Researchers Club, Zanjan Branch, Islamic Azad University, Zanjan-IRAN
Received: 24.09.2011
A 3-component domino reaction approach between a primary amine, a dialkyl acetylenedicarboxy-
late, and 2-oxo-2-phenylacetaldehyde that affords novel alkyl 2-benzoyl-4-alkylamino-5-oxo-2,5-dihydro-3-
furan carboxylate derivatives is reported. The reaction sequence consists of an initial Michael addition
of primary amines to dialkyl acetylenedicarboxylates, followed by an aldol-like reaction with 2-oxo-2-
phenylacetaldehyde, and then γ -lactonization to afford the products. This cascade reaction sequence repre-
sents a rapid and unprecedented route to the described biologically interesting molecules.
Key Words: Dialkyl acetylenedicarboxylates, 2-oxo-2-phenylacetaldehyde, primary amines, furan, Michael
addition
Introduction
Multicomponent reactions (MCRs) allow more than 2 simple and flexible building blocks to be combined
in practical, timesaving 1-pot operations. Due to their valued features such as atom economy, inherent
∗Corresponding author
485

The reaction of dialkyl acetylenedicarboxylates with..., J. SAFAEI-GHOMI, et al.
simple experimental procedures, and their 1-pot character, they are perfectly suited for automated synthesis.1
Therefore, MCRs have attracted much attention because of their exceptional synthetic efficiency. 2−5 Since
all the organic reagents employed are used and moved toward the target compound, purification of products
resulting from MCRs is simple.6,7 Isocyanide-based multicomponent reactions (abbreviated to IMCRs by Ugi
and Do¨mling) have an advantageous position. The special features of IMCRs include unique synthetic potential,
high atom economy, convergent nature, ease of implementation, and the generation of molecular diversity.6−12
For years, acetylenic esters have attracted the attention of organic chemists, mostly as Michael accep-
tors.7,13,14 Recently, there has been increasing interest in the applications of acetylenic esters in multicomponent
syntheses1,7 especially for preparing stabilized phosphonium ylides.15−17 Due to the atom economy, convergent
character, and simplicity of 1-pot procedures, multicomponent condensation reactions have great potential in
synthesis. The development of novel multicomponent condensation reactions is also receiving growing interest
from industrial chemistry research groups, and represents a challenge for organic chemists.1,7
Furans, benzofurans, and their reduced forms are important core structures in many biologically active
natural products. Moreover, they are useful building blocks in the total synthesis of natural products and
pharmaceuticals.18−21 Many naturally occurring furans have exhibited considerable biological activities, such
as antitumor and cytotoxic properties22,23 as well as antimicrobial,24,25 antispasmodic,26 and several other
potentially useful activities.27 In addition, furans are also present in commercially important products, such
as agrochemical bioregulators, essential oils, cosmetics, dyes, photosensitizers, and flavoring and fragrance
compounds.27−29 As part of our ongoing program to develop efficient and robust methods for the preparation of
heterocyclic compounds,30,31 we sought to develop a convenient way to prepare alkyl 2-benzoyl-4-alkylamino-5-
oxo-2,5-dihydro-3-furan carboxylate derivatives 4a-j. Herein we report a hitherto unknown, 1-pot, 3-component
reaction, which, starting from readily available 2-oxo-2-phenylacetaldehyde 3, affords 4a-j (Scheme 1).
O
CO2R2
O
CH2Cl2
O
H
R1NH2
O
+
+
r. t., 24 h
O
R2O2C
CO2R2
R1
N
1
H
2
3
4
4a: R1 =4-methoxybenzyl, R2 =CH3 ; 4b: R1 =2-methoxybenzyl, R2 =CH3 ; 4c: R1 =4-methoxybenzyl,
R2 =CH3 CH2 ; 4d: R1 =4-methylbenzyl, R2 =CH3 ; 4e: R1 =4-methylbenzyl, R2 =CH3 CH2 ; 4f: R1 =benzyl,
R2 =CH3 ; 4g: R1 =benzyl, R2 =CH3 CH2 ; 4h: R1 =4-fluorobenzyl, R2 =CH3 ; 4i: R1 =4-fluorobenzyl,
R2 =CH3 CH2 ; 4j: R1 =propyl, R2 =CH3
Scheme 1. Three-component synthesis of alkyl 2-benzoyl-4-alkylamino-5-oxo-2,5-dihydro-3-furan carboxylate deriva-
tives 4 (see Experimental part).
Experimental
The starting materials and solvents were obtained from Merck (Germany) and Fluka (Switzerland) and were used
without further purification. The methods used to follow the reactions were TLC and NMR, which indicated
486

The reaction of dialkyl acetylenedicarboxylates with..., J. SAFAEI-GHOMI, et al.
that there was no side product. Melting points were measured on an Electrothermal 9100 apparatus and are
uncorrected. IR spectra were measured on a Jasco 6300 FTIR spectrometer. 1 H- and 13 C-NMR spectra were
measured (CDCl3) with a BRUKER DRX-250 AVANCE spectrometer at 250.0 and 62.5 MHz, respectively.
Elemental analyses were performed using a Heraeus CHN-O-Rapid analyzer. Mass spectra were recorded on a
FINNIGAN-MAT 8430 mass spectrometer operating at an ionization potential of 70 eV. Flash chromatography
columns were prepared with Merck silica gel (F254) powder.
General procedure for the preparation of compound 4a
To a magnetically stirred solution of 4-methoxybenzyl amine (1 mmol, 0.137g) was added dimethyl acetylenedi-
carboxylate (1 mmol, 0.142 g) in CH2 Cl2 (7 mL). The mixture was stirred for 1 h. Then oxo-2-phenylacetaldehyde
3 (1 mmol, 0.134g) was added, and the mixture was stirred for 24 h. The solvent was removed under reduced
pressure and the viscous residue was purified by flash column chromatography (silica gel (F254); petroleum
ether–AcOEt (10:2). The solvent was removed under reduced pressure and the products were obtained. The
characterization data of the compounds are given below.
Methyl 2-benzoyl-4-[(4-methoxybenzyl)amino]-5-oxo-2,5-dihydro-3-furancar- boxy-
late (4a)
Yellow oil, yield: 346 mg (91%). IR (KBr): 3350 (NH), 3000, 1770, 1700, 1670, 1600, 1475, 1150 cm−1 1 H-
;
NMR δ 6.86-8.06 (m, 9H, arom), 6.32 (s, 1H, CH), 4.82-4.98 (m, 2H, CH2), 3.60 and 3.80 (2s, 6H, 2OCH3),
2.17 (s, 1H, NH exchangeable by D2 O). 13 C-NMR δ 192.3, 169.1, 167.5 (3C=O), 159.1, 137.6, 130.4 (3C
arom), 134.1, 129.3, 129.1, 129.0, 128.8 (9CH arom), 135.1, 114.2 (2C, alkene), 76.2 (CH), 55.3, 51.3 (2MeO),
46.0 (CH2). Ms m/z (%) 381 (M+ , 14), 276 (19), 136 (29), 121 (89), 105 (100), 77 (53). Anal. Calcd. for
C21 H19 NO6 (381.38): C 66.13, H 5.02, N 3.67. Found: C 66.18, H 5.06, N 3.63.
Methyl 2-benzoyl-4-[(2-methoxybenzyl)amino]-5-oxo-2,5-dihydro-3-furancar- boxy-
late (4b)
Yellow oil, yield: 361 mg (95%). IR (KBr): 3400 (NH), 3050, 3000, 1770, 1700, 1670, 1600, 1475, 1120 cm−1
;
1 H-NMR δ 6.91-8.05 (m, 9H, arom), 6.27 (s, 1H, CH), 4.96-5.04 (m, 2H, CH2), 3.59, 3.89 (2s, 6H, 2MeO), 2.19
(s, 1H, NH). 13 C-NMR δ 192.4, 169.1, 164.3, (3C=O), 157.7, 136.8, 129.6 (3C arom), 135.2, 110.4 (2C alkene),
134.1, 129.2, 129.1, 129.0, 128.8, 126.57, 120.6 (9CH arom), 76.2 (CH), 55.3, 51.2 (2MeO), 42.2 (CH2). Ms m/z
(%) 381 (M+ , 2), 105 (100), 135 (50), 121 (87), 77 (91). Anal. Calcd. for C21 H19 NO6 (381.38): C 66.13, H
5.02, N 3.67. Found: C 66.17, H 4.99, N 3.70.
Ethyl 2-benzoyl-4-[(4-methoxybenzyl)amino]-5-oxo-2,5-dihydro-3-furancar- boxylate
(4c)
Yellow oil, yield: 343 mg (87%). IR (KBr): 3300 (NH), 3100, 3000, 1750, 1700, 1670, 1600, 1475, 1465, 1375,
1100 cm−1
;
1 H-NMR δ 6.90-7.81 (m, 9H, arom), 6.35 (s, 1H, CH), 4.83-4.98 (m, 2H, CH2), 4.03 (q, J = 7.25
487

The reaction of dialkyl acetylenedicarboxylates with..., J. SAFAEI-GHOMI, et al.
Hz, 2H, CH2 of Et), 3.67 (s, 3H, MeO), 2.17 (s, 1H, NH), 1.18 (t, J = 7.25 Hz, 3H, CH3). 13 C-NMR δ 192.7,
169.0, 165.4 (3C=O), 159.1, 137.1, 130.4 (3C arom), 135.3, 114.2 (2C alkene), 134.2, 129.1, 129.0, 128.8, 128.7
(9CH arom), 75.8 (CH), 55.3, 60.4 (2CH2), 13.8 (CH3). Ms m/z (%) 395 (M+ , 6), 373 (33), 195 (39), 124
(84), 109 (100). Anal. Calcd. for C22 H21 NO6 (395.41): C 66.83, H 5.35, N 3.54. Found: C 66.80, H 5.39, N
3.49.
Methyl 2-benzoyl-4-[(4-methylbenzyl)amino]-5-oxo-2,5-dihydro-3-furancarboxylate
(4d)
Yellow oil, yield: 299 mg (82%). IR (KBr): 3450 (NH), 3050, 3000, 1735, 1700, 1600, 1475,1465, 1100 cm−1
;
1 H-NMR δ 7.60-8.05 (m, 9H, arom), 6.02 (s, 1H, CH), 4.09-4.16 (m, 2H, CH2), 3.67 (s, 3H, OCH3), 2.20 (s,
3H, CH3), 2.17 (s, 1H, NH). 13 C-NMR δ 192.8, 169.2, 165.6 (3C=O), 136.8, 134.9, 132.2 (3C arom), 135.2,
116.3, (2C alkene), 129.6, 129.1, 128.8, 128.6, 128.3 (9CH arom), 71.4 (CH), 51.2 (MeO), 44.3 (CH2), 21.1
(CH3). Anal. Calcd. for C21 H19 NO5 (365.38): C 69.03, H 5.24, N 3.83. Found: C 69.07, H 5.19, N 3.85.
Ethyl 2-benzoyl-4-[(4-methylbenzyl)amino]-5-oxo-2,5-dihydro-3-furancarboxylate
(4e)
Yellow oil, yield: 288 mg (76%). IR (KBr): 3350 (NH), 3070, 3000, 1750, 1735, 1700, 1600, 1475, 1170 cm−1
;
1 H-NMR δ 6.80-8.21 (m, 9H, arom), 6.02 (s, 1H, CH), 3.42- 3.69 (m, 2H, CH2), 4.10 (q, J=7.25, 2H, CH2 of
Et), 2.30 (s, 3H, CH3), 2.19 (s, 1H, NH), 1.20 (t, J= 7.25, 3H, CH3). 13 C-NMR δ 192.7, 170.1, 166.4 (3C=O),
135.2, 126.0, (C alkene), 135.1, 133.6, 129.5 (3C arom), 129.1, 128.8, 128.6, 128.5, 128.4 (9CH arom), 71.4 (CH),
53.3 (CH2 O), 47.8 (CH2), 14.5, 21.0 (2CH3). Anal. Calcd. for C22 H21 NO5 (379.41): C 69.64, H 5.58, N
3.69. Found: C 69.60, H 5.61, N 3.64.
Methyl 2-benzoyl-4-(benzylamino)- 5-oxo-2,5 dihydro-3-furancarboxylate (4f)
Yellow oil, yield: 288 mg (79%). IR (KBr): 3450 (NH), 3050, 3000, 1750, 1700, 1600, 1475, 1150 cm−1 1 H-
;
NMR δ 7.15-8.30 (m, 10H, arom), 6.09 (s, 1H, CH), 4.14-4.29 (m, 2H, CH2), 3.67 (s, 3H, OCH3), 2.17 (s, 1H,
NH). 13 C-NMR δ 191.9, 169.3, 166.0 (3C=O), 136.5, 132.5 (2C arom), 135.2, 126.0 (2C alkene), 130.3, 129.4,
129.3, 129.3, 126.9, 126.4 (10CH arom), 76.1(CH), 51.2 (MeO), 42.4 (CH2). Anal. Calcd. for C20 H17 NO5
(351.35): C 68.37, H 4.88, N 3.99. Found: C 68.32, H 4.84, N 4.02.
Ethyl 2-benzoyl-4-(benzylamino)-5-oxo-2,5 dihydro-3-furancarboxylate (4g)
Yellow oil, yield: 266 mg (73%). IR (KBr): 3450 (NH), 3050, 3100, 3000, 1750, 1700, 1600, 1475, 1170 cm−1
;
1 H-NMR δ 7.07-8.05 (m, 10H, arom), 6.00 (s, 1H, CH), 4.10 (q, J=7.12, 2H, CH2 of Et), 3.44-3.73 (m, 2H,
CH2), 2.15 (s, 1H, NH), 1.10 (t, J=7.12 Hz, 3H, CH3). 13 C-NMR δ 192.5, 168.5, 164.2 (3C=O), 136.9, 126.4,
(2C alkene), 136.1, 134.3 (2C arom), 134.1, 129.6, 129.3, 129.1, 127.2, 126.1 (10CH arom), 76.1 (CH), 53.9
(CH2 O), 48.1 (CH2), 13.5 (CH3). Anal. Calcd. for C21 H19 NO5 (365.38): C 69.03, H 5.24, N 3.83. Found:
C 69.06, H 5.19, N 3.87.
488

The reaction of dialkyl acetylenedicarboxylates with..., J. SAFAEI-GHOMI, et al.
Methyl-2-benzoyl-4-[(4-fluorobenzyl)amino]-5-oxo-2,5-dihydro-3-furancar- boxylate
(4h)
Yellow oil, yield: 276 mg (75%). IR (KBr): 3400 (NH), 3070, 3000, 1770, 1750, 1700, 1600, 1475, 1150 cm−1
;
1 H-NMR δ 6.91-8.18 (m, 9H, arom), 5.94 (s, 1H, CH), 4.10-4.25 (m, 2H, CH2), 3.41 (s, 3H, OCH3), 2.11 (s, 1H,
1
NH). 13 C-NMR δ 192.1, 170.0, 167.2 (3C=O), 162.8 (d, JCF = 212.2 Hz, C, arom), 143.2, 122.4 (2C alkene),
3
2
135.8, 133.6 (2C arom), 132.4, 130.2, 129.2 (5CH arom), 129.8 (d, JCF = 8.8 Hz, 2CH, arom), 115.3 (d, JCF
= 21.4 Hz, 2CH, arom), 76.1 (CH), 50.4 (MeO), 47.4 (CH2). Anal. Calcd. for C20 H16 FNO5 (369.34): C
65.04, H 4.37, N 3.79. Found: C 65.01, H 4.32, N 3.84.
Ethyl 2-benzoyl-4-[(4-fluorobenzyl)amino]-5-oxo-2,5-dihydro-3-furancarboxylate (4i)
Yellow oil, yield: 268 mg (70%). IR (KBr): 3450 (NH), 3050, 3000, 1750, 1700, 1600, 1475, 1200 cm−1 1 H-
;
NMR δ 6.86-8.20 (m, 9H, arom), 5.97 (s, 1H, CH), 4.20 (q, J=7.0, 2H, CH2 of Et), 3.40- 3.75 (m, 2H, CH2),
1
2.10 (s, 1H, NH), 1.30 (t, J=7.0, 3H, CH3). 13 C-NMR δ 192.8, 168.1, 165.8 (3C=O), 162.0 (d, JCF = 244.7
Hz, C, arom), 142.9, 123.3 (2C alkene), 136.2, 134.5 (2C arom), 132.05, 130.29, 129.1 (5CH arom), 129.9 (d,
2
3JCF = 8.1 Hz, 2CH, arom), 115.3 (d, JCF = 20.8 Hz, 2CH, arom), 76.1 (CH), 54.0 (MeO), 47.3 (CH2), 11.0
(CH3). Anal. Calcd. for C21 H18 FNO5 (383.37): C 65.79, H 4.73, N 3.65. Found: C 65.84, H 4.70, N 3.69.
Methyl 2-benzoyl-5-oxo-4-(propylamino)-2,5 dihydro-3-furancarboxylate (4j)
Yellow oil, yield: 272 mg (90%). IR (KBr): 3350 (NH), 3050, 3000, 2970, 1770, 1700, 1650, 1475, 1120 cm−1
;
1 H-NMR δ 7.50-8.05 (m, 5H, arom), 6.30 (s, 1H, CH), 3.72 (t, J=7.0, 2H, CH2), 3.61 (s, 3H, OCH3), 2.11 (s,
1H, NH), 1.60-1.65 (m, 2H, CH2), 0.90 (t, J=7.0, 3H, CH3). 13 C-NMR δ 165.1, 168.5, 191.1 (3C=O), 134.8,
123.3 (2C alkene), 134.1 (C arom), 132.6, 129.1, 128.8 (5CH arom), 75.4 (CH), 53.4 (MeO), 24.3, 51.2 (2CH2),
11.01(CH3). EI ms: m/z: 303 (M+ , 25), 105 (100), 77 (66), 198 (50), 239 (39). Anal. Calcd. for C16 H17 NO5
(303.31): C 63.36, H 5.65, N 4.62. Found: C 63.32, H 5.69, N 4.58.
Results and discussion
We examined the reaction of the primary amines with dialkyl acetylenedicarboxylate in the presence of 2-
oxo-2-phenylacetaldehyde in dry CH2 Cl2 at room temperature (25 ◦ C) and we obtained the corresponding
alkyl 2-benzoyl-4-alkylamino-5-oxo-2,5-dihydro-3-furan carboxylate derivatives 4 in 70%-95% yields. 1 H and
13 CNMR spectra of the crude products clearly indicated the formation of alkyl 2-benzoyl-4-alkylamino-5-oxo-
2,5-dihydro-3-furan carboxylate 4.
The structures of the products were deduced from their IR, mass, 1 H-NMR, and 13 C-NMR spectra. The
mass spectra of these compounds displayed molecular ion peaks at the appropriate m/z values. The 1 H-NMR
spectrum of 4a consisted of a singlet for NH (δ 2.17), exchangeable by D2 O, 2 singlets for OMe (δ 3.60 and
3.80), a multiplet at δ 4.82-4.98 ppm for CH2 of the benzyl group, a singlet for CH (δ 6.32), and a multiplet at
δ 6.86-8.06 ppm for H-aromatic. The 1 H-decoupled 13 C-NMR spectrum of 4a showed 17 distinct resonances;
489

The reaction of dialkyl acetylenedicarboxylates with..., J. SAFAEI-GHOMI, et al.
partial assignment of these resonances is given in the experimental section. The 1 H- and 13 C-NMR spectra
of compounds 4b-j were similar to those of 4a, except for the aromatic moiety, which exhibited characteristic
signals with appropriate chemical shifts.
A possible mechanism for the present reaction is shown in Scheme 2, which envisages a tandem sequence.
On the basis of the well established chemistry of trivalent nitrogen nucleophiles, the successful nucleophilic
attack by amines on a carbon atom is facilitated when the latter is conjugated with a carbonyl group, or when
it is a part of an unsaturated bond otherwise activated. First, nucleophilic Michael addition of the primary
amine 1 to the β-carbon of the electron-deficient alkyne 2 generates the aminobutendioate 5 as an electron-rich
enaminone.32 The aldehyde carbonyl group, such as 2-oxo-2-phenylacetaldehyde possesses outstanding elec-
trophilic (electron-pair accepting) properties.33 The polar reactions with carbanion-like (electron rich) species,
such as enaminones give rise to nucleophilic addition reactions of carbonyl groups under exclusive C–C bond
formation.34 Subsequent nucleophilic aldol-like attack of aminobutendioate 5 to the aldehyde carbonyl group
of the 2-oxo-2-phenylacetaldehyde 3 would yield iminium–oxoanion intermediate 6, which can be tautomer-
ized to dialkyl 2-(1-hydroxy-2-oxo-2-phenylethyl)-3-(alkylamino)-2-butenedioate 7. γ-Lactonization of 7 would
produce the alkyl 2-benzoyl-4-alkylamino-5-oxo-2,5-dihydro-3-furan carboxylate derivatives 4
O
H
CO2R2
H
H
R2O2C
H
N
R1
O
R1
R2O2C
N
R1NH2
+
O
3
CO2R2
CO2R2
CO2R2
H
1
H
O
5
6
2
iminium-enamine
tautomerization
O
H
R2O2C
N
R1
O
O
H
O
OR2
-R2OH
R2O2C
OH
H
O
R1
N
7
4
Scheme 2. Proposed mechanism for the formation of alkyl 2-benzoyl-4-alkylamino-5-oxo-2,5-dihydro-3- furan carboxy-
late derivatives 4a-j.
490

The reaction of dialkyl acetylenedicarboxylates with..., J. SAFAEI-GHOMI, et al.
Conclusions
The reported method offers a mild, simple, and efficient route for the preparation of alkyl 2-benzoyl-4-
alkylamino-5-oxo-2,5-dihydro-3-furan carboxylate derivatives 4. Its ease of work-up, high yields, and fairly
mild reaction conditions make it a useful addition to modern synthetic methodologies. Other aspects of this
process are under investigation.
Acknowledgements
The authors are grateful to the University of Kashan for supporting this work by Grant No: 65384.
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