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Communication

Efficient Synthesis of β-Enaminones and β-Enaminoesters Catalyzed by Gold (I)/Silver (I) under Solvent-Free Conditions

by
Ming Zhang
1,
Ablimit Abdukader
1,2,
Yong Fu
1 and
Chengjian Zhu
1,3,*
1
State Key Laboratory of Coordination Chemistry, School of Chemistry and Chemical Engineering, Nanjing University, Nanjing 210093, China
2
School of Chemistry and Chemical Engineering, Xinjiang University, Urumqi 830046, China
3
State Key Laboratory of Organometallic Chemistry, Shanghai Institute of Organic Chemistry, Chinese Academy of Sciences, Shanghai 200032, China
*
Author to whom correspondence should be addressed.
Molecules 2012, 17(3), 2812-2822; https://doi.org/10.3390/molecules17032812
Submission received: 15 January 2012 / Revised: 16 February 2012 / Accepted: 17 February 2012 / Published: 6 March 2012
(This article belongs to the Section Organic Chemistry)
Browse Figure
Versions Notes

Abstract

:
An efficient method for the synthesis of β-enaminones and β-enaminoesters using a combination of [(PPh3)AuCl]/AgOTf as catalyst has been developed. The reaction between 1,3-dicarbonyl compounds and primary amines was carried out under solvent-free conditions with low catalyst loading in good to excellent yields at room temperature.

1. Introduction

β-Enaminones and β-enaminoesters are highly useful building blocks [1,2,3], which can be further transformed into valuable natural therapeutic and biologically active compounds such as anticonvulsivant [4,5], anti-inflammatory [6], and antitumor agents [7,8]. Moreover, they are useful intermediates for the preparation of aminoesters [9], α,β-aminoacids [10,11], peptides [12], quinolines [13,14], azocompounds [15,16] and alkaloids [17,18,19]. Owning to their significances in organic synthesis, considerable efforts have been dedicated to prepare β-enaminones and β-enamino-esters. One of the most straightforward methods is condensation between 1,3-dicarbonyls and amines under reflux conditions [20]. Other improved methods for this amination reaction were successively developed [21,22,23,24,25,26,27,28,29,30,31,32,33,34]. However, in these procedures, the long reaction time, high reaction temperatures, and high catalyst loadings required could limit their further applications in organic synthesis.
Gold (I) and gold (III) salts have emerged as versatile catalysts to facilitate new carbon-carbon or carbon-heteroatom bond formation in a variety of reactions [35,36,37,38]. In 2003, Arcadi reported that gold (III) derivatives could catalyze the condensation reaction of 1,3-dicarbonyls and ammonia/amines [27], however, when the aromatic amine had been involved in the reaction only 60% yield was obtained. With increasing attention being paid to economically simple and environmentally safe methods, the recent trends in organic reaction are oriented to solvent-free conditions [39,40,41]. Herein, we report a practical method for the synthesis of β-enaminones and β-enaminoesters under solvent-free conditions by using [(PPh3)AuCl]/AgOTf as catalyst with lower catalyst loading at room temperature (Scheme 1).
Molecules 17 02812 g001 550
Scheme 1. Gold (I)/silver (I) catalyzed enamination of β-dicarbonyl compounds.
Scheme 1. Gold (I)/silver (I) catalyzed enamination of β-dicarbonyl compounds.
Molecules 17 02812 g001

2. Results and Discussion

Initially, the reaction between acetylacetone and 4-methoxyaniline was carried out without catalyst under solvent-free conditions at room temperature for 2 h; only 25% yield of the desired product could be obtained (Table 1, entry 1). The salt (PPh3)AuCl (1 mol%) indicated moderate catalytic activity (33% yield) (Table 1, entry 2), while the silver salt AgOTf (1 mol%) afforded a lower yield (28% yield) (Table 1, entry 3). Surprisingly, by combining (PPh3)AuCl (1 mol%) with AgOTf (1 mol%) as cocatalyst, the product could be obtained in higher yield (98%) than when a single salt was used (Table 1, entry 4), so (PPh3)AuCl/AgOTf was chosen as a promising catalyst for the reaction. The reaction was found to be sluggish when dichloromethane (DCM, 1 mL) was chosen as solvent (Table 1, entry 5). Various amines were examined in this enamination reaction with acetylacetone, and the corresponding β-enaminones were obtained in excellent yields (85%–98%). The results are listed in Table 2.
Table
Table 1. Screening of the reaction conditions for the enamination a. Molecules 17 02812 i001
Table 1. Screening of the reaction conditions for the enamination a. Molecules 17 02812 i001
EntryCatalystTime (h)Yield (%) b
1-225
2(PPh3)AuCl233
3AgOTf228
4(PPh3)AuCl + AgOTf298
5c(PPh3)AuCl + AgOTf685
a Reaction conditions: See typical procedure; b Isolated yield; c The reaction was carried out in DCM.
Table
Table 2. Synthesis of β-enaminones with [(PPh3)AuCl]/AgOTf under solvent-free conditions a. Molecules 17 02812 i002
Table 2. Synthesis of β-enaminones with [(PPh3)AuCl]/AgOTf under solvent-free conditions a. Molecules 17 02812 i002
Entry2 (R1)Time3Yield (%) b
14-CH3OC6H42 h Molecules 17 02812 i00398
2C6H5 4 h Molecules 17 02812 i00485
34-CH3C6H43 h Molecules 17 02812 i00587
44-BrC6H44 h Molecules 17 02812 i00690
54-ClC6H4 5 h Molecules 17 02812 i00788
6C10H75 h Molecules 17 02812 i008 96
7Bn5 min Molecules 17 02812 i009 3g95
8n-C4H95 min Molecules 17 02812 i010 3h96
9Allyl1.5 h Molecules 17 02812 i011 3i98
102-Hydroxyethyl5 min Molecules 17 02812 i012 3j96
a Reaction conditions: See typical procedure; b Isolated yield.
We then extended the scope of various amines with β-ketoesters using 1 mol% loading of [(PPh3)AuCl]/AgOTf catalyst, and the results are summarized in Table 3. All the desired products could be obtained in high yields (76–98%). In addition, high chemoselectivity and regioselectivity can be obtained in this reaction since the ester group is less electrophilic than the keto carbonyl group; and only a single product was observed when the reaction was carried out between amine and β-ketoesters. Generally, the electronic properties of the aryl group appeared to slightly influence the reactivity. It is clear from our results that aromatic amines containing electron-donating groups like methoxyl and methyl (Table 3, entries 2 and 3) give the corresponding products in higher yields compared to the electron-withdrawing ones (Table 3, entries 4 and 5). Aliphatic amines (Table 3, entries 7–10) were more reactive than aromatic amines (Table 3, entries 1–6), and the reactions were completed within a shorter time. Furthermore, cyclic β-ketoesters could also afford the desired product in high yields (Table 3, entries 11–16).
Table
Table 3. Synthesis of β-enaminoesters with [(PPh3)AuCl]/AgOTf under solvent-free conditions a. Molecules 17 02812 i013
Table 3. Synthesis of β-enaminoesters with [(PPh3)AuCl]/AgOTf under solvent-free conditions a. Molecules 17 02812 i013
Entry2 (R1)4Time5Yield (%) b
14-CH3OC6H44a3 h Molecules 17 02812 i014 5a98
2C6H5 4a5 h Molecules 17 02812 i015 5b82
34-CH3C6H44a4 h Molecules 17 02812 i016 5c92
44-BrC6H44a5 h Molecules 17 02812 i017 5d86
54-ClC6H4 4a5 h Molecules 17 02812 i018 5e76
6C10H74a8 h Molecules 17 02812 i019 5f85
7Bn4a5 min Molecules 17 02812 i020 5g97
8n-C4H94a5 min Molecules 17 02812 i021 5h95
9Allyl4a1 h Molecules 17 02812 i022 5i97
102-Hydroxyethyl4a5 min Molecules 17 02812 i023 5j96
114-CH3OC6H44b2 h Molecules 17 02812 i024 5k93
12C6H5 4b2 h Molecules 17 02812 i025 5l87
134-CH3C6H44b1.5 h Molecules 17 02812 i026 5m94
144-BrC6H44b2 h Molecules 17 02812 i027 5n92
154-ClC6H4 4b2 h Molecules 17 02812 i028 5o90
16C10H74b2 h Molecules 17 02812 i029 5p90
17Bn4b5 min Molecules 17 02812 i030 5q85
a Reaction conditions: See typical procedure; b Isolated yield.

3. Experimental

3.1. General

All reagents were obtained from commercial suppliers and used without further purification. Solvents were dried and distilled prior to use according to standard methods. The reaction was monitored by TLC on silica-gel plates (GF 254). 1H- (300 MHz) and 13C-NMR (75 MHz) spectra were recorded on a Bruker APX-300 spectrometer at room temperature in CDCl3 using tetramethylsilane (TMS) as the internal standard. The coupling constants J are given in Hz. All yields mentioned referred to isolated yields.

3.2. Preparation of (PPh3)AuCl

The reaction was carried out in the absence of light. SMe2 (10 mmol) was added to a solution of HAuCl4·2H2O (5 mmol) in MeOH (5 mL), and the mixture was stirred for 10 minutes. The white precipitate [AuCl(SMe2)] from solution was then filtered, subsequently washed with MeOH, Et2O and hexane, then dried under vacuum and used in the next step without further purification. Triphenylphosphine (2 mmol) was added to a stirred solution of [AuCl(SMe2)] (2 mmol) in CH2Cl2 (15 mL) under a nitrogen atmosphere. After stirring at room temperature for 30 minutes, the volume of the solution was reduced to 5 mL under reduced pressure, and then hexane (20 mL) was added, resulting in the precipitation of the complex. The solid was then filtered, washed with hexane and dried, resulting in the quantitative isolation of complex [(PPh3)AuCl] as a pale yellow solid (97%). The complex was characterized only by 31P-NMR spectroscopy [42,43].

3.3. Typical Procedure for the Synthesis of β-Enaminones and β-Enaminoesters

The reaction was carried out without inert atmosphere and light protection. A mixture of (PPh3)AuCl (0.03 mmol), AgOTf (0.03 mmol) and 1,3-dicarbonyl compound (3 mmol) was stirred at room temperature for 5 minutes, then amine (3 mmol) was added into the stirring solution. The reaction was monitored by TLC on silica-gel plates (GF 254). After the reaction was complete, the residue was diluted with water (10 mL) and extracted with ethyl acetate (3 × 10 mL). The combined organic extracts were dried over anhydrous Na2SO4 and concentrated under reduced pressure after filtration. Further purification by flash chromatography gave the corresponding product.
(Z)-4-(4-Methoxyphenylamino)pent-3-en-2-one (3a). 1H-NMR δ = 12.31 (s, 1H), 7.03–7.05 (m, 2H), 6.86–6.88 (m, 2H), 5.16 (s, 1H), 3.79 (s, 3H), 2.08 (s, 3H), 1.90 (s, 3H); 13C-NMR δ = 195.78, 161.15, 157.60, 131.35, 126.54, 114.13, 96.79, 55.33, 28.99, 19.54.
(Z)-4-(Phenylamino)pent-3-en-2-one (3b). 1H-NMR δ = 12.44 (s, 1H), 6.96–7.23 (m, 5H), 5.09 (s, 1H), 1.99 (s, 3H), 1.87 (2, 3H); 13C-NMR δ = 195.45, 159.62, 138.18, 128.59, 124.98, 124.05, 97.18, 28.66, 19.30
(Z)-4-(p-Tolylamino)pent-3-en-2-one (3c). 1H-NMR δ = 12.39 (s, 1H), 7.07 (d, 2H, J = 8.4 Hz), 6.92 (d, 2H, J = 8.4 Hz), 5.12 (s, 1H), 2.27 (s, 3H), 2.04 (s, 3H), 1.89 (s, 3H); 13C-NMR δ = 195.67, 160.51, 135.91, 135.27, 129.54, 124.62, 97.13, 28.98, 20.77, 19.61
(Z)-4-(4-Bromophenylamino)pent-3-en-2-one (3d). 1H-NMR δ = 12.38 (s, 1H), 7.34 (d, 2H, J = 12 Hz), 6.88 (d, 2H, J = 12 Hz), 5.13 (s, 1H), 2.01 (s, 3H), 1.90 (s, 3H); 13C-NMR δ = 196.31, 159.32, 137.74, 132.02, 125.83, 118.43, 98.16, 29.13, 19.70.
(Z)-4-(4-Chlorophenylamino)pent-3-en-2-one (3e). 1H-NMR δ = 12.38 (s, 1H), 7.18–7.22 (m, 2H), 6.92–6.96 (m, 2H), 5.12 (s, 1H), 2.01 (s, 3H), 1.89 (s, 3H); 13C-NMR δ = 196.3, 159.5, 137.2, 129.1, 125.6, 98.0, 29.1, 19.7.
(Z)-4-(Naphthalen-1-ylamino)pent-3-en-2-one (3f). 1H-NMR δ = 12.80 (s, 1H), 8.02–8.05 (m, 1H), 7.83–7.86 (m, 1H), 7.72–7.75 (m, 1H), 7.49–7.55 (m, 2H), 7.39–7.44 (m, 1H), 7.23–7.26 (m, 1H), 5.31 (s, 1H), 2.12 (s, 3H), 1.85 (s, 3H); 13C-NMR δ = 196.4, 161.8, 134.7, 134.1, 129.8, 128.2, 126.8, 126.7, 126.5, 125.2, 123.3, 122.6, 97.5, 29.2, 19.6.
(Z)-4-Benzylamino)pent-3-en-2-one (3g). 1H-NMR δ = 11.17 (s, 1H), 7.22–7.34 (m, 5H), 5.03 (s, 1H), 4.44 (d, 2H, J = 6.3 Hz), 2.02 (s, 3H), 1.88 (2, 3H); 13C-NMR δ = 195.1, 162.9, 137.8, 128.6, 127.2, 126.5, 95.7, 77.4, 77.0, 76.6, 46.4, 28.7, 18.7.
(Z)-4-(Butylamino)pent-3-en-2-one (3h). 1H-NMR δ = 10.80 (s, 1H), 4.87 (s, 1H), 3.15 (q, 2H, J = 6.6 Hz), 1.91 (s, 3H), 1.84 (s, 3H), 1.44–1.54 (m, 2H), 1.27–1.39 (m, 2H), 0.85 (q, 3H, J = 7.2 Hz); 13C- NMR δ = 194.3, 162.9, 94.7, 42.4, 31.9, 28.5, 19.8, 19.7, 18.6, 13.5, 13.5.
(Z)-4-(Allylamino)pent-3-en-2-one (3i). 1H-NMR δ = 10.70 (s, 1H), 5.64–5.73 (m, 2H), 4.97–5.07 (m, 2H), 4.83 (s, 3H), 3.67–3.71(m, 2H), 1.82 (s, 1H), 1.74(s, 1H); 13C-NMR δ = 194.7, 162.9, 133.9, 115.7, 95.4, 44.8, 28.6, 18.3.
(Z)-4-(2-Hydroxyethylamino)pent-3-en-2-one (3j). 1H-NMR δ = 10. 71 (s, 1H), 5.02 (s, 1H), 4.83 (s, 1H), 3.60 (t, 2H, J = 5.4 Hz), 3.27 (t, 2H, J = 5.4 Hz), 1.83 (s, 6H); 13C-NMR δ = 194.3, 164.1, 95.3, 61.0, 45.3, 28.3, 18.9.
(Z)-Ethyl 3-(4-Methoxyphenylamino)but-2-enoate (5a). 1H-NMR δ = 10.15 (s, 1H), 6.97–7.00 (m, 2H), 6.80–6.83 (m, 2H), 4.62 (s, 1H), 4.07–4.14 (q, 2H, J = 7.0 Hz), 3.75 (s, 3H), 1.85 (s, 3H), 1.24 (t, 3H, J = 7.0 Hz); 13C-NMR δ = 170.3, 159.7, 157.2, 131.9, 126.5, 113.9, 84.5, 58.4, 55.1, 19.9, 14.4.
(Z)-Ethyl 3-(Phenylamino)but-2-enoate (5b). 1H-NMR δ = 10.43 (s, 1H), 7.27–7.32 (m, 2H), 7.05–7.15 (m, 3H), 4.70 (s, 1H), 4.11–4.18 (q, 2H, J = 7.2 Hz), 1.97 (s, 3H), 1.27 (t, 3H, J = 7.2 Hz); 13C-NMR δ = 170.3, 158.8, 139.2, 120.0, 124.8, 124.2, 86.0, 58.6, 20.2, 14.5.
(Z)-Ethyl 3-(p-Tolylamino)but-2-enoate (5c). 1H-NMR δ = 10.32 (s, 1H), 7.10–7.13 (m, 2H), 6.95–6.98 (m, 2H), 4.67 (s, 1H), 4.14 (q, 2H, J = 7.2 Hz), 2.32 (s, 3H), 1.94 (s, 3H), 1.28 (t, 3H, J = 7.2 Hz). 13C-NMR δ = 170.3, 159.3, 136.6, 134.7, 129.5, 124.6, 85.3, 58.6, 20.8, 20.1, 14.5.
(Z)-Ethyl 3-(4-Bromophenylamino)but-2-enoate (5d). 1H-NMR δ = 10.34 (s, 1H), 7.34–7.37 (m, 2H), 6.88–6.89 (m, 2H), 4.67 (s, 1H), 4.06–4.13 (q, 2H, J = 7.2 Hz), 1.93 (s, 3H), 1.23 (t, 3H, J = 7.2 Hz); 13C-NMR δ = 170.2, 158.0, 138.4, 132.0, 125.5, 117.7, 87.0, 58.8, 20.1, 14.5.
(Z)-Ethyl 3-(4-Chlorophenylamino)but-2-enoate (5e). 1H-NMR δ = 10.36 (s, 1H), 7.24–7.27 (m, 2H), 6.97–7.00 (m, 2H), 4.70 (s, 1H), 4.12 (q, 2H, J = 7.2 Hz), 1. 95 (s, 3H), 1.26 (t, 3H, J = 7.2 Hz). 13C-NMR δ = 170.3, 158.2, 137.9, 130.1, 129.1, 125.3, 116.1, 86.8, 58.8, 20.1, 14.5.
(Z)-Ethyl 3-(Naphthalen-1-ylamino)but-2-enoate (5f). 1H-NMR δ = 10.68 (s, 1H), 8.10–8.13 (m, 1H), 7.87–7.90 (m, 1H), 7.74–7.77 (m, 1H), 7.52–7.57 (m, 2H), 7.42–7.47 (m, 1H), 7.27–7.29 (m, 1H), 4.88 (s, 1H), 4.27 (q, 2H, J = 7.2 Hz), 1. 89 (s, 3H), 1.37 (t, 3H, J = 7.2 Hz). 13C-NMR δ = 170.7, 160.4, 135.3, 134.2, 130.4, 128.2, 126.7, 126.5, 126.4, 125.3, 123.5, 122.7, 85.8, 58.8, 20.0, 14.7.
(Z)Ethyl 3-(Benzylamino)but-2-enoate (5g). 1H-NMR δ = 8.96 (s, 1H), 7.21–7.29 (m, 5H), 4.53 (s, 1H), 4.34 (s, 2H), 4.04–4.11 (m, 3H), 1.84 (t, 3H, J = 3.6 Hz), 1.18–1.24 (m, 3H); 13C-NMR δ = 170.4, 161.7, 138.7, 128.7, 127.2, 126.6, 83.1, 58.2, 46.6, 19.2, 14.5.
(Z)-Ethyl 3-(Butylamino)but-2-enoate (5h). 1H-NMR δ = 8.46 (s, 1H), 4.31 (s, 1H), 3.96 (q, 2H, J = 7.2 Hz), 3.06–3.13 (m, 2H), 1.81 (s, 3H), 1.40–1.49 (m, 2H), 1.24–1.36 (m, 2H), 1.13 (t, 3H, J = 7.2 Hz), 0.83 (t, 3H, J = 7.2 Hz); 13C-NMR δ = 170.4, 161.7, 81.5, 57.9, 42.5, 32.3, 19.8, 19.1, 14.4, 13.6.
(Z)-Ethyl 3-(Allylamino)but-2-enoate (5i). 1H NMR (CDCl3, 300 MHz) δ = 8.61 (s, 1H), 5.74–5.85 (m, 1H), 5.06–5.19 (m, 2H), 4.42 (s, 1H), 4.02 (q, 2H, J = 7.2 Hz), 3.75–3.80 (m, 2H), 1.85 (s, 3H), 1.18 (t, 3H, J = 7.2 Hz); 13C NMR (CDCl3, 75 MHz) δ = 170.4, 161.7, 134.7, 115.6, 82.6, 58.1, 45.0, 18.9, 14.5.
(Z)-Ethyl 3-(2-Hydroxyethylamino)but-2-enoate (5j). 1H NMR (CDCl3, 300 MHz) δ = 8.61 (s, 1H), 4.44 (s, 1H), 4.04 (q, 2H, J = 7.2 Hz), 3.70 (t, 2H, J = 5.4 Hz), 3.13 (br, 1H), 3.33 (q, 2H, J = 5.4 Hz), 1.91 (s, 1H), 1.21 (t, 3H, J = 7.2 Hz); 13C NMR (CDCl3, 75 MHz) δ = 170.7, 162.1, 82.6, 61.8, 58.4, 45.0, 19.5, 14.5.
Ethyl 2-(4-Methoxyphenylamino)cyclopent-1-enecarboxylate (5k). 1H-NMR δ = 9.32 (s, 1H), 6.90–6.93 (m, 2H), 6.74–6.77 (m, 2H) , 4.14 (q, 2H, J = 7.2 Hz), 3.69 (s, 1H), 2.49–2.60 (m, 4H), 1.71–1.80 (m, 2H), 1.25 (t, 3H, J = 7.2 Hz); 13C-NMR δ = 168.3, 161.4, 156.1, 133.6, 123.3, 114.1, 95.9, 58.6, 55.2, 33.1, 28.8, 21.5, 14.6.
Ethyl 2-(Phenylamino)cyclopent-1-enecarboxylate (5l). 1H-NMR δ = 9.65 (s, 1H), 7.24–7.30 (m, 2H), 6.99–7.05 (m, 3H) , 4.21 (q, 2H, J = 7.2 Hz), 2.79 (t, 2H, J = 7.2 Hz), 2.58 (t, 2H, J = 7.2 Hz), 1.86 (m, 2H), 1.32 (t, 3H, J = 7.2 Hz); 13C-NMR δ = 168.4, 160.3, 140.6, 129.1, 123.0, 120.6, 97.6, 58.9, 33.6, 28.7, 21.7, 14.6.
Ethyl 2-(p-Tolylamino)cyclopent-1-enecarboxylate (5m). 1H-NMR δ = 9.55 (s, 1H), 7.05–7.08 (m, 2H), 6.92–6.94 (m, 2H), 4.21 (q, 2H, J = 7.2 Hz), 2.73 (t, 2H, J = 7.2 Hz), 2.57(t, 2H, J = 7.2 Hz), 2.29 (s, 3H), 1.84 (m, 2H), 1.31(t, 3H, J = 7.2 Hz); 13C-NMR δ = 168.4, 160.8, 138.1, 132.7, 129.6, 121.0, 96.8, 58.8, 33.4, 28.7, 21.7, 20.6, 14.6.
Ethyl 2-(4-Bromophenylamino)cyclopent-1-enecarboxylate (5n). 1H-NMR δ = 9.61 (s, 1H), 7.30–7.35 (m, 2H), 6.83–6.88 (m, 2H) , 4.11 (q, 2H, J = 7.2 Hz), 2.72 (t, 2H, J = 7.2 Hz), 2.53 (t, 2H, J = 7.2 Hz), 1.83 (m, 2H), 1.28 (t, 3H, J = 7.2 Hz); 13C-NMR δ = 168.3, 159.4, 139.7, 132.0, 121.7, 115.4, 98.6, 59.0, 33.5, 28.6, 21.7, 14.6.
Ethyl 2-(4-Chlorophenylamino)cyclopent-1-enecarboxylate (5o). 1H-NMR δ = 9.60 (s, 1H), 7.16–7.19 (m, 2H), 6.89–6.92 (m, 2H) , 4.16 (q, 2H, J = 7.2 Hz), 2.72 (t, 2H, J = 7.2 Hz), 2.53 (t, 2H, J = 7.2 Hz), 1.83 (m, 2H), 1.27 (t, 3H, J = 7.2 Hz); 13C-NMR δ = 168.3, 159.5, 139.2, 129.0, 127.9, 121.4, 98.4, 59.0, 33.5, 28.6, 21.6, 14.5.
Ethyl 2-(Naphthalen-1-ylamino)cyclopent-1-enecarboxylate (5p). 1H-NMR δ = 10.02 (s, 1H), 8.18–8.21 (m, 1H), 7.85–7.88 (m, 1H), 7.52–7.66 (m, 3H), 7.38–7.44 (m, 1H), 7.22–7.25 (m, 1H), 7.27–7.29 (m, 1H), 4.33 (q, 2H, J = 7.2 Hz), 2.69 (m, 4H), 1. 86 (m, 2H), 1.40 (t, 3H, J = 7.2 Hz); 13C-NMR δ = 168.8, 161.6, 136.3, 134.3, 128.3, 126.4, 126.3, 125.4, 124.6, 122.0, 119.0, 97.7, 59.0, 33.4, 29.0, 21.6, 14.8.
Ethyl 2-(Benzylamino)cyclopent-1-enecarboxylate (5q). 1H-NMR δ = 7.80 (s, 1H), 7.25–7.35 (m, 5H), 4.38 (d, 2H, J = 6.6 Hz) , 4.16 (q, 2H, J = 7.2 Hz), 2.54 (q, 4H, J = 7.2 Hz), 1.81 (m, 2H), 1.28 (t, 3H, J = 7.2 Hz); 13C-NMR δ = 168.4, 164.5, 139.2, 128.6, 127.2, 126.7, 93.4, 58.4, 48.3, 32.0, 29.1, 20.8, 14.7.

4. Conclusions

In summary, we have developed an efficient method for the synthesis of β-enaminones and β-enaminoesters via reaction of 1,3-dicarbonyl compounds with various primary amines under solvent-free conditions catalyzed by [(PPh3)AuCl]/AgOTf. This methodology affords various β-enaminones and β-enaminoesters derivatives in good to excellent yields. Moreover, the method has the advantage of easy manipulation and mild reaction conditions.

Acknowledgements

We gratefully acknowledge the National Natural Science Foundation of China (20832001, 20972065, 21074054, 21172106) and the National Basic Research Program of China (2010CB923303) for their financial support.
  • Sample Availability: Samples of the compounds are available from the authors.

References and Notes

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MDPI and ACS Style

Zhang, M.; Abdukader, A.; Fu, Y.; Zhu, C. Efficient Synthesis of β-Enaminones and β-Enaminoesters Catalyzed by Gold (I)/Silver (I) under Solvent-Free Conditions. Molecules 2012, 17, 2812-2822. https://doi.org/10.3390/molecules17032812

AMA Style

Zhang M, Abdukader A, Fu Y, Zhu C. Efficient Synthesis of β-Enaminones and β-Enaminoesters Catalyzed by Gold (I)/Silver (I) under Solvent-Free Conditions. Molecules. 2012; 17(3):2812-2822. https://doi.org/10.3390/molecules17032812

Chicago/Turabian Style

Zhang, Ming, Ablimit Abdukader, Yong Fu, and Chengjian Zhu. 2012. "Efficient Synthesis of β-Enaminones and β-Enaminoesters Catalyzed by Gold (I)/Silver (I) under Solvent-Free Conditions" Molecules 17, no. 3: 2812-2822. https://doi.org/10.3390/molecules17032812

APA Style

Zhang, M., Abdukader, A., Fu, Y., & Zhu, C. (2012). Efficient Synthesis of β-Enaminones and β-Enaminoesters Catalyzed by Gold (I)/Silver (I) under Solvent-Free Conditions. Molecules, 17(3), 2812-2822. https://doi.org/10.3390/molecules17032812

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