Regioselective Ring Opening of Epoxides with Amines Using Silica-bonded S-sulfonic Acid under Solvent-free Conditions

Mahmood Tajbakhsh,* Rahman Hosseinzadeh, Parizad Rezaee, and Heshmatollah Alinezhad

Faculty of Chemistry, Mazandaran University, Babolsar, Iran, Fax: +98 11253 42302.tajbaksh@umz.ac.ir

Received May 2, 2012; ]]> Accepted September 22, 2012

Abstract

Silica-bonded S-sulfonic acid (SBSSA) was used as a recyclable and reusable catalyst for the synthesis of β-amino alcohols. Several amines were reacted with epoxides to afford regioselective β-amino alcohols in high yield under solvent-free conditions at room temperature.

Key words: Silica-bonded S-sulfonic acid, β-amino Alcohols, Epoxides, Amines.

Resumen

Elácido S-sulfónico soportado en sílica gel (ASSSG) se utilizó como un catalizador reciclable y reutilizable para la síntesis de β-aminoalcoholes. Se hicieron reaccionar diversas aminas con epóxidos para dar de manera regioselectiva β-aminoalcoholes en rendimientos altos, a temperatura ambiente y en condiciones libres de disolventes.

Palabra clave: Ácido S-sulfónico soportado en sílica gel, β-aminoalcoholes, epóxidos, aminas.

Epoxides are small molecules with vast synthetic applications. They are able to react with various nucleophiles and their potential to undergo regioselective ring opening reactions adds to their importance as highly useful precursors for the synthesis of organic compounds. Among them, the reaction of epoxides with amines is particularly interesting, because it leads to the formation of β-amino alcohols which are the key intermediates to many organic compounds, including biologically active natural and synthetic products, and chiral auxiliaries for asymmetric synthesis [1-3].

The classical synthetic approach towards β-amino alcohols involves aminolysis of epoxides in protic solvents [4]. There are some limitations to this classical approach such as the requirement of elevated reaction temperatures in the case of less reactive amines, lower reactivity for the sterically crowded amines/epoxides and poor regioselectivity of the epoxide ring opening. To overcome these problems, several activators and promoters have been tried and reported in the literature, including metal salts [5-7], metal amides [8,9], metal alkoxides [10,11], metal triflates [12-14], alumina [15], microwave assisted montmorillonite clay [16], ionicliquids [17], heteropolyacids [18], amberlist-15 [19], thiourea [20], trifluoroethanol [21], silica [22], zeolites [23], organobismuth triflate complex [24], sulphated zirconia and SZ/MCM-41 [25]. However, these methods suffer from one or more disadvantages such as long reaction times [26], elevated temperatures [4, 27], high pressure [22a, 28], moderate yields [18], use of air and moisture sensitive catalysts, requirement of stoichiometric amounts of catalyst, and problems in the recovery of the catalysts [26].

There fore, the development of a highly efficient and a non hazardous catalyst, which is easy to handle, is highly imperative for the synthesis of amino alcohols. Some of these problems can be overcome by employing heterogeneous catalysts, which have several intrinsic advantages like the ease of product separation, recyclability of the catalyst, and the minimization of waste production [22b-c]. In this regard, we focused our attention to solid acids which have emerged as a special class of environmentally friendly catalysts because of their ease of preparation and industrial applications.

SBSSA is a stable solid catalyst which is prepared easily from silica, 3-mercaptopropyltrimethoxysilane and chlorosulfonic acid [29] (Scheme 1). SBSSA has been used as an efficient catalyst in many organic transformations [30]. In this report, we have shown that SBSSA is a highly efficient, mild, reusable and ecofriendly for the ring opening of epoxides under solvent-free conditions at room temperature.

Results and Discussion

To study the effect of catalyst loading on the ring opening of epoxides with amines, the reaction of styrene oxide with aniline was chosen as a model reaction (Table 1). We examined the model reaction in the presence and absence of the catalyst under solvent-free conditions (Table 1). The results in Table 1 showed that a low yield (40%) of the product was formed after 7 h without catalyst (Table 1, entry1), whereas, in the presence of 0.1g SBSSA a high yield of 2-phenylamino-2-phenylethanol was obtained only after 1 h (Table 1, entry 5).

We have also examined the model reaction in various solvents in the presence of 0.1g (0.034 mmol/g) of SBSSA (Table 2). The reaction in solvents gave similar regioselectivity, but required longer reaction time with lower yield of the product than solvent-free conditions (Table 2, entries 1-5).

The generality of this protocol was studied using different amines and epoxides under optimal reaction conditions (Table 3). The results clearly show both steric and electronic effects on the regioselectivity of the reaction. The reaction of styrene epoxide with aromatic amines afforded high ratio of regioisomer A, by nucleophilic attack at the benzylic carbon (Table 3, entries1-9),which could be due to the localized positive charge on the more highly substituted benzylic carbon [31]. Aliphatic amines gave regioisomer B, with the preferential S_N2 attack [32] at the terminal carbon of the epoxides (Table 3, entries 10-12). This reversal regioselectivity was also observed when aliphatic epoxides such as phenyl glycidyl ether and epoxy propyl methacrylate were employed in this reaction (Table 3, entries 13-21). Steric factor seems to be responsible for the observed regioselectivity.

In order to show the advantages and drawbacks of our method, we have compared the model reaction with those reported in the literature in Table 4. As indicated in Table 4, the present method gives higher regioselectivity of 2-phenylamino2-phenylethanol in shorter reaction time.

The reusability and the catalytic activity of SBSSA were investigated in this system. After completion of the reaction, CH₂Cl₂ was added and filtered to remove the catalyst. The recovered catalyst was dried and reused directly for four subsequen truns. Asshownin Table 5, the yield of 2-phenylamino2-phenylethanol decreased slightly after four runs.

In conclusion, a mild, efficient, recyclable and reusable catalyst for the ring opening of epoxides with amines is described. The mild reaction conditions, short reaction times, excellentregio-and chemoselectivity, applicability to both aromatic and aliphatic amines and reusability of the catalyst are main advantages of this method. The solvent-free conditions employed also make it environmentally friendly and potentially useful for industrial applications.

Starting materials used in the reactions were supplied commercially from Aldrich or Merck Chemical Co. ¹H-and ¹³CNMR spectra were recorded on a Bruker DRX-400 AVANCE (400 and 100MHz for ¹H and ¹³C respectively) in CDCl₃ as solvent. SBSSA [29] were prepared according to the reported procedure. Chemical shifts are on the δ scale, relative to internal Me₄Si. Mass spectra were obtained on an Agilent technologies instrument and IR spectra were determined on a Shimadzu instrument.

Catalyst Preparation. Silicagel (Merck,Silica-gel60) was activated by refluxing in concentrated hydrochloric acid (6 M) for 24 h and then washed thoroughly with the deionized water and dried. the activated silica gel (10 g) was refluxed with 3-mercaptopropyltrimethoxysilane (5 mmol) in dry toluene for 18 h, then, the solid was filtered off and washed with hot toluene for 12 h ina continuous extraction apparatus (Soxhlet). The solid was dried in oven at 110 °C overnight to give 3-mercaptopropylsilica 1. To a magnetically stirred mixture of 3-mercaptopropylsilica (1, 5 g) in CHCl₃ (20 mL), was added chlorosulfonic acid (1.00 g, 9 mmol) dropwise at 0 °C during 2 h. After the addition was complete, the mixture was stirred for another 2 h until all HCl was removed from the reaction vessel and then filtered, washed with methanol (30 mL) and dried at room temperature to give the Silica-bonded S-sulfonic acid 2 (SBSSA).

pH analysis of the SBSSA. The SO₃H loading of SBSSA was determined to be 0.34 mmol/g by titration an aqueous suspension of 0.1 g SBSSA with NaOH solution or by pH analysis of an aqueous suspension of 0.1 g SBSSA with NaCl solution (1 M) [29].

General procedure for the ring opening of epoxides. To a magnetically stirred mixture of epoxide (1mmol) and amine (1 mmol), SBSSA catalyst (100mg,3.4mol%) was added and the reaction mixture was stirred at room temperature for appropriate time (Table 3). After completion of the reaction, the mixture was diluted with CH₂Cl₂and filtered off to remove the catalyst. The organic layer was dried (Na₂SO₄) and concentrated under reduced pressure to provide the crude product, which was purified by column chromatography to afford the corresponding β-amino alcohols. All compounds were fully characterized by IR, ¹H NMR and ¹³C NMR data.

Spectral data of all products are as follows:

2-Phenyl-2-(phenylamino) ethanol (Table 3, entry 1). ¹H NMR (400 MHz, CDCl₃): δ 3.04 (broad, exchangeable with D₂O, 2H, NH and OH), 3.74 (dd, J = 7.2 Hz, 11.2 Hz, 1H, CH), 3.93 (dd, J = 4.0 Hz, 11.2 Hz, 1H, CH), 4.52 (dd, J = 4.0 Hz, 7.2 Hz, 1H, CH), 6.63 (d, J = 7.6 Hz, 2H, Ar-CH), 6.75 (t, J = 7.2 Hz, 1H, Ar-CH), 7.17 (t, J = 6.8 Hz, 2H, Ar-CH), 7.30-7.42 (m, 5H, Ar-CH); ¹³C NMR (100 MHz, CDCl₃): δ 59.93, 67.33, 113.95, 117.94, 126.82, 127.64, 128.86, 129.24, 140.24, 147.34.

2-Phenyl-2-(p-tolylamino) ethanol (Table 3, entry 2). ¹H NMR (400 MHz, CDCl₃): δ 2.25 (s, 3H, CH₃), 3.05 (broad, exchangeable with D₂O, 2H, NH and OH), 3.73 (dd, J = 7.2 Hz, 10.8 Hz, 1H, CH₃), 3.94 (dd, J = 4.4 Hz, 11.2 Hz, 1H, CH), 4.50 (dd, J = 4.4 Hz, 7.2 Hz, 1H, CH), 6.55 (d, J = 8.0 Hz, 2H, Ar-CH), 6.97 (d, J = 8.0 Hz, 2H, Ar-CH), 7.29-7.41 (m, 5H, Ar-CH); ¹³C NMR (100 MHz, CDCl₃): δ 20.43, 60.24, 67.35, 114.14, 126.79, 127.19, 127.58,128.82, 129.72, 140.35, 144.96.

2-(4-Methoxyphenylamino)-2-phenylethanol (Table 3, entry 3). ¹H NMR (400 MHz, CDCl₃): δ 3.19 (broad, exchangeable with D₂O, 2H, NH and OH), 3.68-3.74 (m, 4H, CH and OCH₃), 3.91 (dd, J = 4.0 Hz, 11.2 Hz, 1H, CH), 4.43 (dd, J = 4.0 Hz, 7.6 Hz, 1H, CH), 6.56 (d, J = 9.2 Hz, 2H, Ar-CH), 6.73 (d, J = 8.8 Hz, 2H, Ar-CH), 7.29-7.42 (m, 5H, Ar-CH); ¹³C NMR (100 MHz, CDCl₃): δ 55.74, 60.92, 67.31, 114.80, 115.37, 126.81, 127.57, 128.79, 140.45, 141.87, 152.37.

2-(4-Ethoxyphenylamino)-2-phenylethanol (Table 3, entry 4). ¹H NMR (400 MHz, CDCl₃): δ 1.41 (t, J = 7.2 Hz, 3H, CH₃), 3.35 (broad, exchangeable with D₂O, 2H, NH and OH), 3.67 (dd, J = 7.6 Hz, 11.4 Hz, 1H, CH), 3.88 (dd, J = 4.4 Hz, 11.4 Hz, 1H, CH), 3.99 (q, J = 6.8 Hz, 2H, OCH₂), 4.40 (dd, J = 4.4 Hz, 8.0 Hz, 1H, CH), 6.55 (d, J = 10.0 Hz, 2H, Ar-CH), 6.72 (d, J = 8.8 Hz, 2H, Ar-CH), 7.27-7.41 (m, 5H, Ar-CH); ¹³C NMR (100 MHz, CDCl₃): δ 15.02, 60.94, 94.10, 67.28, 115.71, 115.83, 116.70, 126.84,127.50, 128.60, 140.62, 151.94.

2-(4-Bromophenylamino)-2-phenylethanol (Table 3, entry 6). ¹H NMR (400 MHz, CDCl₃): δ 2.07 (broad, exchangeable with D₂O, 2H, NH and OH), 3.76 (dd, J = 6.8 Hz, 12.0 Hz, 1H, CH), 3.95 (dd, J = 4.0 Hz, 11.2 Hz, 1H, CH), 4.26 (dd, J = 4.0 Hz, 6.8 Hz, 1H, CH), 6.484 (d, J = 8.8 Hz, 2H, Ar-CH), 7.19 (d, J = 8.08 Hz, 2H, Ar-CH), 7.28-7.37 (m, 5H, Ar-CH); ¹³C NMR (100 MHz, CDCl₃): δ 59.80, 67.27, 109.49, 115.42, 126.69, 127.80, 128.93, 131.86, 139.56, 146.22.

2-(2-Hydroxy-1-phenylethylamino) benzonitrile (Table 3, entry 7). ¹H NMR (400 MHz, CDCl₃): δ 2.58 (broad, exchangeable with D₂O, 1H, OH), 3.82-3.87 (dd, J = 8.0 Hz, 12.0 Hz, 1H, CH), 3.97-4.01 (dd, J = 8.0 Hz, 12.0 Hz, 1H, CH), 4.58-4.62 (dd, J = 4.0 Hz, 12.0 Hz, 1 H, CH), 5.49 (broad, exchangeable with D₂O, 1H, NH), 6.45 (d, J = 12.0 Hz, 1H, Ar-CH), 6.67 (t, J = 8.0 Hz 1H, Ar-CH), 7.20-7.43 (m, 7H,Ar-CH); ¹³C NMR(100 MHz, CDCl₃): δ 59.53, 66.88, 96.44, 112.37, 117.13, 118.07, 126.62,127.96, 129.00, 132.80, 134.16, 139.01, 149.61; MS (m/z): calc. for C₁₅H₁₄N₂O 238.28 [M]⁺, found 238.20.

2-(4-Nitrophenylamino)-2-phenylethanol (Table 3, entry 8). ¹H NMR (400 MHz, CDCl₃): δ 3.85 (dd, J = 6.4 Hz, 11.2 Hz, ¹H, CH), 4.03 (dd, J =3.6 Hz,11.6 Hz,1H,CH), 4.60 (dd, J = 5.6 Hz, 10.0 Hz, 1H, CH), 5.61 (d, J =5.2, exchangeable with D₂O, 2H, NH and OH), 6.49, (d, J = 9.2 Hz, 2H, Ar-CH), 7.30-7.40 (m, 5H, Ar-CH), 7.99 (d, J = 9.2 Hz, 2H, Ar-CH); ¹³C NMR (100 MHz, CDCl₃): δ 59.29, 66.87, 112.22, 126.24, 126.56, 128.14, 129.11, 138.50, 152.70.

2-(Methyl(phenyl)amino)-2-phenylethanol (Table 3, entry 9). ¹H NMR (400 MHz, CDCl₃): δ 2.62 (broad, exchangeable with D₂O, 1H, OH), 2.79 (s, 3H, CH₃), 4.16 - 4.18 (m 2H, 2CH), 5.15 (t, J = 7.6 Hz, 1H, CH), 6.91 (t, J = 7.2 Hz, 1H, Ar-CH), 7.01 (d, J = 8.0 Hz, 2H, Ar-CH), 7.23 (d, J = 6.8 Hz 2H, Ar-CH), 7.33-7.41 (m, 5H, Ar - CH); ¹³CNMR (100 MHz, CDCl₃): δ 32.15, 61.83, 64.46, 114.64, 118.23, 127.28, 127.64, 128.66, 129.36, 137.79, 151.15.

2-(Cyclohexylamino)-1-phenylethanol (Table 3, entry 10). ¹H NMR (400 MHz, CDCl₃): δ 1.03-1.40 (m, 8H, CH₂), 1.72 1.77 (m, 2H, CH₂), 1.93 (broad, exchangeable with D₂O, 2H, NH and OH), 2.41-2.52 (m,1H,CH), 2.70 (dd, J =9.2Hz,12.0 Hz,1H, CH), 3.00 (dd, J =3.6 Hz,12.2 Hz,1H,CH), 4.70 (dd, J = 3.6 Hz, 9.2 Hz, 1H, CH), 7.28-7.40 (m, 5H, Ar-CH); ¹³C NMR (100 MHz, CDCl₃): δ 25.00, 26.01, 29.71, 33.47, 33.83, 54.15, 56.53, 125.80, 127.44, 128.35, 128.63, 142.70.

1-Phenyl-2-(piperidin-1-yl)ethanol (Table 3, entry 11). ¹H NMR (400 MHz, CDCl₃): δ 1.48-1.52 (m, 2H, CH₂), 1.55-1.69 (m, 5H, CH₂), 2.39-2.44 (m, 3H, CH₂), 2.51 (dd, J = 3.6 Hz, 12.8 Hz, 1H, CH), 2.72 (broad, exchangeable with D₂O, 1H, OH), 4.74 (dd, J = 3.6 Hz, 10.8 Hz, 1H, CH), 7.26-7.41 (m, 5H, Ar-CH); ¹³C NMR (100 MHz, CDCl₃): δ 24.28, 26.14, 26.49, 54.46, 66.94, 68.66, 70.30, 125.86, 127.37, 128.98, 142.47.

2-Morpholino-1-phenylethanol (Table 3, entry 12). ¹H NMR (400 MHz, CDCl₃): δ 2.40-2.59 (m, 6H, CH₂), 2.73 2.76(m, 2H, CH₂),3.59 (dd, J = 5.2 Hz, 8.8 Hz, 1H, CH), 3.97 (dd, J = 8.4 Hz, 10.8 Hz, 1H, CH), 4.77 (dd, J = 3.6 Hz, 10.4 Hz, 1H, CH), 7.26-7.40 (m, 5H, Ar-CH); ¹³C NMR (100 MHz, CDCl₃): δ 53.47, 66.70, 67.02, 67.20, 68.62, 125.85, 127.60, 128.40, 141.90.

1-Phenoxy-3-(phenylamino)propan-2-ol (Table 3, entry 13). ¹H NMR (400 MHz, CDCl₃): δ 3.32 (dd, J = 7.6 Hz, 13.2 Hz, 1H, CH), 3.46 (dd, J = 4.4 Hz, 13.2 Hz, 1H, CH), 3.52 (broad, exchangeable with D₂O, 2H, NH and OH), 4.01-4.10 (m, 2H, CH₂), 4.26-4.30 (m, 1H, CH), 6.74 (d, J = 7.6 Hz, 2H, Ar-CH), 6.84 (t, J = 7.2 Hz, 1H, Ar-CH), 6.99 (d, J = 8.4 Hz, 2H, Ar-CH), 7.07 (t, J =8.0Hz,1H,Ar-CH), 7.28 (t, J =9.2Hz, 2H, Ar-CH), 7.38 (t, J = 9.6 Hz, 2H, Ar-CH); ¹³C NMR (100 MHz, CDCl₃): δ 46.76, 68.82, 70.11, 113.46, 114.66, 118.15, 121.39, 129.45, 129.70, 148.15, 158.51.

1-Phenoxy-3-(p-tolylamino)propan-2-ol (Table 3, entry 14). ¹H NMR (400 MHz, CDCl₃): δ 2.31 (s, 3H, CH₃), 3.29 (dd, J = 8.0 Hz, 12.0 Hz, 1H, CH), 3.38 (broad, exchangeable with D₂O, 2H, NH and OH), 3.44 (dd, J = 4.0 Hz, 16.0 Hz, 1H, CH), 3.90-4.08 (m, 2H, CH₂), 4.25-4.30 (m,1H, CH), 6.66 (d, J = 8.0 Hz, 2H, Ar-CH), 6.98 (d, J = 8.0 Hz, 2H, Ar-CH), 7.03-7.08 (m,3H,Ar-CH), 7.36 (t, J =8.0Hz, 2H, Ar-CH); ¹³C NMR (100MHz, CDCl₃): δ 20.47, 47.17, 68.81, 70.13, 113.65, 114.62, 121.32, 127.41, 129.63, 129.89, 145.81, 158.50.

1-(4-Chlorophenylamino)-3-phenoxypropan-2-ol (Table3, entry 16). ¹H NMR (400 MHz, CDCl₃): δ 3.26 (dd, J = 7.2 Hz, 12.8Hz, 1H, CH), 3.39 (dd, J = 4.0Hz, 13.6Hz, 1H,CH), 3.52 (broad, exchangeable with D₂O, 2H, NH and OH), 3.99-4.08 (m, 2H, CH₂), 4.22-4.28 (m, 1H, CH), 6.60 (d, J = 8.8 Hz, 2H, Ar-CH), 6.95 (d, J = 8.0 Hz, 2H, Ar-CH), 7.04 (t, J = 7.6 Hz, 1H, Ar-CH), 7.16 (d, J = 8.8 Hz, 2H, Ar-CH), 7.34 (t, J = 8.0 Hz, 2H, Ar-CH); ¹³C NMR (100 MHz, CDCl₃): δ 46.73, 68.74, 69.44, 114.58, 114.87, 121.45, 122.56, 129.25, 129.69, 146.69, 158.34.

1-(4-Bromophenylamino)-3-phenoxypropan-2-ol (Table3, entry 17). ¹H NMR (400 MHz, CDCl₃): δ 3.26 (dd, J = 7.6 Hz, 12.8 Hz, 1H, CH), 3.40 (dd, J = 4.4 Hz, 12.8 Hz, 1H, CH), 3.99-4.09 (m, 2H, CH₂), 4.24-4.27 (m, 1H, CH), 6.56 (d, J = 8.4 Hz, 2H, Ar-CH), 6.94 (d, J = 8.0 Hz, 2H, Ar-CH), 7.02 (t, J = 7.6 Hz, 1H, Ar-CH), 7.28 (d, J = 8.8 Hz, 2H, Ar-CH), 7.33 (t, J = 7.6 Hz, 2H, Ar-CH); ¹³C NMR (100 MHz, CDCl₃): δ 46.57, 68.72, 69.94, 109.63, 114.54, 114.87, 121.47, 129.66, 132.03, 147.08, 158.30.

2-Hydroxy-3-(phenylamino)propyl methacrylate (Table 3, entry 18). ¹H NMR (400 MHz, CDCl₃): δ 1.99 (s, 3H, CH₃), 3.19 (dd, J = 7.2Hz, 13.2Hz, 1H, CH), 3.28 (broad, exchangeable with D₂O, 2H, NH and OH), 3.34 (dd, J = 4.4 Hz, 12.8 Hz, 1H, CH), 4.11-4.16 (m, 1H, CH), 4.23-4.31 (m, 2H, CH₂), 5.64 (t, J = 1.6 Hz, 1H, CH), 6.18 (t, J = 1.2 Hz, 1H, CH), 6.67 (d, J = 7.6 Hz, 2H, Ar-CH), 6.77 (t, J = 7.2 Hz, 1H, Ar-CH), 7.21 (t, J = 7.2 Hz, 2H, Ar-CH); ¹³C NMR (100 MHz, CDCl₃): δ 18.35, 46.69, 66.81, 68.44, 113.33, 118.11, 126.44, 129.37, 135.87, 147.94, 167.64.

2-Hydroxy-3-(p-tolylamino)propyl methacrylate (Table 3, entry 19). ¹H NMR (400 MHz, CDCl₃): δ 1.99 (s, 3H, CH), 2.27 (s, 3H, CH₃), 3.16 (dd, J = 7.6Hz, 16.0Hz, 1H, CH), 3.32 (dd, J = 4.0 Hz, 13.2 Hz, 1H, CH), 3.43 (broad, exchangeable with D₂O, 2H, NH and OH), 4.10-4.15 (m, 1H, CH), 4.22-4.30 (m, 2H, CH₂), 5.64 (t, J = 1.6, 1H, CH), 6.18 (s, 1H, CH), 6.60 (d, J = 8.4 Hz, 2H, Ar-CH), 7.02 (d, J = 8.0 Hz, 2H, Ar-CH); ¹³C NMR (100 MHz, CDCl₃): δ 18.35, 20.40, 47.16, 66.84, 68.42, 113.61, 126.37, 127.43, 129.84, 135.90, 145.63, 167.61.

3-(4-Chlorophenylamino)-2-hydroxypropyl methacrylate (Table 3, entry 20). ¹H NMR (400 MHz, CDCl₃): δ 1.99 (s, 3H, CH), 3.16 (dd, J = 7.6 Hz, 13.0 Hz, 1H, CH), 3.30 (dd, J = 4.4 Hz, 12.8 Hz, 1H, CH), 4.10-4.15 (m, 1H, CH), 4.23-4.31 (m, 2H, CH₂), 5.64 (t, J = 1.2, 1H, CH), 6.17 (s, 1H, CH), 6.58 (d, J = 8.8 Hz, 2H, Ar-CH), 7.13 (d, J = 8.8 Hz, 2H, Ar-CH); ¹³C NMR (100 MHz, CDCl₃): δ 18.33, 46.71, 66.80, 68.50, 114.36, 122.64, 126.53, 129.15, 135.78, 146.51, 167.62.

3-(4-Bromophenylamino)-2-hydroxypropyl methacrylate (Table 3, entry 21). ¹H NMR (400 MHz, CDCl₃): δ 1.95 (s, 3H, CH), 3.11 (dd, J = 7.6 Hz, 13.2 Hz, 1H, CH), 3.25 (dd, J = 7.6 Hz, 14.0 Hz, 1H, CH), 4.05-4.11 (m, 1H, CH), 4.22 (d, J = 5.2 Hz, 2H, CH₂), 5.62 (t, J = 1.2, 1H, CH), 6.15 (s, 1H, CH), 6.50 (d, J = 8.8 Hz, 2H, Ar-CH), 7.23 (d, J = 8.8 Hz, 2H, Ar-CH); ¹³C NMR (100 MHz, CDCl₃): δ 18.33, 46.58, 66.69, 68.29, 109.46, 114.80, 126.63, 131.98, 135.77, 147.02, 167.69.

Acknowledgement

Financial support of this work from the Research Council of University of Mazandran gratefully acknowledged, Iran.

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