HETEROCYCLES

Paper | Regular issue | Vol. 81, No. 9, 2010, pp. 2087-2096
Received, 7th June, 2010, Accepted, 30th July, 2010, Published online, 3rd August, 2010.
DOI: 10.3987/COM-10-11987

■ An Efficient Synthesis of 2-Aminobenzoxazoles and 2-Aminobenzothiazoles from 2-Aminophenols or 2-Aminothiophenols and Isoselenocyanates

Yuanyuan Xie,* Fan Zhang, Xiaodong Chen, and Jianjun Li

Key Laboratory of Pharmaceutical Engineering of Ministry of Educations, College of Pharmaceutical Sciences, Zhejiang University , Hangzhou 310014, China

Abstract

An expeditious method to access 2-aminobenzoxazoles and 2-aminobenzothiazoles from various substituted 2-aminophenols and 2-aminothiophenols, respectively, with isoselenocyanates in a one pot procedure is reported. Elemental Se precipitates nearly quantitatively in the reaction without any deselenizing agent and it can be reused. A possible mechanism for the formation of the target products is proposed.

INTRODUCTION
In the past two decades, the chemistry of organoselenium compounds has attracted much attention because of their importance as synthetic tools.1 Remarkable jobs have been done by Heimgartner’s group and other research groups for the utility of isoselenocyanates as building blocks in the synthesis of Se-containing heterocycles.2
However, reactions with isoselenocyanates to give corresponding non-Se-containing heterocycles have not been studied profoundly. So far as we know, Fernández-Bolaños and his co-workers discovered the phenomenon that elemental Se precipitated from unprotected glycopyranosyl selenoureas which were synthesized from isoselenocyanates and glycopyranosylamines to give bicyclic isoureas.3 Very recently, we have reported the preparation of 2-aminobenzimidazoles by the reaction of isoselenocyanates and o-phenylenediamines.4
2-Aminobenzoxazole and 2-aminobenzothiazole are known as biologically active compounds in many pharmaceuticals and agrochemicals.5 For example, 2-aminobenzoxazole shows activity against inhibitors or modulators of histamine receptors and is regarded as a drug candidate for the treatment of HIV, neurodegeneration, and inflammatory diseases.6
Therefore, there has been an enhanced interest in the synthesis of 2-aminobenzoxazoles and 2-aminobenzothiazoles. The traditional synthetic approach of the formers involves treatment of 2-aminophenol with isothiocyanates to obtain the corresponding thioureas, which later undergo a cyclodesulfurization step with the assistance of diverse desulfurizing agents.7 Reported routes to 2-aminobenzothiazoles include: i) reacting 2,2’-diaminodiphenyl disulfide with isothiocyanates,8 ii) copper(I)-catalyzed reaction of 2-iodoaniline with isothiocyanates,9 and iii) microwave promoted reaction of 2-chlorobenzothiazole with an amine.10 When an isothiocyanate is invovled as one of the starting material, the methods usually need desulfurizing agents. These desulfurizing agents are mostly converted to acidic gases, compounds with terrible odor, or heavy metals. We also notice that these methods often need longer reaction time, lead to problems with complex workup or suffer from low yields.
Because of the similarity on structural and chemical properties and especially stronger leaving tendency of selenium, we decided to develop analogous reactions with isoselenocyanates, and herein to report an efficient one-pot procedure for the synthesis of two important classes of compounds, 2-aminobenzoxazoles and 2-aminobenzothiazoles.

RESULTS AND DISCUSSION
Phenyl isoselenocyanates and cyclohexyl isoselenocyanate have been prepared following Fernández-Bolaños’s procedure.11 Equimolar amounts of a 2-aminophenol and an isoselenocyanate were then added to DMF. To our great surprise, 2-aminobenzoxazole was obtained in excellent yield and elemental Se was precipitated without any deselenizing agent. The precipitation made the post workup extremely easy: only a filtration was needed to separate Se from the mixture. The filtrate was concentrated and purified chromatographically to give 2-aminobenzoxazole. Futhermore, we optimized the reaction condition of the cyclocondensation of 2-aminophenol 2 and 1-isoselenocyanato-4- methoxybenzene 1c. The results showed that DMF is the appropriate solvent, and 70 oC was the optimal reaction temperature to give 3c in 96% yield, while lower yields were obtained in pyridine at 70 oC (82%) and in THF under reflux (81%). Other solvents such as CH2Cl2, toluene and AcOEt gave no desired product. It might due to DMF provided an alkaline condition that enhanced the attack capability of the amino group of 2-aminophenol.
Under the optimized conditions, a variety of 2-aminobenzoxazoles were prepared. As shown in Table 1, phenyl isoselenocyanates containing both electron donating and electron withdrawing groups, respectively, gave 2-aminobenzoxazoles in good to excellent yields. The effect of different substituent on the 2-aminophenol was also considered. With the strong electron withdrawing effect of the nitro group, the nucleophilic tendency of the amino group was largely reduced and the total reaction time was prolonged to 14 h. However, the precipitation of Se promoted the reaction proceeding and gave target products in good yields.

he successful preparation of 2-aminobenzoxazoles encouraged us to apply this methodology for the synthesis of 2-aminobenzothiazoles. As expected, various 2-aminobenzothiazoles were prepared successfully. A lower reaction temperature (40 °C) was needed, which might be the result of the stronger nucleophilicity of the SH group. As can be seen from Table 2, different substituents were also well tolerated in this reaction. Electron donating and electron withdrawing groups on phenyl isoselenocyanates as well as cyclohexyl isoselenocyanate performed well in this reaction and gave excellent yields.

Since a variety of 2-aminobenzoxazoles and 2-aminobenzothiazoles were prepared by this method, we were eager to know the recovery rate of Se precipitated in the reaction. With great success, the recovery rate was 95-97%, which means that Se was nearly quantitatively recovered. Isoselenocyanates could be reproduced from these selenium, thus to cut the waste to the minimum (Table 1, Entry 1; Table 2, Entry 1).
In the light of all these results, two possible reaction mechanisms are proposed in Scheme 1. In both cases, a selenourea 5 was generated by the reaction of 2-aminophenol or 2-aminothiophenol with isoselenocyanate. In path I, 5 was then converted to product 3 through an intramolecular cyclization with the assistant of O2. Another popular mechanism12 for this type of reaction shown as path II involved the formation of a carbodiimide intermediate 7, which cyclized spontaneously to give the desired product 3. An experiment under N2 atmosphere had been carried out to determine the necessity of the O2. According to our results, only selenourea 5 was formed after 36 h, which means that the reaction does not lead to 3 without the help of O2, thus supporting path I.

In summary, we have developed a novel one-pot procedure for the synthesis of 2-aminobenzoxazoles and 2-aminobenzothiazoles by reacting isoselenocyanates with 2-aminophenol or 2-aminothiophenol without using a deselenizing agent. Compared with traditional routes, this method provides a high yield of the target products with both electron-donating and electron-withdrawing groups. The reaction was performed under mild conditions, and the key material, i.e. the isoselenocyanates, could be reproduced from the precipitated elemental Se, which largely simplifies the purification procedures and minimizes the harm to the environment. The method also widens the application of isoselenocyanates as important reagents. An experiment was carried out to determine the reaction mechanism and the oxygen-involved intramolecular cyclization pathway was confirmed.

EXPERIMENTAL
General. Mp: Büchi B-540 apparatus; uncorrected. IR Spectra: Nicolet Avatar-370 spectrometer, in KBr; in cm-1. 1H- and 13C-NMR Spectra: Varian Mercury Plus-400 instrument, in (d6) DMSO at 400 and 100 MHz, resp.; δ in ppm, J in Hz. ESI-MS: Thermo Finnigan LCQ Advantage instrument; in m/z. HRMS: Agilent 6210 TOF instrument.
General Procedure for the Synthesis of 2-Aminobenzoxazoles. (Take 3a for example). Phenyl isoselenocyanate (0.182g, 1 mmol) and 2-aminophenol (0.109g, 1 mmol) were added to DMF (20 mL) with magnetic stirring. The mixture was heated to 70 oC for 6.5 h. When the reaction was completed as monitored by TLC, the mixture was cooled to rt. The solid Se was filtered off and washed with AcOEt (10 mL). The recovery rate of Se is 95% - 97%. The combined filtrate was concentrated in vacuo and the residue was chromatographed on silica gel (hexane:AcOEt = 1:1) to give white solid N-Phenylbenzo[d]oxazol-2-amine 3a (0.179 g, 85%).
General Procedure for the Synthesis of 2-Aminobenzothiazoles. (Take 3k for example). Phenyl isoselenocyanate (0.182 g, 1 mmol) and 2-aminothiophenol (0.125 g, 1 mmol) were added to DMF (20 mL) with magnetic stirring. The mixture was heated to 40 oC for 6 h. When the reaction was completed as monitored by TLC, the mixture was cooled to rt. The solid Se was filtered off and washed with AcOEt (10 mL). The combined filtrate was concentrated in vacuo and the residue was chromatographed on silica gel (hexane : AcOEt = 1 : 1) to give white solid N-phenylbenzo[d]thiazol-2-amine 3k (0.201 g, 89%).
Procedure for Control Experiment. Phenyl isoselenocyanate (0.182 g, 1 mmol) and 2-aminophenol (0.109 g, 1 mmol) were added successively to DMF (20 mL) with magnetic stirring under an N2 atmosphere. The mixture was heated to 70 oC and monitored by TLC. The reaction time was prolonged to 36 h, no product 3a was detected.


N-Phenylbenzo[d]oxazol-2-amine (3a; Table 2).
White solid. Mp 176.6–177.1 oC. Lit.,12 mp 176–178 oC. IR (KBr): 3379, 3154, 3105, 3039, 1928, 1662, 1572, 1490, 1282, 1217, 971, 738, 681 cm-1. 1H-NMR (400 MHz, DMSO-d6): 10.62 (s, 1H); 7.77(d, J = 8.4, 2H); 7.45-7.50 (m, 2H); 7.38 (t, J = 8.4, 2H ); 7.23 (t, J =8.4, 1H); 7.14 (t, J = 7.2, 1H); 7.04 (t, J = 7.2, 1H). 13C-NMR (400 MHz, DMSO-d6): 157.9 (s); 147.0 (s); 142.4 (s); 138.74 (s); 128.9 (2×CH); 123.9 (d); 122.1 (d); 121.6 (d); 117.5 (2×CH); 116.6 (d); 108.9 (d). ESI-MS: 211 (M-H) -.

N-(4-Methylphenyl)benzo[d]oxazol-2-amine (3b; Table 2).
White solid. Mp 172.3–172.8 oC. Lit.,13 mp 169–171 oC. IR (KBr): 3382, 3161, 1664, 1574, 1460, 1401, 1227, 820, 737 cm-1. 1H-NMR (400 MHz, DMSO-d6): 10.50 (s, 1H); 7.64 (d, J = 8.4, 2H); 7.43-7.48(m, 2H); 7.17-7.23 (m, 3H); 7.12 (t, J = 7.2 , 1H); 2.28 (s, 3H). 13C-NMR (400 MHz, DMSO-d6): 158.1 (s); 147.0 (s); 142.5 (s); 136.2 (s); 131.0 (s); 129.3 (2×CH); 123.9 (d); 121.5 (d); 117.6 (2×CH); 116.4 (d); 108.8 (d); 20.3(q). ESI-MS: 225 (M-H)-.

N-(4-Methoxyphenyl)benzo[d]oxazol-2-amine (3c; Table 2).
White solid. Mp 135.4–136.5 oC. Lit.,12 mp 136–138 oC. IR (KBr): 3383, 2994, 2839, 1675, 1581, 1512, 1460, 1232, 1033, 822, 742 cm-1. 1H-NMR (400 MHz, DMSO-d6): 10.41 (s, 1H); 7.68 (d, J = 8.0, 2H); 7.42-7.47 (m, 2H); 7.21 (t, J = 7.2, 1H); 7.10 (t, J = 7.2, 1H); 6.97 (d, J = 9.2, 2H); 3.75 (s, 3H). 13C-NMR (400 MHz, DMSO-d6): 159.4 (s); 156.1 (s); 147.9 (s); 142.1 (s); 131.0 (s); 124.2 (d); 121.4 (d), 121.1 (2×CH); 116.5 (d); 114.5 (2×CH); 109.1 (d); 55.5 (q). ESI-MS: 241 (M-H) -.

N-(4-Chlorophenyl)benzo[d]oxazol-2-amine (3d; Table 2).
White solid. Mp 153.1–154.5 oC. IR (KBr): 3428, 3157, 1663, 1575, 1491, 1400, 1230, 738 cm-1. 1H-NMR (400 MHz, DMSO-d6): 10.79 (s, 1H); 7.79 (d, J = 8.4, 2H); 7.46-7.52 (m, 2H); 7.44 (d, J = 8.4, 2H); 7.24 (t, J = 7.2, 1H); 7.15 (t, J = 7.2, 1H). 13C-NMR (400 MHz, DMSO-d6): 157.7 (s); 147.0 (s); 142.2 (s); 137.7 (s); 128.9 (2×CH); 125.7 (s); 124.1 (d); 121.9 (d); 119.1 (2×CH); 116.7 (d); 109.1 (d). ESI-MS: 245(M-H)- ; 247 (M+2-H)-.

5-Nitro-N-phenylbenzo[d]oxazol-2-amine (3e; Table 2).
Yellow solid. Mp 238.5–239.4 oC. Lit.,13 mp 236 oC. IR (KBr): 3109, 3041, 2882, 1720, 1601, 1530, 1336, 1266, 978, 875, 813, 734 cm-1. 1H-NMR (400 MHz, DMSO-d6): 11.04 (s, 1H), 8.24 (d, J = 2.4, 1H); 8.08 (dd, J = 2.4, 8.8, 1H); 7.72-7.77 (m, 3H); 7.42 (t, J = 7.6, 2H); 7.10 (t, J = 7.6, 1 H). 13C-NMR (400 MHz, DMSO-d6): 160.0 (s); 151.3 (s); 144.5 (s); 143.3 (s); 137.9 (s); 128.9 (2×CH); 122.8 (d); 118.1 (3×CH); 111.4 (d); 109.1 (d). ESI-MS: 256 (M+H)+.

5-Nitro-N-(2-methylphenyl)benzo[d]oxazol-2-amine (3f; Table 2).
Yellow solid. Mp 171.2–172.1 oC. IR (KBr): 3419, 1663, 1598, 1525, 1463, 1346, 1274, 1241, 877, 737 cm-1. 1H-NMR (400 MHz, DMSO-d6): 10.17 (s, 1H); 8.13 (s, 1H); 8.03-8.06 (m, 1H); 7.68-7.72 (m, 2H); 7.28 (t, J = 8.0, 2H); 7.16 (t, J = 7.2, 1H); 2.31 (s, 3H). 13C-NMR (400 MHz, DMSO-d6): 161.8 (s); 151.9 (s); 144.5 (s); 143.6 (s); 135.7 (d); 131.3 (s); 130.6 (s); 126.5 (d); 125.4 (d); 123.8 (d); 117.6 (d); 111.1 (d); 109.1 (d); 17.7 (q). HRMS: calcd for C14H10N3O3: 268.0722; found: 268.0730.

N-(4-Methoxyphenyl)-5-nitrobenzo[d]oxazol-2-amine (3g; Table 2).
Yellow solid. Mp 203.2–204.7 oC. IR (KBr): 3400, 3114, 1672, 1584, 1524, 1511, 1345, 1248, 878, 818, 739 cm-1. 1H-NMR (400 MHz, DMSO-d6): 10.83 (s, 1H); 8.20 (d, J = 2.4, 1H); 8.06 (dd, J = 2.4, 8.8, 1H); 7.70 (d, J = 8.8, 1H); 7.65 (d, J = 9.2, 2H); 6.99 (d, J = 9.2, 2H); 3.76 (s, 3H). 13C-NMR (400 MHz, DMSO-d6): 160.4 (s); 155.2 (s); 151.5 (s); 144.5 (s); 143.6 (s); 131.0 (s); 119.8 (2×CH); 117.8 (d); 114.3 (2×CH); 111.1 (d); 109.0 (d); 55.2 (q). HRMS: calcd for C14H10N3O4: 284.0671; found: 284.0684.

5-Chloro-N-phenylbenzo[d]oxazol-2-amine (3h; Table 2).
Grey solid. Mp 203.4–204.9 oC. Lit.,14 mp 212–213 oC. IR (KBr): 3481, 3414, 3124, 1679, 1618, 1577, 1446, 1401, 1230, 980, 788 cm-1. 1H-NMR (400 MHz, DMSO-d6): 10.79 (s, 1H); 7.73-7.75 (m, 2 H); 7.51-7.53 (m, 2H); 7.37-7.41 (m, 2H); 7.16 (dd, J = 2.0, 8.4, 1H); 7.06 (t, J = 7.6, 1 H). 13C-NMR (400 MHz, DMSO-d6): 159.1 (s); 145.8 (s); 144.0 (s); 138.3 (s); 128.9 (2×CH); 128.1 (s); 122.4 (d); 121.2 (d); 117.8 (2×CH); 116.2 (d); 110.0 (d). ESI-MS: 243 (M-H)- ; 245 (M+2-H)-.

5-Chloro-N-(2-methylphenyl)benzo[d]oxazol-2-amine (3i; Table 2).
White solid. Mp 195.3–196.4 oC. IR (KBr): 3128, 3028, 2893, 1660, 1577, 1459, 1358, 1236, 1191, 972, 846, 763 cm-1. 1H-NMR (400 MHz, DMSO-d6): 9.88 (s, 1H); 7.73-7.75 (m, 1H); 7.47 (d, J = 8.4, 1H); 7.41 (d, J = 2.4, 1H); 7.26 (t, J = 7.2, 2H); 7.10-7.14 (m, 2H); 2.30 (s, 3H). 13C-NMR (400 MHz, DMSO-d6): 160.8 (s); 146.4 (s); 144.2 (s); 136.1 (s); 130.8 (s); 130.5 (d); 128.0 (s); 126.4 (d); 124.9 (d); 123.3 (d); 120.7 (d); 115.9 (d); 109.9 (d); 17.7 (q). HRMS: calcd for C14H10ClN2O: 257.0482; found: 257.0489.

5-Chloro-N-(4-methoxyphenyl)benzo[d]oxazol-2-amine (3j; Table 2).
White solid. Mp 182.3–182.9 oC. IR (KBr): 3148, 3006, 2936, 1689, 1578, 1513, 1492, 1462, 1259, 1035, 972, 829, 794 cm-1. 1H-NMR (400 MHz, DMSO-d6): 10.56 (s, 1H); 7.63 (d, J = 8.8, 2H); 7.46-7.49 (m, 2H), 7.12 (dd, J = 2.4, 8.4, 1H); 6.97 (d, J = 7.2, 2H); 3.75 (s, 3H). 13C-NMR (400 MHz, DMSO-d6): 159.5 (s); 154.9 (s); 145.9 (s); 144.2 (s), 131.4 (s); 128.0 (s); 120.9 (d); 119.5 (2×CH); 116.0 (d); 114.2 (2×CH); 109.8 (d); 55.2 (q). ESI-MS: 273 (M-H)- ; 275 (M+2-H)-.

N-Phenylbenzo[d]thiazol-2-amine (3k; Table 3).
White solid. Mp 160.4–161.5 oC. Lit.,15 mp 160–162 oC. IR (KBr): 3422, 3189, 3129, 3053, 2936, 1626, 1573, 1467, 1447, 1249, 922, 745, 721 cm-1. 1H-NMR (400 MHz, DMSO-d6): 10.48 (s, 1H); 7.79-7.82 (m, 3H); 7.61 (d, J = 8.4, 1H); 7.31-7.39 (m, 3H); 7.16 (t, J = 7.2, 1H), 7.03 (t, J = 7.2, 1H). 13C-NMR (400 MHz, DMSO-d6): 161.6 (s); 152.1 (s); 140.6 (s); 130.0 (s); 129.0 (2×CH), 125.9 (d); 122.3 (d); 122.0 (d);
121.1 (d); 119.2 (d); 117.7 (2×CH). ESI-MS: 227 (M+H)+.

N-(3-Methylphenyl)benzo[d]thiazol-2-amine (3l; Table 3).
White solid. Mp 120.3–121.1 oC. Lit.,16 mp 124 oC. IR (KBr): 3447, 2922, 1626, 1575, 1448, 1276, 1250, 746, 721 cm-1. 1H-NMR (400 MHz, DMSO-d6): 10.40 (s, 1H); 7.80 (d, J = 8.0, 1H); 7.56-7.65 (m, 3H); 7.33 (t, J = 7.2, 1H); 7.25 (t, J = 7.6, 1H); 7.16 (t, J = 8.0, 1H); 6.85 (d, J = 7.6, 1H); 2.33 (s, 3H). 13C-NMR (400 MHz, DMSO-d6): 161.6 (s); 152.1 (s); 140.6 (s); 138.2 (d); 130.0 (s); 128.9 (d); 125.9 (d); 122.9 (d); 122.2 (d); 121.0 (d); 119.2 (s); 118.3 (d); 115.1 (d); 21.3 (q). ESI-MS: 241 (M+H)+.

N-(2-Ethylphenyl)benzo[d]thiazol-2-amine (3m; Table 3).
White solid. Mp 152.5–153.9 oC. IR (KBr): 3446, 3176, 2964, 2868, 1612, 1595, 1562, 1446, 1265, 1018, 752, 725 cm-1. 1H-NMR (400 MHz, DMSO-d6): 9.69 (s, 1H); 7.72-7.76 (m, 2H); 7.46 (d, J = 7.6, 1H); 7.24-7.30 (m, 3H); 7.15-7.19 (m, 1H); 7.07-7.11 (m, 1 H); 2.69 (q, J = 7.6, 2H); 1.14 (t, J = 7.6, 3H). 13C-NMR (400 MHz, DMSO-d6): 164.9 (s); 152.0 (s); 138.1 (s); 137.2 (d); 130.2 (s); 129.0 (d); 126.6 (d); 125.7 (d); 125.4 (d); 124.5 (d); 121.6 (d); 121.0 (d); 118.5 (s); 23.9 (t); 14.4 (q). ESI-MS: 255 (M+H)+.

N-(4-Methoxyphenyl)benzo[d]thiazol-2-amine (3n; Table 3).
White solid. Mp 161.4–162.5 oC. Lit.,17 mp 158–160 oC. IR (KBr): 3445, 2836, 1620, 1572, 1511, 1453, 1232, 1037, 826, 745 cm-1. 1H-NMR (400 MHz, DMSO-d6): 10.29 (s, 1H); 7.77 (d, J = 7.6, 1H); 7.69 (d, J = 8.8, 2H); 7.55 (d, J = 7.6, 1H); 7.31(t, J = 7.6, 1H); 7.12 (t, J = 7.6, 1H), 6.96 (d, J = 8.8, 2H); 3.75 (s, 3H). 13C-NMR (400 MHz, DMSO-d6): 162.0 (s); 154.6 (s); 152.3 (s); 134.0 (s); 129.9 (s); 125.8 (d); 121.9 (d); 121.0 (d); 119.6 (2×CH); 118.9 (d); 114.2 (2×CH); 55.2 (q). ESI-MS: 257 (M+H)+.

N-(4-Chlorophenyl)benzo[d]thiazol-2-amine (3o; Table 3).
White solid. Mp 194.5–195.2 oC. Lit.,18 mp 195–196 oC. IR (KBr): 3445, 3170, 3065, 2845, 1609, 1561, 1448, 1269, 1216, 1056, 918, 841, 751 cm-1. 1H-NMR (400 MHz, DMSO-d6): 10.08 (s, 1H); 8.33 (d, J = 8.0, 1H); 7.82 (d, J = 7.6, 1H); 7.58 (d, J = 8.4, 1H); 7.53 (dd, J = 1.2, 8.0, 1H); 7.41 (td, J = 1.2, 8.0, 1H); 7.33 (td, J = 1.2, 8.0, 1H); 7.13-7.19 (m, 2H). 13C-NMR (400 MHz, DMSO-d6): 162.8 (s); 151.1 (s); 137.4 (s); 129.7 (s); 127.8 (2×CH); 125.8 (d); 124.8 (d); 124.3 (s); 123.4 (2×CH); 122.3 (d); 121.1 (d). ESI-MS: 259 (M-H)- ; 261 (M+2-H)-.

N-Cyclohexylbenzo[d]thiazol-2-amine (3p; Table 3).
White solid. Mp 103.1 - 104.5 oC. Lit.,19 mp 103–104 oC. IR (KBr): 3456, 2929, 2852, 1608, 1567, 1445, 1365, 1275, 885, 752 cm-1. 1H-NMR (400 MHz, DMSO-d6): 7.94 (d, J = 7.6, 1H); 7.63 (d, J = 8.0, 1H); 7.37 (d, J = 8.0, 1H); 7.19 (t, J = 7.6, 1H); 6.99 (t, J = 7.6, 1H); 3.68 v 3.72 (m, 1H), 1.97–2.00 (m, 2H), 1.70-1.75 (m, 2H); 1.56-1.60 (m, 1H); 1.17-1.38 (m, 5H). 13C-NMR (400 MHz, DMSO-d6): 165.1 (s); 152.8 (s); 130.1 (s); 125.4 (d); 120.7 (d); 120.6 (d); 117.8 (d); 52.7 (d); 32.3 (2×CH2); 25.3 (t); 24.4
(2×CH2). ESI-MS: 233 (M+H)+.

1-(2-hydroxyphenyl)-3-phenylselenourea (5a).
Pink solid. Mp 153–155 oC. IR (KBr): 3302, 3186, 3114, 2932, 1600, 1546, 1492 cm-1. 1H-NMR (400 MHz, DMSO-d6): 9.99 (s, 1H); 9.77 (s, 1H); 9.42 (s, 1H); 7.59 (d, J = 7.6 Hz, 1H); 7.43 (d, J = 7.6 Hz, 2H); 7.32 (t, J = 7.6 Hz, 2H); 7.16 (t, J = 7.6 Hz, 1H); 7.03 (t, J = 8.0 Hz, 1H); 6.86 (d, J = 8.0 Hz, 1H); 6.76 (t, J = 7.6 Hz, 1H). 13C-NMR (400 MHz, DMSO-d6): 177.7 (s); 150.7 (s); 139.4 (s); 128.4 (2×CH); 126.9 (d); 126.7 (d); 126.5 (s); 125.2 (d); 124.8 (2×CH); 118.5 (d); 115.8 (d). ESI-MS: 291 (M-H)-. HRMS: calcd for C13H11N2OSe: 291.0037; found: .291.0041

ACKNOWLEDGEMENTS
We are grateful to the National Natural Science Foundation of China (No 20906083 and No 20806073) and Natural Science Foundation of Zhejiang Province (No Y40900488) for financial support.

References

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