Abstract

2-Amino-4,5-diphenylfuran-3-carbonitrile 1 was utilized as building block for the construction of new furo[2,3-d]pyrimidin-4(3H)-one derivative 2 and 4H-furo2,3-d1,3oxazin-4-one derivative 3 via treatment with acetic anhydride and benzoyl chloride, respectively. The 4H-furo2,3-d1,3oxazin-4-one derivative 3 was transformed into novel furo[2,3-d]pyrimidin-4(3H)-ones 48, tetrazolylfuran derivative 10, and furo[3,2-d]imadazolone derivative 11 via reaction with various nitrogen nucleophiles. The structure features of the synthesized compounds were established from their spectral and elemental analyses.

1. Introduction

Substituted and fused furans are one of the most important scaffolds in medicinal chemistry due to owning various biological activities including antimicrobial, antitumor, antiviral, antidepressant, and antihistaminic effects [1]. On the other hand, pyrimidines and fused pyrimidines represent an important class of heterocyclic compounds due to their biological activities [27]. Among the fused pyrimidines, the furopyrimidines attract the attention of the chemists due to possessing broad scope of pharmaceutical activities such as anticancer [8, 9], antiviral [10, 11], and antimicrobial [12] activities. There are great numbers of synthetic strategies for the preparation of furo2,3-dpyrimidines [10, 1320]. Substituted 2-aminofuran-3-carbonitriles are known as easily obtainable starting material for synthesis of furo2,3-dpyrimidines using different reagents [1316]. In the context of our sustained efforts to construct fused oxazine systems [2123] and other heterocycles with potent antimicrobial activities [2427], herein we reported the utility of 2-amino-4,5-diphenylfuran-3-carbonitrile [28] in synthesis of furo2,3-d1,3oxazin-4-one and its transformation into different furo2,3-dpyrimidines and other heterocyclic systems via reactions with different nitrogen nucleophiles.

2. Experimental

Melting points were recorded on a Gallenkamp melting point apparatus. The FTIR spectra were run on a Pye Unicam SP 3-300 spectrometer. 1H-NMR spectra were recorded on a JEOL ECA-500 (300 MHz) spectrometer; chemical shifts were expressed in part per million (ppm) against TMS as an internal standard. 13C-NMR spectra were run at 75.46 MHz. The MS spectra were measured on Agilent 5977A/MSD mass spectrometers (Agilent Technologies, USA) at 70 eV. Elemental analysis was performed by Vario EL-III elemental analysis.

2.1. 2,5,6-Triphenylfuro[2,3-d]pyrimidin-4(3H)-one 2

A mixture of amino carbonitrile 1 (3 g, 10 mmol) and benzoyl chloride (30 mL) was refluxed for 24 hrs. The excess solvent was distilled off and the remaining solid was crystallized from benzene to give 2 as brown crystals, m.p. 122–124°C, yield 49%. Anal. Calcd. for C24H16N2O2 (364.388): C, 79.11; H, 4.42; N, 7.69. Found: C, 79.07; H, 4.45; N, 7.65. IR (KBr, ν cm−1): 3169 (NH), 1687 (CO). 1H-NMR (DMSO-d6) (ppm): 12.93 (s, 1H NH, exchangeable by D2O), 7.92–7.44 (m, 15H, Ar-H); 13C-NMR (DMSO-d6) δ (ppm): 167.87, 133.50, 130.99, 129.78, 129.12. MS m/z (%): 364 (M+, 100), 345 (10), 204 (9), 128 (15), 122 (18), 105 (42), 77 (40).

2.2. 2-Methyl-5,6-diphenyl-4H-furo[2,3-d][1,3]oxazin-4-one 3

A solution of amino carbonitrile 1 (3 g, 10 mmol) and freshly distilled acetic anhydride (30 mL) was heated under reflux for 24 hrs. The excess of acetic anhydride was removed and the remaining solid was crystallized from benzene to give 3 as gray crystals, m.p. 196–198°C, yield 55%. Anal. Calcd. for C19H13NO3 (303.303): C, 75.24; H, 4.32; N, 4.62. Found: C, 75.20; H, 4.30; N, 4.65. IR (KBr, ν cm−1): 1773 (CO). 1H-NMR (DMSO-d6) δ (ppm): 7.70–7.00 (m, 10H, Ar-H), 2.4 (s, 3H, CH3); 13C- NMR (DMSO-d6) δ (ppm): 167.68, 163.56, 156.18, 146.88, 145.68, 130.27, 129.44, 129.26, 129.16, 129.03, 128.83, 126.82, 21.90. MS m/z (%): 303 (M+, 100), 261 (96), 204 (18), 178 (14), 128 (28), 105 (31), 77 (33).

2.3. 3-Amino-2-methyl-5,6-diphenylfuro[2,3-d]pyrimidin-4-one 4

A mixture of furo2,3-d1,3oxazinone 3 (1.5 g, 5 mmol) and hydrazine hydrate (0.25 mL, 5 mmol) was stirred at room temperature in absolute ethanol (30 mL) for 30 min. The solid produced was filtered off, dried, and then crystallized from dioxane to afford 4 as pale yellow crystals, m.p. 212–214°C, yield 87%. Anal. Calcd. for C19H15N3O2 (317.330): C, 71.92; H, 4.76; N, 13.24. Found: C, 71.95; H, 4.80; N, 13.27. IR (KBr, ν cm−1): 3308, 3256 (NH2), 1691 (CO). 1H-NMR (DMSO-d6) δ (ppm): 7.75–7.30 (m, 10H, Ar-H), 5.79 (s, 2H, NH2, exchangeable by D2O), 2.4 (s, 3H, CH3). 13C-NMR (DMSO-d6) δ (ppm): 161.76, 157.64, 157.48, 146.27, 131.10, 130.50, 129.50, 129.31, 128.92, 128.66, 126.72, 104.95, 22.45. MS m/z (%): 317 (M+, 100), 260 (9), 184 (15), 178 (4), 128 (4), 105 (13), 77 (12).

2.4. 2-Methyl-5,6-diphenylfuro[2,3-d]pyrimidin-4-one 5

A mixture of furo2,3-d1,3oxazinone 3 (1.5 g, 5 mmol) in formamide (15 mL) was refluxed for 3 hrs. The reaction mixture, after cooling, was poured into ice/cold water and the separated solid was filtered off, dried, and crystallized from benzene to give 5, as pale yellow crystals, m.p. 225-226°C, yield 75%. Anal. Calcd. for C19H14N2O2 (302.317): C, 75.53; H, 4.67; N, 9.27. Found: C, 75.51; H, 4.64; N, 9.30. IR (KBr, ν cm−1): 3474, (NH), 1676 (CO). 1H-NMR (DMSO-d6) δ (ppm): 12.63 (s, 1H, NH, exchangeable by D2O), 7.50–7.29 (m, 10H, Ar-H), 2.4 (s, 3H, CH3); 13C-NMR (DMSO-d6) (ppm): 161.40, 151.96, 148.31, 129.95, 129.43, 129.25, 128.86, 74.51, 22.45. MS m/z (%): 302 (M+, 3), 288 (9), 271 (100), 256 (14), 216 (9), 189 (13), 105 (3), 77 (6).

2.5. 3-Hydroxy-2-methyl-5,6-diphenylfuro[2,3-d]pyrimidin-4-one 6

A solution of furo2,3-d1,3oxazin-4-one 3 (1.5 g, 5 mmol) and hydroxylamine hydrochloride (0.34 g, 5 mmol) in pyridine (10 mL) was heated under reflux for 3 hrs. The reaction mixture was allowed to cool and then poured into ice/HCl. The obtained solid was filtered off, dried, and crystallized from benzene to give 6 as pale yellow crystals, m.p. 70–72°C, yield 77%. Anal. Calcd. for C19H14N2O3 (318.316): C, 71.69; H, 4.43; N, 8.80. Found: C, 71.65; H, 4.40; N, 8.83. IR (KBr, ν cm−1): 3412, (br, OH), 1670 (CO). 1H-NMR (DMSO-d6) δ (ppm): 8.02–7.20 (m, 10H, Ar-H), 7.36 (s, 1H, OH, exchangeable by D2O), 2.46 (s, 3H, CH3); 13C-NMR (DMSO-d6) δ (ppm): 167.19, 137.99, 134.21, 129.74, 129.40, 129.25, 128.54, 128.27, 49.91, 22.40. MS m/z (%): 318 (M+, 3), 317 (13), 286 (19), 271 (21), 236 (38), 231 (20), 189 (11), 105 (100), 77 (51).

2.6. 1-(2-Methyl-4-oxo-5,6-diphenylfuro[2,3-d]pyrimidin-3(4H)-yl)thiourea 7

A mixture of furo2,3-d1,3oxazinone 3 (1.5 g, 5 mmol), thiosemicarbazide (0.45 g, 5 mmol), and acetic acid (15 mL) was heated under reflux for 4 hrs. The reaction mixture was concentrated and poured into ice/cold water. The formed solid was filtered off, washed with water, dried, and then crystallized from toluene to give 7 as violet crystals, m.p. 168–170°C, yield 50%. Anal. Calcd. for C20H16N4O2S (376.420): C, 63.82; H, 4.28; N, 14.88; S, 8.52. Found: C, 63.78; H, 4.32; N, 14.85; S, 8.55. IR (KBr, ν cm−1): 3377, 3360, 3290 (NH, NH2), 1672 (CO), 1179 (C=S). 1H-NMR (DMSO-d6) δ (ppm): 10.63 (s, 1H, NH, exchangeable by D2O), 9.50 (s, 2H, NH2, exchangeable by D2O), 7.60–7.29 (m, 10H, Ar-H), 2.25 (s, 3H, CH3). MS m/z (%): 376 (M+, 1), 304 (22), 303 (100), 261 (94), 204 (16), 178 (14), 128 (27), 105 (44), 77 (39).

2.7. 2-Methyl-5,6-diphenyl-3-p-tolylfuro[2,3-d]pyrimidin-4(3H)-one 8

A mixture of furo2,3-d1,3oxazinone 3 (1.5 g, 5 mmol), p-toluidine (0.53 g, 10 mmol), and n-butanol (15 mL) was heated under reflux for 3 hrs. The reaction mixture was concentrated and the solid formed after cooling was filtered off, dried, and then crystallized from ethanol to afford 8 as brown crystals, m.p. 160–162°C, yield 50%. Anal. Calcd. for C26H20N2O2 (392.436): C, 79.58; H, 5.13; N, 7.14. Found: C, 79.53; H, 5.16; N, 7.14. IR (KBr, ν cm−1): 1698 (CO). 1H-NMR (DMSO-d6) δ (ppm): 7.67–7.04 (m, 14H, Ar-H), 2.46 (s, 3H, CH3). MS m/z (%): 392 (M+, 8), 373 (12), 368 (22), 337 (21), 302 (100), 261 (30), 206 (14), 178 (15), 128, (27), 105 (71), 77 (47).

2.8. 2-Acetamido-N-(4-aminophenyl)-4,5-diphenylfuran-3-carboxamide 9

A mixture of furo2,3-d1,3oxazinone 3 (1.5 g, 5 mmol), p-phenylenediamine (0.54 g, 5 mmol), and dioxane (15 mL) was heated under reflux for 3 hrs. The reaction mixture was concentrated and the solid formed after cooling was filtered off, dried, and then crystallized from ethanol to afford 9 as yellow crystals, m.p. 200–202°C, yield 60%. Anal. Calcd. for C25H21N3O3 (411.437): C, 72.98; H, 5.14; N, 10.21. Found: C, 73.02; H, 5.16; N, 10.17. IR (KBr, ν cm−1): 3401, 3324 (2NH), 1699 (br, CO). 1H-NMR (DMSO-d6) δ (ppm): 12.07 (s, 1H, NH, exchangeable by D2O), 9.77 (s, 1H, NH, exchangeable by D2O), 7.33–7.14 (m, 14H, Ar-H), 5.09 (s, 2H, NH2 exchangeable by D2O), 2.46 (s, 3H, CH3). 13C-NMR (DMSO-d6) δ (ppm): 163.55, 159.53, 146.92, 141.72, 133.84, 130.60, 130.46, 128.97, 128.66, 127.89, 127.32, 125.10, 124.65, 123.23, 114.36, 101.78, 66.89, 21.28. MS m/z (%): 411 (M+, 2), 337 (14), 302 (100), 261 (10), 189 (13), 178 (10), 128, (21), 105 (74), 77 (42).

2.9. Procedure for Preparation of 10 and 11

A mixture of furo2,3-d1,3oxazinone 3 (1.5 g, 5 mmol) and sodium azide (0.65 g, 5 mmol) in glacial acetic acid (15 mL) was heated under reflux for 3 hrs. The reaction mixture was allowed to cool and then poured onto ice/cold water and the separated solid was filtered, washed with water, and dried. Fractional crystallization from ethanol gave tetrazole derivative 10 and the insoluble fraction was crystallized from dioxane to yield the imidazolone derivative 11.

2.9.1. 2-(5-Methyl-1H-tetrazol-1-yl)-4,5-diphenylfuran-3-carboxylic acid 10

White crystals; m.p. > 300°C, yield 35%. Anal. Calcd. for C19H14N4O3 (346.328): C, 65.89; H, 4.07; N, 16.18. Found: C, 65.92; H, 4.05; N, 16.14. IR (KBr, ν cm−1): 3431 (br, OH, acid), 1669 (CO, acid). 1H NMR (DMSO-d6) δ (ppm): 11.25 (s, 1H, COOH, exchangeable by D2O), 8.20–7.35 (m, 10H, Ar-H), 2.14 (s, 3H, CH3). MS m/z (%): 346 (M+, 30), 301 (100), 273 (25), 128 (13), 105 (65), 77 (50).

2.9.2. 3-Acetyl-5,6-diphenyl-1H-furo[3,2-d]imidazol-2(3H)-one 11

Pale yellow crystals; m.p. > 300°C, yield 65%. Anal. Calcd. for C19H14N2O3 (318.316): C, 71.69; H, 4.43; N, 8.80. Found: C, 71.66; H, 4.46; N, 8.84. IR (KBr, ν cm−1): 3262 (NH), 1746, 1668 (2CO). 1H NMR (DMSO-d6) δ (ppm): 11.98 (s, 1H, NH, exchangeable by D2O), 7.95–7.06 (m, 10H, Ar-H), 2.45 (s, 3H, CH3). MS m/z (%): 318 (M+, 26), 303 (70), 275 (100), 128 (30), 105 (78), 77 (45).

3. Results and Discussion

2-Amino-4,5-diphenylfuran-3-carbonitrile 1 [28] was used as precursor for the preparation of the target heterocyclic compounds. Thus, benzoylation of 1 using benzoyl chloride afforded 2,5,6-triphenylfuro2,3-dpyrimidin-4(3H)-one 2 as a sole product. The IR spectrum of 2 showed strong absorption bands at 3169 and 1687 cm−1 corresponding to NH and CO groups, respectively. Moreover, the 1H-NMR spectrum of 2 exhibited a singlet (exchangeable by D2O) at δ 12.93 attributed to NH group. 13C-NMR spectrum of 2 displayed signals at δ of 167.87 ppm corresponding to CO of pyrimidinone ring. Formation of furo2,3-dpyrimidinone 2 is believed to proceed via benzoylation of the amino group and conversion of cyano group to the amide group, followed by 1,6-exo-trig cyclization of the amino group to the carbonyl group as formulated in Scheme 1. On the other hand, by treatment of 2-amino-4,5-diphenylfuran-3-carbonitrile 1 with freshly distilled acetic anhydride for 24 hours, the desired furo2,3-d1,3oxazin-4-one 3 was formed via acetylation of the amino group and complete hydrolysis of cyano group to the acid group, followed by 1,6-exo-trig cyclization of enolated carbonyl group to acid group (Scheme 1). IR spectrum of 3 displayed absorption band at 1773 cm−1 characteristic for CO group of oxazine ring; additionally, 13C-NMR spectrum of 3 showed signals at δ 167.68 and 21.90 ppm corresponding to CO of oxazine ring and CH3, respectively.

Oxazinone ring is very reactive semiacid anhydride ring and can be transformed into pyrimidinone ring via reaction with various nitrogen nucleophiles. Thus, stirring furo2,3-d1,3oxazin-4-one 3 with hydrazine hydrate in ethanol yielded 3-amino-2-methyl-5,6-diphenylfuro2,3-dpyrimidin-4-one 4 (Scheme 2). IR spectrum of 4 exhibited absorption bands at 3308, 3256, and 1691 cm−1 due to NH2 and CO groups and 1H-NMR (DMSO-d6) showed signal at δ 5.79 ppm which disappeared by D2O, confirming the presence of NH2 group; also 13C-NMR spectrum of 4 revealed signal at δ 161.76 ppm due to CO of pyrimidinone ring. On the other hand, boiling furo2,3-d1,3oxazin-4-one 3 with formamide afforded furo2,3-dpyrimidin-4-one derivative 5 (Scheme 2). Furthermore, furo2,3-dpyrimidin-4-one derivative 6 was obtained on reacting hydroxylamine hydrochloride and furo2,3-d1,3oxazin-4-one 3 (Scheme 2). Spectral data supported the proposed structure 6 as IR spectrum exhibited bands at 3412 cm−1 (br, OH) and 1670 cm−1 (CO); also 1H-NMR (DMSO-d6) showed the appearance of band at δ 7.36 ppm which disappeared by D2O, indicating the presence of OH group. Additionally, 13C-NMR spectrum of 6 exhibited signal at δ 167.19 ppm due to CO of pyrimidinone ring. Refluxing compound 3 with thiosemicarbazide in acetic acid for 4 hours yielded the thiourea derivative 7 (Scheme 2).

On the other hand, when furo2,3-d1,3oxazin-4-one 3 was allowed to react with p-toluidine in refluxing n-butanol the corresponding furo2,3-dpyrimidin-4-one derivative 8 was produced (Scheme 3). On the contrary, the reaction of 3 with p-phenylenediamine in boiling dioxane yielded the furancarboxamide derivative 9, whose structure was deduced from spectral and analytical data (Scheme 3). 1H-NMR spectrum revealed signals at δ 12.07 (s, 1H, NH, exchangeable by D2O), 9.77 (s, 1H, NH, exchangeable by D2O), 7.33–7.14 (m, 14H, Ar-H), 5.09 (s, 2H, NH2 exchangeable by D2O), and 2.46 (s, 3H, CH3). Moreover, 13C-NMR spectrum of 9 exhibited two signals at δ 163.55 and 159.53 ppm representing C=O of CH3CONH and C=O of CONHAr, respectively.

Reaction of furo2,3-d1,3oxazinone 3 with sodium azide in boiling acetic acid furnished two products separated by fractional crystallization: tetrazolylfuran derivative 10 which was crystallized from ethanol and furo3,2-dimidazolone derivative 11 which was crystallized from dioxane (Scheme 3). Anomalous heteroring opening of oxazinone by azide was supposed to occur via nucleophilic attack of azide either at C-2 of oxazinone ring followed by ring opening and addition of azido group on cyano group to yield tetrazolylfuran derivative 10 or at C-4 of oxazinone followed by Curtius’s rearrangement to isocyanate intermediate and then cyclization to give furo3,2-dimidazolone derivative 11 as summarized at Scheme 4.

4. Conclusion

A new series of furo2,3-dpyrimidin-4(3H)-one derivatives, 4H-furo2,3-d1,3oxazin-4-one and heterosubstituted furan, has been synthesized and their chemical structures were confirmed by different spectral and elemental analyses. Similar to related compounds, the synthesized compounds are expected to have anticipated pharmaceutical and biological potentiality.

Conflicts of Interest

The authors declare that there are no conflicts of interest regarding the publication of this paper.