Synlett 2009(4): 599-602  
DOI: 10.1055/s-0028-1087920
LETTER
© Georg Thieme Verlag Stuttgart ˙ New York

Oxidation of Biginelli Reaction Products: Synthesis of 2-Unsubstituted 1,4-Dihydropyrimidines, Pyrimidines, and 2-Hydroxypyrimidines

Sam Sik Kima, Bo Seung Choia, Jae Hoon Leea, Ki Kon Leea, Tae Hee Leea, Young Ho Kimb, Hyunik Shin*a
a Chemical Development Division, LG Life Sciences, Ltd./R&D, 104-1, Moonji-dong, Yusong-gu, Daejon 305-380, Korea
Fax: +82(42)8665754; e-Mail: hisin@lgls.com;
b Department of Fine Chemical Engineering & Applied Chemistry, BK21-E2M, Chungnam National University, Daejeon 305-764, Korea
Further Information

Publication History

Received 28 October 2008
Publication Date:
16 February 2009 (online)

Abstract

We have devised a new route toward 2-unsubstituted pyrimidine derivatives from the Biginelli product, dihydropyrimidin-2(1H)-thiones in two steps: Oxidation of dihydropyrimidin-2(1H)-thiones using oxone on wet alumina or hydrogen peroxide in the presence of catalytic amount of vanadyl sulfate provided 1,4-di­hydropyrimidine, which was further oxidized to 2-unsubstituted ­pyrimidines by the treatment of KMnO4. Oxidation of dihydropyrimidin-2(1H)-ones by KMnO4 formed 2-hydroxypyrimidine in excellent yield, whereas attempted direct desulfurative aromatization of dihydropyrimidin-2(1H)-thiones by KMnO4 resulted in the formation of 2-hydroxypyrimidines, the same products obtained in the oxidation of dihydropyrimidin-2(1H)-one.

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General Procedure for the Preparation of 1,4-Dihydro-pyrimidines 2a-e To a stirred mixture of 1a (1 g, 3.62 mmol) and a catalytic amount of vanadium sulfate (0.0072 g, 10 mol%) in EtOH (2.5 mL) and H2O (2.5 mL) was added dropwise 30% H2O2 (1.52 g, 13.38 mmol) over 1 h maintaining the reaction temperature at about 50 ˚C. After 8-12 h, the mixture was cooled and volatiles were evaporated under vacuum. The mixture was diluted with CH2Cl2 (10 mL) and washed with H2O (30 mL). The separated organic layer was dried with MgSO4, filtered, and concentrated to afford crude 2a. Column chromatography with EtOAc-n-hexane gave 2a as a white solid (397 mg, 48%).
Spectroscopic Data
Compound 2a: ¹H NMR (400 MHz, DMSO-d 6 ): δ = 9.30 (s, 1 H), 7.30-7.16 (m, 5 H), 5.40 (s, 1 H), 3.97 (q, J = 4.0 Hz, 2 H), 2.22 (s, 3 H), 1.12 (t, J = 2.7 Hz, 3 H). ¹³C NMR (100 MHz, CDCl3): δ = 167.4, 145.6, 143.3, 128.9, 127.7, 127.6, 100.7, 60.2, 58.0, 19.3, 14.6. ESI-MS: m/z = 245.3 [M + 1].
Compound 2b: ¹H NMR (400 MHz, CDCl3): δ = 8.27 (br s, 1 H), 7.26-6.92 (m, 4 H), 5.48 (s, 1 H), 4.08 (q, J = 4.0 Hz, 2 H), 2.62 (q, J = 4.0 Hz, 2 H), 2.22 (s, 3 H), 1.26-1.15 (m, 6 H). ¹³C NMR (100 MHz, CDCl3): δ = 167.3, 145.6, 144.4, 143.9, 142.8, 128.4, 127.5, 101.0, 60.2, 57.2, 28.9, 18.8, 15.8, 14.6. ESI-MS: m/z = 273.4 [M + 1].
Compound 2c: ¹H NMR (400 MHz, CDCl3): δ = 10.13 (s,
1 H), 9.91 (s, 1 H), 4.83 (t, J = 4.0 Hz, 1 H), 4.26 (m, 2 H), 2.48 (s, 3 H), 1.79-1.14 (m, 11 H), 0.87 (t, J = 2.7 Hz, 3 H). ¹³C NMR (100 MHz, CDCl3): δ = 164.3, 161.1, 142.7, 107.4, 61.7, 52.5, 51.7, 47.0, 36.9, 31.6, 23.3, 22.7, 17.9, 14.6, 14.3. ESI-MS: m/z = 239.3 [M + 1].
Compound 2d: ¹H NMR (400 MHz, CDCl3): δ = 7.43 (s,
1 H), 7.28-7.14 (m, 5 H), 4.63 (t, J = 4.0 Hz, 1 H), 4.18 (m, 2 H), 2.80-2.67 (m, 2 H), 2.28 (s, 3 H), 1.91-1.82 (m, 2 H), 1.26 (t, J = 3.3 Hz, 3 H). ¹³C NMR (100 MHz, CDCl3): δ = 175.9, 165.8, 165.7, 144.5, 141.1, 128.9, 128.7, 126.5, 103.2, 103.1, 60.8, 60.4, 52.3, 38.3, 30.9, 18.6, 14.7. ESI-MS: m/z = 271.4 [M + 1].
Compound 2e: ¹H NMR (400 MHz, CDCl3): δ = 7.34-6.99 (m, 4 H), 5.57 (s, 1 H), 5.40 (d, J = 4.0 Hz, 1 H), 4.09 (m,
2 H), 2.31 (s, 3 H), 1.20 (t, J = 2.7 Hz, 3 H). ¹³C NMR (100 MHz, CDCl3): δ = 167.1, 162.5 (d, J = 250.0 Hz), 145.1, 142.6, 141.4, 129.2 (d, J = 10.0 Hz), 115.6 (d, J = 20.0 Hz), 115.5, 101.2, 60.3, 57.4, 19.5, 14.6. ESI-MS: m/z = 263.3 [M + 1].

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General Procedure for the Preparation of 2-Unsubsti-tuted Pyrimidines 3a-e To a stirred solution of 2a (100 mg, 0.41 mmol) in acetone (2 mL) was added KMnO4 (87 mg, 0.55 mmol). After the complete consumption of 2a, excess of KMnO4 was decomposed by the addition of 2-PrOH. The reaction mixture was filtered through Celite and washed thoroughly with acetone (10 mL). Removal of solvent afforded product 3a (72mg, 73%) as a white solid.
Spectroscopic Data
Compound 3a: ¹H NMR (400 MHz, CDCl3): δ = 9.16 (s, 1 H), 7.68-7.43 (m, 5 H), 4.24 (q, J = 4.0 Hz, 2 H), 2.57 (s, 3 H), 1.10 (t, J = 2.7 Hz, 3 H). ¹³C NMR (100 MHz, CDCl3): δ = 167.4, 164.7, 162.9, 157.8, 137.2, 131.8, 131.5, 129.9, 128.3, 128.0, 125.7, 61.7, 22.3, 13.4. ESI-MS: m/z = 243.4 [M + 1].
Compound 3b: ¹H NMR(400 MHz, CDCl3): δ = 9.13 (s, 1 H), 7.60 (d, J = 4.0 Hz, 2 H), 7.37 (d, J = 4.0 Hz, 2 H), 4.26 (q, J = 4.0 Hz, 2 H), 2.73 (q, J = 4.0 Hz, 2 H), 2.62 (s, 3 H), 1.28 (t, J = 2.7 Hz, 3 H), 1.13 (t, J = 2.7 Hz, 3H). ¹³C NMR (100 MHz, CDCl3): δ = 168.3, 165.2, 163.6, 158.4, 147.2, 135.8, 128.8, 128.6, 126.2, 62.3, 29.1, 22.9, 15.8, 14.1. ESI-MS: m/z = 271.3 [M + 1].
Compound 3c: ¹H NMR (400 MHz, CDCl3): δ = 9.01 (s, 1 H), 4.48 (q, J = 4.0 Hz, 2 H), 2.79 (t, J = 4.0 Hz, 2 H), 2.54 (s, 3 H), 1.77-1.22 (m, 9 H), 0.92 (t, J = 2.7 Hz, 3 H). ¹³C NMR (100 MHz, CDCl3): δ = 167.8, 167.7, 164.2, 158.3, 62.2, 36.1, 31.9, 28.9, 22.9, 22.7, 14.4, 14.2. ESI-MS: m/z = 237.3 [M + 1].
Compound 3d: ¹H NMR (400 MHz, CDCl3): δ = 9.02 (s, 1 H), 7.40-7.00 (m, 5 H), 4.44 (q, J = 4.0 Hz, 2 H), 3.11-3.02 (m, 4 H), 2.54 (s, 3 H), 1.40 (t, J = 3.3 Hz, 3 H). ¹³C NMR (100 MHz, CDCl3): δ = 167.6, 166.8, 164.6, 158.5, 128.9, 128.8, 127.2, 126.7, 62.4, 38.2, 35.3, 23.2, 14.6. ESI-MS:
m/z = 271.4 [M + 1].
Compound 3e: ¹H NMR (400 MHz, CDCl3): δ = 9.14 (s, 1 H), 7.70-7.65 (m, 2 H), 7.21-7.11 (m, 2 H), 4.27 (q, J = 4.0 Hz, 2 H), 2.63 (s, 3 H), 1.18 (t, J = 2.7 Hz, 3 H). ¹³C NMR (100 MHz, CDCl3): δ = 168.1, 164.4 (d, d, J = 230.0 Hz), 164.0, 162.4, 158.5, 134.0, 131.0 (d, J = 10.0 Hz), 126.2, 116.2 (d, J = 20.0 Hz), 62.5, 23.0, 14.1. ESI-MS: m/z = 261.3 [M + 1].

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General Procedure for the Preparation of 2-Hydroxy-pyrimidines 5a-e To a stirred solution of 4a (1.0 g, 3.84 mmol) in acetone (20 mL) was added KMnO4 (1.52 g, 9.60 mmol). After the complete consumption of 4a, the excess KMnO4 was decomposed by the addition of 2-PrOH. The reaction mixture was filtered through Celite and washed thoroughly with acetone (30 mL). Removal of solvent afforded product 5a (670mg, 81%) as a white solid.
Spectroscopic Data
Compound 5a: ¹H NMR (400 MHz, CDCl3): δ = 7.61-7.41 (m, 5 H), 4.05 (q, J = 4.0 Hz, 2 H), 2.62 (s, 3 H), 0.94 (t, J = 2.7 Hz, 3 H). ¹³C NMR (100 MHz, CDCl3): δ = 167.4, 164.7, 162.9, 157.8, 137.2, 131.8, 131.7, 131.5, 129.9, 128.3, 128.0, 125.7, 61.7, 22.3, 13.4. ESI-MS: m/z = 259.3 [M + 1].
Compound 5b: ¹H NMR (400 MHz, CDCl3): δ = 7.52-7.13 (m, 4 H), 4.80-4.26 (m, 2 H), 3.01 (q, J = 4.0 Hz, 2 H), 2.84 (s, 1 H), 2.69-2.45 (m, 2 H), 2.30 (s, 3 H), 1.26 (t, J = 2.7 Hz, 3 H). ¹³C NMR (100 MHz, CDCl3): δ = 165.8, 141.0, 140.4, 129.0, 128.8, 128.7, 126.9, 126.8, 62.2, 38.8, 31.8, 31.0, 30.7, 30.1, 25.5, 14.6. ESI-MS: m/z = 287.3 [M + 1].
Compound 5c: ¹H NMR (400 MHz, CDCl3): δ = 4.42 (q, J = 2.0 Hz, 2 H), 2.80 (t, J = 2.0 Hz, 2 H), 2.53 (s, 3 H), 1.73-1.26 (m, 9 H), 0.90 (t, J = 2.7 Hz, 3 H). ¹³C NMR (100 MHz, CDCl3): δ = 166.0, 158.7, 111.8, 62.1, 32.0, 31.8, 31.5, 22.8, 14.6, 14.29, 14.26. ESI-MS: m/z = 253.3 [M + 1].
Compound 5d: ¹H NMR (400 MHz, CDCl3): δ = 7.52-7.13 (m, 5 H), 4.80-4.26 (m, 2 H), 3.01 (q, J = 4.0 Hz, 2 H), 2.84 (s, 1 H), 2.69-2.45 (m, 2 H), 2.30 (s, 3 H), 1.26 (t, J = 2.7 Hz, 3 H). ¹³C NMR (100 MHz, CDCl3): δ = 175.9, 165.8, 165.7, 144.5, 141.1, 128.9, 128.7, 126.5, 103.2, 103.1, 60.8, 52.3, 38.3, 30.9, 18.6, 14.7. ESI-MS: m/z = 287.3 [M + 1].
Compound 5e: ¹H NMR (400 MHz, CDCl3): δ = 7.65-6.97 (m, 4 H), 4.11 (q, J = 4.0 Hz, 2 H), 2.62 (s, 3 H), 1.02 (t, J = 2.7 Hz, 3 H). ¹³C NMR (100 MHz, CDCl3): δ = 165.5, 162.4 (d, J = 250.0 Hz), 146.4, 139.7, 139.6, 128.4 (d, J = 10.0 Hz), 115.5 (d, J = 20.0 Hz), 101.4, 60.1, 55.0, 18.5, 14.2. ESI-MS: m/z = 277.3 [M + 1].