Synlett 2014; 25(13): 1916-1920
DOI: 10.1055/s-0034-1378320
letter
© Georg Thieme Verlag Stuttgart · New York

Synthesis of Imidazoles and Pyrimidines Using Palladium-Catalyzed Decar­boxylative Intramolecular Condensation of 1,2,4-Oxadiazol-5(4H)-ones

Takuya Shimbayashi
Department of Energy and Hydrocarbon Chemistry, Graduate School of Engineering, Kyoto University, Katsura, Nishikyo-ku, Kyoto 615-8510, Japan   Fax: +81(75)3832499   Email: kokamoto@scl.kyoto-u.ac.jp   Email: ohe@scl.kyoto-u.ac.jp
,
Kazuhiro Okamoto*
Department of Energy and Hydrocarbon Chemistry, Graduate School of Engineering, Kyoto University, Katsura, Nishikyo-ku, Kyoto 615-8510, Japan   Fax: +81(75)3832499   Email: kokamoto@scl.kyoto-u.ac.jp   Email: ohe@scl.kyoto-u.ac.jp
,
Kouichi Ohe*
Department of Energy and Hydrocarbon Chemistry, Graduate School of Engineering, Kyoto University, Katsura, Nishikyo-ku, Kyoto 615-8510, Japan   Fax: +81(75)3832499   Email: kokamoto@scl.kyoto-u.ac.jp   Email: ohe@scl.kyoto-u.ac.jp
› Author Affiliations
Further Information

Publication History

Received: 07 May 2014

Accepted after revision: 13 May 2014

Publication Date:
25 June 2014 (online)


Abstract

We found that 1,2,4-oxadiazol-5(4H)-ones acted as iminonitrene equivalents in the presence of a palladium catalyst and a stoichiometric amount of phosphine and that aza-Wittig-type condensation with the internal carbonyl moiety occurred to afford the corresponding imidazoles and pyrimidines.

Supporting Information

 
  • References and Notes


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  • 8 General Procedure for the Catalytic ReactionsA solution of Pd(PPh3)4 (6.9 mg, 6.0 μmol) and oxadiazolone 3 (0.20 mmol) in 1,4-dioxane (1.5 mL) was stirred at 80 °C for 24 h. The reaction mixture was filtered through a pad of Florisil®, and the filtrate was concentrated under vacuum. The residue was subjected to column chromatography on Florisil® (hexane–EtOAc = 4:1) to afford imidazole 4.Imidazole 4aWhite solid (43.8 mg, 0.20 mmol, 99% yield; mp 160.1–160.5 °C). 1H NMR (400 MHz, CDCl3): δ = 7.22–7.45 (m, 7 H), 7.75 (d, J = 7.4 Hz, 2 H), 7.87 (d, J = 7.3 Hz, 2 H). 13C NMR (100 MHz, acetone-d 6): δ = 114.3, 125.4, 125.9, 127.2, 129.0, 129.3, 129.5, 131.8, 135.6, 142.6, 147.4. HRMS–FAB: m/z calcd for C15H13N2 [M + H]+: 221.1079; found: 221.1069.Imidazole 4cWhite solid (46.0 mg, 0.19 mmol, 97% yield; mp 65.0–66.1 °C). 1H NMR (400 MHz, CDCl3): δ = 7.08 (dd, J HH = 8.8 Hz, J HF = 8.8 Hz, 2 H), 7.27 (t, J = 7.3 Hz, 1 H), 7.37 (s, 1 H), 7.39 (t, J = 7.3 Hz, 2 H), 7.74 (d, J = 7.3 Hz, 2 H), 7.82 (dd, J HH = 8.3 Hz, J HF = 4.9 Hz, 2 H). 13C NMR (100 MHz, CDCl3): δ = 115.7 (d, J CF = 21.7 Hz), 117.7, 125.0, 126.4 (d, J CF = 3.1 Hz), 127.2, 127.3, 127.5 (d, J CF = 8.0 Hz), 128.8, 132.4, 146.7, 163.0 (d, J CF = 248 Hz). HRMS–FAB: m/z calcd for C15H12FN2 [M + H]+: 239.0985; found: 239.0990.Imidazole 4iWhite solid (30.1 mg, 0.13 mmol, 67% yield; mp 168.5–171.0 °C). 1H NMR (400 MHz, CDCl3): δ = 7.08 (dd, J = 5.1, 3.9 Hz, 1 H), 7.27 (t, J = 7.3 Hz, 1 H), 7.34 (d, J = 5.1 Hz, 1 H), 7.35 (s, 1 H), 7.39 (d, J = 8.1 Hz, 2 H), 7.41 (d, J = 3.7 Hz, 1 H), 7.72 (br s, 2 H). 13C NMR (100 MHz, acetone-d6 ): δ = 116.4, 124.1, 125.2, 126.3, 127.0, 128.2, 129.0, 134.4, 135.2, 140.5, 143.1. HRMS–FAB: m/z calcd for C13H11N2S [M + H]+: 227.0643; found: 227.0639.Imidazole 4jPale yellow solid (35.0 mg, 0.14 mmol, 70% yield; mp 124.3–126.2 °C). 1H NMR (400 MHz, CDCl3): δ = 3.84 (s, 3 H), 6.93 (d, J = 8.8 Hz, 2 H), 7.27 (d, J = 8.5 Hz, 2 H), 7.35 (t, J = 7.6 Hz, 1 H), 7.42 (t, J = 7.8 Hz, 2 H), 7.67 (d, J = 8.5 Hz, 2 H), 7.87 (d, J = 7.1 Hz, 2 H). 13C NMR (100 MHz, acetone-d6 ): δ = 55.3, 114.6, 125.7, 125.8, 126.6, 128.7, 129.3, 129.9, 131.1, 131.8, 146.9, 159.4. HRMS–FAB: m/z calcd for C16H15N2O [M + H]+: 251.1184; found: 251.1181.Imidazole 4oWhite solid (29.7 mg, 0.19 mmol, 94% yield; mp 180.5–181.6 °C). 1H NMR (400 MHz, CDCl3): δ = 2.29 (s, 3 H), 6.82 (s, 1 H), 7.31 (t, J = 6.4 Hz, 1 H), 7.37 (t, J = 6.8 Hz, 2 H), 7.81 (d, J = 7.8 Hz, 2 H). 13C NMR (100 MHz, CDCl3): δ = 12.0, 119.4, 125.0, 128.2, 128.8, 130.4, 132.1, 146.0. HRMS–FAB: m/z calcd for C10H11N2 [M + H]+: 159.0922; found: 159.0923.

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  • 15 Only 15% of imidazole 4a was obtained in the reaction of the stoichiometric amount of Pd2(dba)3 with oxadiazolone 3a (Scheme 8). This result indicates that the reaction pathway bypassing the iminophosphorane intermediate (path b) also exists but is only a minor pathway.