Application of 1-Vinylimidazole in Diels-Alder Reaction of 5,5′-bi-1,2,4-Triazines [1]

Abstract

5,5′-bi-1,2,4-Triazines undergo inverse electron demand Diels-Alder reaction with 1-vinylimidazole to give single [4+2] cycloaddition products. The reaction of the latter with cyclic enamines leads to unsymmetrical, 2,2′-bipyridines with attached cycloalkene ring.

5,5′-bi-1,2,4-triazines - 1-vinylimidazole - [4+2] cycloaddition - unsymmetrical 2,2′-bipyridines

References

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<A NAME="RG23402ST-16">16</A>

Synthesis of 7. To a solution of 3,3′-bis(methylsulfanyl)-5,5′-bi-1,2,4-triazine 1 1 g (4 mmole) in 10 mL bromobenzene 1-vinylimidazole 6 1.51 g (16 mmole) was added. The mixture was refluxed for 20 h. The solvent was evaporated under reduced pressure. The residue was purified by column chromatography using chloroform as eluent to give 0.62 g (63%) 7 as yellow solid. Mp 147-148 °C. ¹H NMR (CDCl₃): δ = 2.68 (s, 3 H), 2.74 (s, 3 H), 7.37 (dd, 1 H, J = 0.9, 8.0 Hz), 7.67 (t, 1 H, J = 7.6 Hz), 8.19 (dd, J = 0.9, 7.6 Hz, 1 H), 9.96 (s, 1 H). Anal. Calcd for C₁₀H₁₀N₄S₂: C, 48.00; H, 4.00; N, 22.40. Found: C, 48.09; H, 4.07; N, 22.02.

<A NAME="RG23402ST-17">17</A>

Synthesis of 8: A solution of the 3-(methylsulfanyl)-5-[6-(methylsulfanyl)pyridin-2-yl]-1,2,4-triazine 7 0.25 g (1 mmol) and the appropriate enamine 2a-d (2 mmol) was heated at reflux for 2 h. The solution was removed under reduced pressure. The crude product was purified by column chromatography on silica gel (Merck type 60, 230-400 mesh) using the mixture hexane/chloroform (10:1) as eluent. 8a: Mp 136-137 °C. ¹H NMR (CDCl₃): δ = 2.16 (quintet, J = 7.7, Hz, 2 H), 2.67 (s, 3 H), 2.70 (s, 3 H), 2.84 (t, J = 7.5 Hz, 2 H), 2.99 (t, 2 H, J = 7.7 Hz), 7.17 (dd, J = 0.7, 7.9 Hz, 1 H), 7.60 (t, J = 7.8 Hz, 1 H), 8.09 (s, 1 H), 8.17 (dd, J = 0.7, 7.7 Hz, 1 H). Anal. Calcd for C₁₅H₁₆N₂S₂: C, 62.50; H, 5.55; N, 9.72. Found: C, 62.39; H, 5.72; N, 9.64.

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