A Novel Copper-Catalyzed Preparation of Pyrido[1,2-a]pyrimidine Derivatives

Abstract

A copper-catalyzed reaction of 2-amino-1-(prop-2-yn-1-yl)pyridinium bromide derivatives and aromatic sulfonyl azides has been demonstrated under mild condition.

Key words

copper-catalyzed - ketenimine - pyrido[1,2-a]pyrimidine - sulfonyl azide - 2-amino pyridine

• References and Notes

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• 21 General Procedure for the Preparation of Pyrido[1,2-a]pyrimidines 9a–i: To the stirred solution of alkyne (1 mmol), azide (1 mmol), CuI (10 mol%) in DMF (3 mL), Et₃N (1 mmol) was added under N₂. The mixture was stirred at r.t. for 12 h. After dilution with CH₂Cl₂, the aqueous solution of NH₄Cl was added and the stirring was continued for 30 min. The aqueous layer was extracted with CH₂Cl₂ and dried over Na₂SO₄. The solvent was removed under reduced pressure and the residue was purified by column chromatography (EtOAc–EtOH, 10:1) to afford the pure product. N-(2H-Pyrido[1,2-a]pyrimidin-2-ylidene)benzenesulfonamide (9a): yield: 0.23 g (79%); pale yellow powder; mp 254–256 °C. IR (KBr): 3283, 1644, 1463, 1321, 1130, 763, 692 cm^–1. ¹H NMR (500 MHz, DMSO-d ₆): δ = 6.94 (d, J = 7.5 Hz, 1 H), 7.25 (dt, J = 6.8, 1.0 Hz, 1 H), 7.40 (d, J = 9.0 Hz, 1 H), 7.45–7.49 (m, 3 H), 7.92–7.95 (m, 3 H), 8.41 (d, J = 6.6 Hz, 1 H), 8.53 (d, J = 7.5 Hz, 1 H). ¹³C NMR (125 MHz, DMSO-d ₆): δ = 114.8, 123.9, 124.3, 127.6, 129.1, 133.7, 135.6, 139.3, 143.8, 148.1, 149.5, 160.9. Anal. Calcd for C₁₄H₁₁N₃O₂S: C, 58.94; H, 3.89; N, 14.73. Found: C, 58.73; H, 3.75; N, 14.99.