A highly efficient regioselective one-pot synthesis of 2,3,6-trisubstituted pyridines and 2,7,7-trisubstituted tetrahydroquinolin-5-ones using K5CoW12O40·3H2O as a heterogeneous recyclable catalyst

A systematic investigation into the regioselective one-pot, three-component condensation of enaminones 1a–g, β-dicarbonyl compounds 2a–c, and ammonium acetate in the presence of a catalytic amount of K₅CoW₁₂O₄₀·3H₂O (0.01 equiv or 1.0 mol %) under solvent free conditions, as well as in refluxing isopropanol, has been reported. The reaction was highly efficient to produce 2,3,6-trisubstituted pyridines 3a–g, 4a–g, and novel 2,7,7-trisubstituted-5,6,7,8-tetrahydroquinoline-5-ones 5a–g in excellent yields. The present procedure offers advantages of short reaction time, simple work-up, and the catalyst exhibited remarkable reusable activity.