The Guareschi–Thorpe Cyclization Revisited – An Efficient Synthesis of Substituted 2,6-Dihydroxypyridines and 2,6-Dichloropyridines

Abstract

DBU as base is key in a practical modified Guareschi–Thorpe cyclization of β-keto esters and 2-cyanoacetamide to allow the synthesis of substituted pyridones in good to excellent yields. The chlorination of DBU salts of pyridones with POCl3 in the presence of a quaternary ammonium salt under standard atmospheric reflux conditions as opposed to the typical pressure equipment led to high yields of substituted 2,6-dichloropyridines.