Biginelli reaction on 4-oxo-4H-1-benzopyran-3-carboxaldehyde- a search for reaction pathway

Abstract

On heating a mixture of 3-formylchromone 1, active methylene compound 2 or 3 and urea (4) in AcOH produces dihydropyrimidinones 10 or 11, whereas use of thiourea in place of urea produces 1,3-thiazine derivative 14 or 15 and the above reactions pass through the Knoevenagel condensate 5 or 6.