N-propargylation reaction of substituted 4H-pyrano[2,3-d]pyrimidine derivatives under conventional, ultrasound- and microwave-assisted conditions

A series of substituted 4 H -pyrano[2,3- d ]pyrimidines were synthesized from corresponding substituted 4 H -pyrans by ring-closing reaction with acetic anhydride or acetic acid in the presence of trifluoroacetic acid as catalyst. The successive alkylation reaction of lactam N–H bond on pyrimidine-4-one ring was carried out using propargylic bromide in dry acetonitrile in the presence of anhydrous potassium carbonate. Three procedures applied for this purpose, including MW-assisted heating conditions at power of 100 W, under conventional heating conditions in water bath at 50 °C, and under ultrasound-assisted heating conditions at 50 °C. Dry acetonitrile was used as reaction solvent. Excellent yields of N -propargyl-4 H -pyrano[2,3- d ]pyrimidine derivatives were obtained. The single-crystal X-ray structure of compound 6a has been recorded, and the study helps to confirm the structure of synthesized N -propargyl derivative of 4 H -pyrano[2,3- d ]pyrimidines 6a – 6p .