Four 2-cyano-cinnamates and six 4H-chromene derivatives were synthesized from aromatic aldehydes with cyanoacetates via solvent-free Knoevenagel condensation using K2CO3 as catalyst under ultrasound irradiation. The experimental results indicate that the yield of methyl 2-cyano-cinnamate is up to 94.6% after reaction for 30 min at room temperature under ultrasonic power of 150 W when the dosages of benzaldehyde, methyl cyanoacetate and K2CO3 are 10, 10 and 1 mmol, respectively. However, for the 4-substituted benzaldehyde with electron-donating groups, the yields of condensation with cyanoacetate significantly decrease in the same condition. In contrast, the yield of 4H-chromene derivative is up to 91% after reaction for 20 min at 30 ℃ under ultrasonic power of 250 W when the amounts of salicylaldehyde, ethyl cyanoacetate and K2CO3 are 10, 22.5 and 0.1 mmol, respectively. However, 5-substituted salicylaldehyde with electron-donating groups can’t react with cyanoacetate. The products were characterized by mp, IR and 1H NMR．
