Cyclopropylacetaldehyde is used as a reagent in the synthesis of 7-benzyl-4-hydroxy-1,5-naphthyridin-2(1H)-one which has anti-HIV activity. Also used as a reagent in the synthesis of 5,6-dihydro-1H-pyridin-2-ones as potent inhibitors of HCV NS5B polymerase.