Chalcones, flavanones, and flavonols, including 8-methoxybutin isolated from Coreopsis lanceolata L. petals, were successfully synthesized with total yields of 2–59% from O-methylpyrogallols using the Horner–Wadsworth–Emmons reaction as a key reaction. Aurones, including leptosidin, were also successfully synthesized with 5–36% total yields using the Aldol condensation reaction as a key reaction. Each chalcone, flavanone, flavonol, and aurone with the 3,4-dihydroxy groups in the B-ring showed high antioxidant activity. Additionally, each of the chalcones, flavanones, flavonols, and aurones with the 2,4-dihydroxy groups in the B-ring showed an excellent whitening ability.