This paper presents the synthesis of γ-halo-δ-lactones, δ-iodo-γ-lactones and δ-hydroxy-γ-lactones from readily available organic substrates such as trans-crotonaldehyde and aryl bromides. Crystal structure analysis was carried out for lactones that were obtained in crystalline form. All halo-δ-lactones and δ-hydroxy-γ-lactones were highly cytotoxic against gastric cancer AGS cells with IC50 values in the range of 0.0006–0.0044 mM. Some lactones showed high bactericidal activity against E. coli ATCC 8739 and S. aureus ATCC 65389, which reduced the number of CFU/mL by 70–83% and 87% respectively.