To develop the Javanese ginger Bangle (Zingiber purpureum), which contains neurotrophic phenylbutenoid compounds named banglenes 1 and 2, as a functional food additive for protection of neurodegenerative disease, we investigated conversion method from 3 to 1 and 2 under practical conditions available in food processing steps. After several trials, we found that dimerization of 3 proceeded smoothly under refluxing EtOH/H 2 O (1/3) in the presence of ubiquinone (0.1 eq) in sealed tube, giving rise to 1 and 2 in 54% yield. When this condition was applied for 70% EtOH extract of bangle, content of 1 and 2 in the extract was increased 2-fold by 2.1%.