<p>The oxidative aromatization of 1,3,5-trisubstituted 2-pyrazolines was effectively accomplished using the <i>trans</i>-5-hydroperoxy-3,5-dimethyl-1,2-dioxolan-3-yl ethaneperoxate (THDDE)/KOH system. Singlet oxygen (¹O₂) served as the main active oxidant utilized in this procedure, and it was generated by the breakdown of THDDE aided by KOH. This protocol offers an easy and specific approach for the oxidative aromatization of 1,3,5-trisubstituted 2-pyrazolines. The oxidation of 2-pyrazolines with singlet oxygen was chemoselective, and different 1,3,5-trisubstituted 2-pyrazolines were converted into the corresponding 1,3,5-trisubstituted pyrazoles in quantitative yields within short reaction times.</p> Graphical abstract <p></p>