Isoxazoles and pyrazoles as the five member heterocyclic compounds often play important roles in biologically active natural products and synthetic compounds of medicines [1]. Isoxazoles and 2-pyrazoles have been obtained respectively by oxidative aromatization of isoxazolines and 2-pyrazolines [2]. Variety of reagents have been used previously for this oxidation. However, most of these methods suffer from the use of strong oxidants and require intensive reaction conditions or the need for excess oxidant or long times and afford only poor to moderate yields of products [2]. Recently, gem-dihydro peroxides have been synthesized and have been used for oxidation reactions [3]. We have synthesized trans-3,5-dihydroperoxy-3,5-dimethyl-1,2-dioxalane and used it as a powerful oxidant in organic reactions [4]. For more stabilization, we have mixed it with urea (2 mmol urea and 1 mmol peroxide) and due to hydrogen bonding, urea-trans-3,5-dihydro peroxy-3,5-dimethyl-1,2-dioxalane (UDHPDMDO) is stabilized (Scheme 1). Then, this mixture has been used for oxidative aromatization of isoxazolines and 2-pyrazolines to corresponding isoxazoles and 2-pyrazoles in excellent yields and high purity in H2O/MeCN as a solvent at room temperature.
