SeO2 based samples are tested for the oxidation of α-pinene, in liquid phase employing ethanol as the solvent. Commercial SeO2 was tested under both reflux and under 6 atm O2 pressure. At conversion levels of approximately 40%, the yield to myrtenal was much higher in the latter (34.4%) than in the former case (18.0%) due to the high oxidant species availability. Besides the high yield attained at relatively short reaction time. A palladium promoted selenium dioxide supported catalyst (Pd/SeO2/SiO2) was prepared, characterized, and submitted to the catalytic test. Selenium dioxide (14.4%) was strongly fixed to the silica support. Upon the palladium introduction (0.98%), the reducibility of SeO2 is modified, which originates a selenium species activation towards the allylic oxidation. A 12% conversion level is attained over Pd/SeO2/SiO2 following 8 h of reaction time, employing ethanol as the solvent at 134 °C. The main product is myrtenal, being obtained with a selectivity of 62%. Over oxidation products are not detected. The palladium/selenium dioxide sample is easy to handle with and its recuperation following the reaction in liquid phase is possible.
Total synthesis of clavosolide A via tandem allylic oxidation/oxa-conjugate addition reaction