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Metal-Catalyzed Oxidations with Pinane Hydroperoxide:  A Mechanistic Probe To Distinguish between Oxometal and Peroxometal Pathways

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journal contribution
posted on 18.02.1998, 00:00 by H. E. B. Lempers, A. Ripollès i Garcia, R. A. Sheldon
The relative reactivities of tert-butyl hydroperoxide (TBHP) and pinane hydroperoxide (PHP) in metal (Cr, Mo, Ru, Se, V, and Zr)-catalyzed oxidations were compared. When these oxidations involve rate-limiting oxygen transfer from a peroxometal species to the substrate huge differences between TBHP and PHP were observed, e.g., molybdenum-catalyzed epoxidation of cyclohexene with TBHP gave a 98% yield while PHP gave 0%. When the reaction involves reaction of an oxometal species with the substrate as the rate-limiting step, little or no difference is observed, e.g., the selenium-catalyzed allylic oxidation of β-pinene gave a 96% and 99% yield with TBHP and PHP, respectively. Small but significant differences are observed when reoxidation of the catalyst by the hydroperoxide to the active oxometal species is the rate-limiting step; e.g., the chromium-catalyzed oxidation of carveol gave carvone in 89% and 24% yield with TBHP and PHP, respectively. Hence, the effect of RO2H structure on rate is dependent on the rate-limiting step.