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Please login to access the full content or check if you have access via Variation 2: Allylic Oxidation with Peroxides and Catalytic Metal Salts

DOI: 10.1055/sos-SD-026-00987

Marsden, S. P.Science of Synthesis, (2005261046.

One significant drawback of the use of chromium-based oxidants is that they are usually required to be present in vast excess (typically 1020-fold) for efficient reaction, with associated problems in separation and disposal of the toxic chromium waste. The use of tert-butyl hydroperoxide as co-oxidant allows a reduction in the amount of chromium to 2 molar equivalents of pyridinium dichromate, as in the conversion of 1-phenylcyclohexene (6) into cyclohexenone 7 (Scheme 2).[‌7‌] Unfortunately the yields for this protocol are not as uniformly high as for some of the processes described in Section A more recent report suggests that chromium-pillared clay can be used with the same co-oxidant to effect allylic oxidations.[‌8‌] Other metal salts mediate efficient allylic oxidation of alkenes with tert-butyl hydroperoxide (as in the oxidation of cholesteryl ester 8 to 9), including systems based upon rhodium,[‌9‌] ruthenium,[‌10‌] and copper.[‌11‌] A more recent report identifies a range of heterogeneous catalysts based upon immobilized carboxylate salts of cobalt(II), copper(II), manganese(II), and vanadium(II) as recyclable catalysts for allylic oxidations.[‌12‌]

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