Selective oxidation of lupeol by iodosylbenzene catalyzed by manganese porphyrins.

Abstract

Manganese porphyrin-catalyzed oxidation of lupeol by iodosylbenzenewas achieved undermild conditionswith low isolated yields but with remarkable selectivity, depending on the catalyst of choice. Mn(III) mesotetraphenylporphyrin and Mn(III) meso-tetrakis(4-carbomethoxyphenyl)porphyrin provided an entry for the preparation of 3β,30-dihydroxylup-20(29)-ene (6–14% yields), whereas Mn(III) β-octabromo-meso-tetrakis(4- carbomethoxyphenyl)porphyrin led to 20-oxo-3β-hydroxy-29-norlupeol (6% yield), as single products. Unreacted lupeol was recovered in quantitative yield. The oxidative transformations at lupeol C20 or C30 take place with no need for protection of C3 hydroxyl moiety.