Regio- and stereoselective C-H functionalization of brassinosteroids.

Late stage CH functionalization is a powerful tool for modification of natural compounds. Herein we report that the rhodium-catalyzed reaction of brassinosteroids with aryloxysulfonamides proceeds regio- and stereoselectively at C15 position. The derivative obtained from 24-epibrassinolide was easily transformed to the conjugate with a BODIPY dye bearing unaffected functional groups of the native brassinosteroid.

Stereoselective synthesis of α-methyl and α-alkyl ketones from esters and alkenes via cyclopropanol intermediates.

Alkenes bearing a stereocenter in the allylic position were found to undergo Kulinkovich hydroxycyclopropanation with good diastereoselectivity. For the isomerization of the resulting cyclopropanols to diastereomerically enriched α-methyl ketones, a new mild regioselective method has been developed. A sequence of stereoselective cyclopropanation and cyclopropanol ring opening was successfully employed for the construction of the C20 stereocenter in steroids.