New oxidative tools for the functionalization of the cephalostatin north 1 hemisphere.

Dimethyldioxirane (DMDO) C-H oxidation of ketone 17 to hemiketal 18 (82%), bis-dehydration to vinyl ether 21 (77%), and DMDO again provides C-23 axial alcohol 23 (99%). Routine processing, including a double-stereoselective Sharpless AD reaction (de >98%), gives alcohols 7 and 32. C-23 deoxy substrate 7 undergoes Suarez hypoiodite oxidative cyclization to (natural) beta spiroketal 34, but compound 32, bearing a C-23 silyl ether, generates unnatural spiroketal 33. [reaction: see text]