Synthetic study of 1,7,9-trideoxypaclitaxel via sinenxan A

Sinenxan A, a biosynthetic taxane, was converted into compound 9, a key intermediate of 1,7,9-trideoxypaclitaxel. Two special steps in this transformation are worthy of note: (1) regioselective removal of C-5-acetyl; and (2) stereoselective reduction of the 13-carbonyl group by transannular assistance from the C-4-hydroxyl.