Synthesis of the shark repellent pavoninin-4.

[reaction: see text] The first synthesis of the shark repellent pavoninin-4, 3, was achieved in 12 steps with 21% overall yield from diosgenin, 8. Key reactions involve an efficient synthesis of the C-15alpha hydroxyl steroid from a C-16beta hydroxyl steroid by an unexpected 1,2-transposition strategy, a stereospecific glycosylation of a hindered C-15alpha alcohol using glycosyl fluoride as a glycosyl donor and a highly chemoselective acetylation of the C-26 primary alcohol by catalytic transesterification.