The C1-C9 fragment of callipeltoside (17) was prepared in 12 steps and 7.2%
overall yield from bicyclic lactone (+)-4. Key steps include a stereoselec
tive epoxidation and further regiocontrolled nucleophilic opening of the ox
irane ring to install two vicinal stereocenters (C5 and C6), and the use of
bis(trimethylsilyl) peroxide and a catalytic amount of Sn(IV) chloride for
the chemoselective Baeyer-Villiger oxidation of unsaturated cyclopentanone
15.