Stereocontrolled Synthesis of a C n –C n +6 Building Block for the Unnatural Enantiomers of Important Polyol,Polyene Antibiotics from an Epoxy Alcohol by a Reduction/Conjugate Addition/Hydroxylation Sequence

Epoxy alcohol anti ‐ 10 , derived from a desymmetrizing Sharpless epoxidation (up to 97 % ee ) of divinylcarbinol 9 , provided the unsaturated 1,3‐diol syn ‐ 11 upon treatment with RedAl ® ; syn ‐ 11 was converted into the α,β‐unsaturated esters ( E )‐ or ( Z )‐ 7b in three steps. Cu‐promoted 1,4‐addition of vinylmagnesium halides to the ( E )‐ester proceeded with diastereoselectivities of up to 91 % and Cu‐catalyzed 1,4‐additions with diastereoselectivities of up to 82 %. The potassium enolate of the major vinylation product syn ‐ 22b was hydroxylated by the Davis oxaziridine with perfect but unprecedented diastereoselectivity. The resulting hydroxy ester, α,β syn , β,γ syn ‐ 32 , furnished the “eastern moiety” building block 6 of the title compounds in three steps.