Wittig reaction
Molecular simplification began first by disconnecting both carbon chains with a Wittig reaction and Horner-Wadsworth Emmons modification. The Wittig reaction affords the "cis" product, while the Horner-Wadsworth Emmons produces the "trans" olefin. The published synthesis reveals a 1:1 diastereomeric mixture of the carbonyl reduction using zinc borohydride. However, years later Corey and co-workers established the CBS reduction. One of the examples that exemplified this protocol was an intermediate in the prostaglandin synthesis revealing a 9:1 mixture of the desired diastereomer (scheme 24).