A diastereomer of wortmannilactone C has been synthesized according to a convergent and versatile strategy from tert-butyl 3-hydroxypropanoate and ethyl (R)-3-hydroxybutanoate. The key steps are a Liebeskind cross-coupling and a Horner-Wadsworth-Emmons (HWE) reaction to construct the macrolactone. The stereogenic centers at C9, C11, and C21 were controlled by enantioselective allyltitanations, and the C19 stereocenter was controlled by using a Noyori reduction of an acetylenic ketone.