The first syntheses of sterol biosynthetic intermediates zymosterol (4), 4, 4-dimethylzymosterol (5), cholesta- 8, 14, 24-trien-3β-ol (6), the 4, 4-dimethyl analogue 7, and fecosterol (8) are described in detail. Multigram quantities of key intermediates 16 and 17 were efficiently prepared from known enones 20 and 21 (eight steps, 35% overall yield). Novel entry into Δ8-sterols was achieved through regiospecific hydroboration/deoxygenation of the 8, 14-diene systems. Sterols containing Δ24- or Δ24(28)-olefins were obtained from C24-hydroxy intermediates either via dehydration using bis[α, α-bis(trifluoromethyl)benzenemethanolato]diphenylsulfur in CH2Cl2 or via Swern oxidation/Wittig olefination, respectively. In this way, 16 and 17 were converted to the desired Δ8, 24-, Δ8, 14, 24-, and Δ8, 24(28)-sterols with high regiocontrol.