A synthesis of cytotoxic agent Cryptophycin 4 features a new approach to (5
S,6R)-5-hydroxy-6-methyl-8-phenyl-(2E,7E)-dienoic acid in which the anti st
ereochemistry between two stereogenic centres is secured by addition of a 1
,3-dioxan-4-ylcopper(I) reagent to a planar chiral molybdenum cationic comp
lex.