Diastereocontrolled synthesis of unit A of cryptophycin

Cryptophycin fragment A was prepared in 11 steps from protected methyl (R)-mandelate 4. A diastereoselective addition of magnesium acetylide to methyl mandelate and a Sharpless epoxidation followed by regioselective opening of the resulting epoxide allowed the synthesis of this intermediate in high diastereomeric purity.