The reaction of 16,16-dimethyl-PGE2 methyl ester bis(trimethylsilyl) ether (I) with the reaction product of N,S-dimethyl-S-phenylsulfoximine and methylmagnesium chloride (II) in THF at -78 C followed by a treatment with AlHg and acetic acid gives 9-deoxy-9-methylene-16,16-dimethyl-PGE2 methyl ester (III), which is hydrolyzed with KOH in methanol - water.