The oxidation of 2'-O-acetyl-4''-O-formyl-8,9-didehydroerythromycin A 6,9-hemiacetal (I) gives the corresponding 11-oxo derivative (II), which was first methylated with NaH and methyl iodide and then hydrolyzed with NaHCO3 to yield 11-deoxy-12-O-methyl-1-oxo-8,9-didehydroerythromycin A 6,9-hemiacetal (III). The demethylation of (III) with I2 and NaOH affords the 3'-N-demethyl derivative (IV), which is finally alkylated with isopropyl iodide and diisopropylethylamine in methanol.