Synthesis and crystal structure of 2′,4″ -O-bis(trimethylsilyl)erythromycin a 9-O-(1-isopropoxycyclohexyl) oxime

The ratio of E/Z of 2′-,4″-O-bis(trimethylsilyl)erythromycin A 9-O-(1-isopropoxycyclohexyl) oxime were much higher prepared in CH ₃CN than those in CH₂Cl₂. And the ratio would increase with elevation of temperature. Compared with 2′-OH, 4″-OH was liable to be silylated in the presence of 1,1,1,3,3,3-hexamethyldisilizane and an NH₄⁺. The crystal structure of E-title compound was determined by single-crystal X-Ray structure analysis to elucidate the origin of regioselectivity occurring at 6-hydroxyl group in the O-methylation of erythromycin A.