Abstract: This invention provides a process for preparing a compound of the formula (I): wherein R1 is H or a hydroxyimino-protecting group; R2 is H, C1-4 alkyl or C1-4 alkoxy; R3 is C1-8 alkyl, C2-8 alkenyl or C3-8 cycloalkyl, and R4 is H, halo, C1-4 alkyl or C1-4 alkoxy, which process comprises the steps of (a) reacting an avermectin B2 derivative with an oxidizing agent to form a 5-oxo compound; (b) allowing the 5-oxo compound to react with a compound of formula R1—O—NH2 wherein R1 is H or a hydroxyimino-protecting group, to form a 5-imino compound; (c) reacting the 5-imino compound with a thionocarbonizing agent to form a 4″, 23-bisthionocarbonyl ester; (d) reacting the 4″, 23-bisthionocarbonyl ester with a deoxygenation agent to form a 4″, 23-dideoxy compound; and (e) reacting the R″, 23-dideoxy compound with an acid to form a compound of the formula (I).