Anthelmintic milbemycins and avermectins

A process for preparing a compound of formula (I):

• ##STR98## wherein R.sup.1 is hydrogen or optionally protected hydroxy;
• R.sup.2 is alkoxy, optionally protected hydroxy, oxo, oximino, or oximino substituted by an organic radical;
• R.sup.3 is hydrogen, optionally protected hydroxy, or a group 4'-(.alpha.-L-oleandrosyl)-.alpha.-L-oleandrosyloxy or .alpha.-L-oleandrosyloxy wherein the terminal hydroxy group is optionally protected;
• R.sup.4, R.sup.5, R.sup.6, and R.sup.7 are the same or different and each is hydrogen or an organic radical;
• and
• R.sup.8 is amino, imino, amino substituted by an organic radical, imino substituted by an organic radical, optionally protected hydroxy, or oxo, which process comprises:
• (a) treating a compound of formula (III) ##STR99## with a compound selected from the group consisting of MC.tbd.C--CR.sup.4 R.sup.5 --CR.sup.6 R.sup.7 OP, MCH.sub.2 CR.sup.8 --CR.sup.4 R.sup.5 --CR.sup.6 R.sup.7 OP, and MCH.sub.2 CR.sup.20 --CR.sup.4 R.sup.5 --CR.sup.6 R.sup.7 OP, wherein M is a metalating agent, P is a protecting group, and R.sup.20 is optionally protected ketone;
• (b) treating the compound obtained from step (a) with an acid/R.sup.18 OH to obtain a compound of formula (II), (IV), or (V) as defined in claim 12;
• and
• (c) carrying out in-situ acid-catalyzed cyclization of the compound of formula (II), (IV), or (V) obtained in step (b).