PROCESS FOR PREPARING MILBEMYCIN DERIVATIVES AND CERTAIN NOVEL COMPOUNDS EMPLOYED THEREIN

PURPOSE:To obtain the titled compound useful as a synthetic intermediate of miticide, insecticide and anthelmintic agent, in high yield, by reacting a 5-ketomilbemycin derivative with selenium dioxide in the presence of a carboxylic acid. CONSTITUTION:A mixture of the compounds of formula II and III can be prepared by reacting the compound of formula I (R is methyl, ethyl, isopropyl or sec-butyl) with selenium dioxide in the presence of a carboxylic acid of formula R -COOH (R is H or lower alkyl) at 0-80 deg.C. The amounts of the compounds of formula II and III depend upon the kind of the carboxylic acid and the amount of selenium dioxide, etc. If necessary, the product can be converted completely to the compound of formula II by hydrolysis. When the compound of formula III is required, it can be prepared by separating and purifying from the reaction mixture. The compound of formula III is novel. The amount of the carboxylic acid is >=1mol, and that of selenium dioxide is 1-10mol, preferably 1-3mol per 1mol of the compound of formula I.