Synthesis of milbemycins from avermectins

Abstract The structure of the avermectins and the milbemycins were interrelated by the conversion of 22,23-dihydroavermectin B 1a and B 1b aglycones ( 4 ) into 13-deoxy-22,23-dihydroavermectin B 1a aglycone ( 9 ) and 13-deoxy-22,23-dihydroavermectin B 1b aglycone ( 11 ) corresponding to 26-ethyl milbemycin-α 3 and milbemycin B-41D respectively via reduction of the protected 13-chloroaglycone derivatives.