Synthesis and Configuration of Some Hydroxymilbemycin Derivatives Including 22,23-Dihydroavermectin B1b Aglycone

The synthesis of several configurationally defined hydroxymilbemycin derivatives is described. One of these allylic alcohols is the known 5‐O‐[(tert‐butyl)dimethylsilyl]‐13α‐hydroxymilbemycin D (= 5‐O‐[(tert‐butyl)‐dimethylsilyl]‐22,23‐dihydroavermectin B1b, aglycone; 15D), the synthesis of which represents LI conversion of the milbemycin to the avermectin series of natural products. The configurations at C(13), C(14), and C(15) of the new milbemycin derivatives were determined by NMR experiments and force‐field calculations.