Transformations of Seven-Membered Terpene Lactones toward Low-Molecular-Weight Bioregulators

The review describes low-temperature reduction of (–)-mentholactone with diisobutylaluminum hydride in methylene chloride. Depending on the conditions, three products are formed: (2S,4R,7S)-7-isopropyl-4-methyloxepan-2-ol [(–)-mentholactol), (6R)-8-hydroxy-2,6-dimethyloctan-3-one, and (2S,4R,7S)-2-iso­butoxy-7-isopropyl-4-methyloxepane. Possible ways of formation of each product have been proposed, and conditions for their selective formation have been found. The synthesis of oxepan-2-ol isobutyl acetals via low-temperature (–70°C) reduction of 7-membered lactones with diisobutylaluminum hydride in methylene chloride is considered. The synthesis of a number of low-molecular-weight bioregulators, including optically active pheromones of insect pests in agriculture and forestry, based on (–)-mentholactol, its aluminate, and (6R)-8-hydroxy-2,6-dimethyloctan-3-one is discussed.