Hemiacetals, cyclic s. Lactols

A stable tetrahedral intermediate is more likely in the reduction of lactones, and DIBAL is most reliable in the reduction of lactones to lactols (cyclic hemiacetals), as in E.J. Corey s synthesis of the prostaglandins. The key step, the hydride transfer from Al, is shown in the green frame. 

A stable tetrahedral Intermediate Is more likely In the reduction of lactones, for the same reasons that cyclic hemiacetals are more stable than acyclic ones. DIBAL Is most reliable In the reduction of lactones to cyclic hemiacetals (also known as lactols), as In this reaction from E. J. Corey s synthesis of the prostaglandins. 

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