Studies on the Terpenoids and Related Alicyclic Compounds. XV. Reduction of α-Ketol Acetates of 5α-Santanolide and the Stereochemistry of O, O-Acyl Rearrangement of vic-Diol Monoacetates in the Cyclohexane Ring System

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Reduction of α-ketol acetates (5, 6, 7, and 8) of 5α-santanolide with NaBH₄ and LiAlH (OBu^t)₃ were investigated. The structure of diol monoacetates (9-16) was determined by means of spectroscopic methods and some chemical transformation reactions, oxidation and acetylation. Their conformations are discussed from their NMR data. O, O-Acyl rearrangement was observed in the NaBH₄ reduction of α-ketol acetates (5, 6, and 8). The acid-and base-catalyzed O, O-acyl rearrangements of diol monoacetates (9-16) were also investigated. The acyl migration mechanisms are proposed.