Studies on Terpenoids and Related Alicyclic Compounds. II. Bromination-Dehydrobromination of 2-Oxo-5β-santanolide

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Mono-and di-bromination of 2-oxo-5β-santanolide (I), and dehydrobromination of the bromoketones were carried out. Monobromides (II, III, IV, and V) and dibromides (VII and VIII) were obtained. The stereoformulae of these bromides (II-V, and VII-VIII) were determined by infrared, ultraviolet, nuclear magnetic resonance, and circular dichroism spectroscopy. The C-4 axial epimer of I was obtained by hydrogenation of the enone (IX), which was prepared from II. Dehydrobromination of dibromoketones (VII and VIII) under several conditions gave a mixture of XII to XVIII. These structures were confirmed from spectroscopic data. A mechanism of dehydrobromination of VII and VIII is discussed.