Cyclovitamins D3: the preparation of C6-ketocyclovitamin and its conversion to a ring B/C spirosteroid

✍ Scribed by Mordechai Sheves; Yehuda Mazur

• Book ID: 104237227
• Publisher: Elsevier Science
• Year: 1976
• Tongue: French
• Weight: 227 KB
• Volume: 17
• Category: Article
• ISSN: 0040-4039
• DOI: 10.1016/s0040-4039(01)85508-8

✦ Synopsis

we ham recently deecrib& the conversion of tit~in DJ (la) into the 6Emethylethcr of 3,5-cyclovitamin O3 and its reconversion to the starting vitamin. Although the labile conjugated triene system of vitamin O3 is protected in this methylether its use as an intermediate for vitamin functionalizations proved limited due to its instability. Looking for a compound better suited for this purpose we have found the C6-keto-derivative (4) which is both comparatively stable and easily reconvertible to the vitamin. We report here on the preparation of this ketone and its reactions leading to the formation of ring B/C spirosteroids. Vitamin O3 tosylate (lb) was solvolysed in aqueous acetone buffered with KWC03 to give the 6R-alcohol (6a in the s-trans conformation) (3a)* as the major product (60% yield). The structure of (3a) was inferred from its solvolysis with p.-toluenesulfonic acid in aqueous dioxane which restored the conjugated triene system, yielding a 2.5:1 ratio of vitamin and trans-vitamin O3 (2).

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