Biologically active glycosides from asteroidea, XXVII. Stereochemistry of the C-17 side chain of 26-homothornasterol B: Novel triethylaluminum-promoted rearrangement and alkylation of epoxy alcohols

✍ Scribed by Honda, Masanori ;Igarashi, Takashi ;Marubayashi, Nobuhiro ;Komori, Tetsuya

• Publisher: John Wiley and Sons
• Year: 1991
• Tongue: English
• Weight: 332 KB
• Volume: 1991
• Category: Article
• ISSN: 0947-3440
• DOI: 10.1002/jlac.1991199101108

✦ Synopsis

Abstract

The absolute configuration of 3,6‐di‐O‐acetyl‐26‐homothornasterol B (3) obtained previously besides the 3,6‐di‐O‐acetyl derivative (2) of (20__S__,24__S__)‐24‐ethylthornasterol A by aldol reaction^2a)^ of the mixture of (3__S__)‐3‐ethyl‐4‐methyl‐2‐(trimethylsiloxy)‐1‐pentene (7) and 3,4‐dimethyl‐2‐(trimethylsiloxy)‐1‐hexene (8) with (+)‐diacetylasterone (1) has been determined by X‐ray structural analysis as (20__S__,24__S__,25__R__)‐3β,6α‐diacetoxy‐20‐hydroxy‐24‐methyl‐26‐homo‐5α‐cholest‐9(11)‐en‐23‐one. On the basis of these results a novel rearrangement and alkylation of the epoxy alcohols 6, 9, 13, and 15 with triethylaluminium have been discovered and investigated. The reaction occurs when the C‐4 position adjacent to the epoxide ring is congested.