New Synthesis of 28-Homobrassinolide from Stigmasterol

✍ Scribed by Hazra, Braja G. ;Kumar, Tirunahari Pavan ;Joshi, Padmakar L.

• Publisher: John Wiley and Sons
• Year: 1997
• Tongue: English
• Weight: 632 KB
• Volume: 1997
• Category: Article
• ISSN: 0947-3440
• DOI: 10.1002/jlac.199719970536

✦ Synopsis

Abstract

An efficient and short synthesis of 28‐homobrassinolide (6) has been achieved in 12 steps with 15.6% overall yield from stigmasterol (8). Salient features of this synthesis are: (a) use of tetradecyltrimethylammonium permanganate for chemoselective cis‐dihydroxylation of the 2,22__E__‐dien‐6‐one 9, avoiding the use of OsO~4~; (b) one‐step epoxidation of the (22__E__)‐olefin and Baeyer‐Villiger oxidation of the B‐ring ketone 11 with trifluoroperoxyacetic acid; and (c) regioselective ring‐opening of the 22,23‐epoxide 12 to the bromohydrin 13 with LiBr and Amberlyst‐15 resin under mild conditions and in excellent yield.