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New Synthesis of 28‐Homobrassinolide from Stigmasterol
Author(s) -
Hazra Braja G.,
Kumar Tirunahari Pavan,
Joshi Padmakar L.
Publication year - 1997
Publication title -
liebigs annalen
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.825
H-Index - 155
eISSN - 1099-0690
pISSN - 0947-3440
DOI - 10.1002/jlac.199719970536
Subject(s) - chemistry , stigmasterol , dihydroxylation , yield (engineering) , regioselectivity , epoxide , ring (chemistry) , olefin fiber , permanganate , ketone , organic chemistry , hydroxylation , stereochemistry , enantioselective synthesis , chromatography , catalysis , materials science , metallurgy , enzyme
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.