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Total Synthesis of Woodrosin I—Part 2: Final Stages Involving RCM and an Orthoester Rearrangement
Author(s) -
Fürstner Alois,
Jeanjean Fabien,
Razon Patrick,
Wirtz Conny,
Mynott Richard
Publication year - 2003
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.200390026
Subject(s) - orthoester , chemistry , total synthesis , stereochemistry , carbene , ruthenium , glycoside , salt metathesis reaction , metathesis , glycosylation , enantioselective synthesis , butenolide , catalysis , combinatorial chemistry , organic chemistry , biochemistry , polymer , polymerization
The completion of the first total synthesis of the complex resin glycoside woodrosin I ( 1 ) is outlined using the building blocks described in the preceding paper. Key steps involve the TMSOTf‐catalyzed coupling of diol 2 with trichloroacetimidate 3 which leads to the selective formation of orthoester 5 rather than to the expected tetrasaccharide. Diene 5 , on treatment with catalytic amounts of the Grubbs carbene complex 6 or the phenylindenylidene ruthenium complex 7 , undergoes a high yielding ring closing olefin metathesis reaction (RCM) to afford macrolide 8 . Exposure of the latter to the rhamnosyl donor 4 in the presence of TMSOTf under “inverse glycosylation” conditions delivers compound 9 by a process involving glycosylation of the sterically hindered 2′‐OH group and concomitant rearrangement of the adjacent orthoester into the desired β ‐glycoside. This transformation constitutes one of the most advanced applications of the Kochetkov glycosidation method reported to date. Cleavage of the chloroacetate followed by exhaustive hydrogenation completes the total synthesis of the targeted glycolipid 1 .