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Glycosyl imidates, 69. Synthesis of flavone C ‐glycosides vitexin, isovitexin, and isoembigenin
Author(s) -
Mahling JürgenAndreas,
Jung KarlHeinz,
Schmidt Richard R.
Publication year - 1995
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.199519950362
Subject(s) - vitexin , isovitexin , chemistry , glycosylation , glycoside , yield (engineering) , glycosyl , stereochemistry , trifluoromethanesulfonate , fries rearrangement , trimethylsilyl , organic chemistry , catalysis , flavonoid , biochemistry , materials science , metallurgy , antioxidant
2‐Hydroxy‐4,6‐dimethoxyacetophenone ( 4 ) was glycosylated with O ‐(2,3,4,6‐tetra‐ O ‐benzyl‐α‐ D ‐glucopyranosyl) trichloroacetimidate ( 5 ) and trimethylsilyl triflate as promoter to yield directly the C ‐glycoside 6 . Construction of the flavone system by application of a Baker‐Venkataraman‐type rearrangement followed by deprotection yielded isoembigenin ( 2 ). Glycosylation of 4,6‐bis( tert ‐butyldimethylsilyloxy)‐2‐hydroxyacetophenone ( 17 ) with the trichloroacetimidate 5 afforded the O ‐glycoside intermediate 18 which was converted via Fries rearrangement into the C ‐glycoside 21 . Applying again the Baker‐Venkataraman rearrangement and cyclization gave isovitexin and vitexin derivatives 25 and 26 , which were completely deprotected to yield isovitexin ( 1b ) and vitexin ( 1a ), respectively.