2-Hydroxy-4,6-dimethoxyacetophenone (4) was glycosylated with 0-(2,3,4,6-tetra-O-benzy~-a-~-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)-~-hydroxyacetophenone (17) with the trichloroacetimidate 5 afforded the 0-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 (lb) and vitexin (la), respectively.
~~ ~~3,5-Dimethoxyphenol (2) was glycosylated with 0-(2,3,4,6tetra-0-benzyl-a-D-glucopyranosyl) trichloroacetimidate (1) and trimethylsilyl triflate (TMSOTf) as the promoter to yield the aryl C-glycoside 3 via a n 0-glycoside intermediate and subsequent Fries rearrangement. After formylation, the cou-marin C-glycoside 7 was synthesized either by Perkin reaction with acetic anhydride or by Wittig reaction followed by cyclization at 150°C. Deprotonation yielded the coumarin 8-C-glycoside 8, a dimethyl ether of an isomer of naturally occurring coumarin 6-C-glycosides. F O R OMe 2 1 RaoR RO RaoR RO of the aldehyde 4 with ethyl (triphenylphosphorany1idene)acetate gave in 63% yield the acrylate derivative 6 which
ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.
ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.