Glycosyl imidates, 70. Synthesis of a coumarin C‐glucoside

Abstract

~~ ~~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

Biocatalytic C-Glucosylation of Coumarins Using an Engineered C-Glycosyltransferase

“…Given the various biological activities of coumarin derivatives, especially the effects of the C-glycosyl moiety on the activity, several examples of chemically synthesizing coumarin C-glycosides in which the C-3 or C-4 position contains a glycosyl residue have been described . The chemical synthesis of coumarin 8-C-glucosides has also been reported by Mahling and Schmidt . However, chemical C-glycosylation remains restricted by such disadvantages as poor regio- and stereoselectivities and the tedious protection and deprotection of functional groups .…”

An Efficient Copper-Catalyzed Three-Component Synthesis of 3-C-Linked Glycosyl Iminocoumarins

“…Consequently, the development of new and mild methods for constructing coumarin and iminocoumarin frameworks is an attractive goal. Since the first syntheses of coumarin C-glycosides by Mahling and Schmidt,16 many reports have appeared on the synthesis of C-glycosyl coumarin derivatives in which the aromatic ring of the coumarin unit is attached to the anomeric carbon of the sugar. 4j,17 However, there are few reports on the synthesis of coumarin 3-or 4-C-glycosides.…”

Synthesis of 1,1′-Diarylethanes and Related Systems by Displacement of Trichloroacetimidates with Trimethylaluminum

“…As trichloroacetimidates are typically activated with Lewis acids, a carbon nucleophile must be compatible with these conditions. Typically, these substitutions are limited to Friedel-Crafts type processes with electron rich aromatic rings acting as nucleophiles, 3h,7 although there have been reports of silyl enol ethers, allylsilanes and allylstannanes being effective nucleophiles under Lewis acid catalysis. 6b,8 Currently there are no reports on the displacement of trichloroacetimidates with stoichiometric amounts of alkylmetal reagents.…”