Furanoid C-glycosides

For the production of 2,3-unsaturated furanoid C-glycosides, palladium-promoted addition/elimination reactions can be used to good advantage (Scheme 8). 

Isopropylldene-D-mannose and 2,3,, 6-tetra-O-benzyl-D-glucose have been converted to the octonic acid derivatives ( 7) and ( 8), respectively. Under Wittig conditions the former cyclized partially to give a furanoid C-glycoside (see Chapter 3) and the latter, when made by the Knoevenagel-Doebner conditions, isomerlzed... 

Outten, R A, Daves, D G Jr, Benzo[d]naphtho[l,2-h]pyran-6-one C-glycosides. Aryltri-n-hutylstannanes in palladium-mediated coupling with 2,3-dihydropyran and furanoid glycols, J. Org. Chem., 54, 29-35, 1989. 

Using a C-glycosidic furanoid sugar amino acid, McDevitt and Lansbury [11] prepared a saccharide-peptide hybrid with a three-atom linker, the dimer 26. The homodimer of this C-glycosidic sugar amino acid gave rise to a five-atom spacer as in compound 27 (O Scheme 7) these derivatives have not been reported in deprotected form. 

Derivatives of C-glycosides with ketonic groups within pyranose rings lose carbon monoxide on photoirradiation, and lead to furanoid analogues. ... 

Ireland and his co-workers have amplified their studies on the synthesis of furanoid and pyranoid glycals (Scheme 1) and their use in the synthesis of 2,3-unsaturated C-glycosides (see Chapter 3). ... 

Furanoid Compounds.—An n.m.r. proton-proton coupling constant method has been applied to the anomeric configurational determination of C-glycosidic analogues of 2-deoxy-D-e/yr/iro-pentofuranosides." ... 

Two methods based on the use of aldonolactones, mentioned in the above section on pyranoid Q-glycosides, can be used to obtain furanoid aryl C-glycosides and difluoromethyl analogues. 

The D-ribose derivative (98) was converted into the C-glycosides (99) and (100) via the 2- and E-alkenes as indicated in Scheme 40, the former product being used to prepare the 2,7-anhydride (loi). In a related study the effects of different groups and electrophiles on the electrophilic ring closure of compound (102) and related substances to a- and -furanoid and pyranoid products were examined. ... 

Furanoid Compounds.- Reaction of substituted D-rlbofuranosyl fluorides with silyl enol ethers and allyl trimethylsllane gives mainly a-C -glycosides. Similar reaction of 2,3,5-trl-O-benzyl-... 

Ten years later, Lubineau et al. reported the direct reaction of unprotected carbohydrates with acetylacetone in aqueous alkali media [11]. By application of this method, an access to different mixtures of furanoid and pyranoid structures of a- and P-configured C-glycosides [12] was obtained. The ratio of the products depends on the conditions of execution for this reaction and the carbohydrates deployed (Eq. 2, Scheme 2.1). This Knoevenagel/Michael/retro-Claisen-aldol cascade is carried out at high temperature (60-90°C) and is associated with the loss of a C2 fragment of the starting 1,3-dicarbonyl component (when used with acetylacetone). 

Amino glycosides.1 Furanoid or pyranoid glycals (2) when irradiated with this azodicarboxylate undergo a [4 + 2]cycloaddition to form a dihydrooxadiazine (3) in 70-80% yield. The adducts on treatment with methanol (TsOH) open with inversion at C, to give hydrazines (4), which furnish 2-amino glycosides (5) on hydrogenolysis and deprotection. 

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