C-arylglycosides

C-Arylglycoside 137 is synthesized by the RhCl(Ph3P)3-catalysed intermolecular reaction of 135 with 136 [57],... 

Table 24 Synthesis of C-arylglycosides with triarylindium. Reproduced with permission from Elsevier...

L-enantiomer [137]). The final reduction step with cyanoboro hydride concluded the sequence to yield the C-arylglycoside 178. The corresponding C-aryl-glycals can also be prepared by water elimination of the hemiacetal using the Martin sulfurane (Ph2S[OC(CF3)2Ph])2) [138]. 

Kometani, T, Kondo, H, Fujimori, Y, Boron trifluoride-catalyzed rearrangement of 2-aryloxyte-trahydropyrans a new entry to C-arylglycosidation, Synthesis, 1005-1007, 1988. 

FIGURE 7.10 C-Arylglycoside chemical shifts and coupling constants. 

Before exploring the various preparations of C-arylglycosides, it should be noted that an added feature of these compounds is the ease with which stereochemistry can be assigned. Specihcally, a report by Bellosta et al. [100] showed that C-arylglucosides and C-arylmannosides exhibited characteristic differences in their chemical shifts and C-H coupling constants. As shown in Figure 7.10, the Ci carbon of the a anomers consistently appeared downheld from the (3 anomers. Additionally, the Vc-i,h-i coupling constants of the a anomers were approximately 10 Hz smaller than those for the (3 anomers. 

Because electrophilic aromatic substimtions have provided access to C-arylglycosides via intermolecular reactions, similar technology is available for effecting the intramolecular delivery of the aromatic species. For example, utilizing the furanosyl fluoride shown in Scheme 7.27, Araki et al. [115] achieved formation of an 83% yield of the bicyclic product on treatment with borontrifluoride etherate. Similar chemistry is known for methyl glycosides [116,117] and glycosyl acetates [118]. 

Toshima, K, Matsuo, G, Ishizuka, T, Nakata, M, Kninoshita, M, C-Arylglycosidation of unprotected free sugar, J. Chem. Soc., Chem. Commun., 1641-1642, 1992. 

Schmidt, R R, Frick, W, Haag-Zeino, B, Apparao, S, De-novo synthesis of carbohydrates and related natural products. Part 28. C-arylglycosides and 3-deoxy-2-glyculosonates via inverse type hetero-Diels-Alder reaction, Tetrahedron Lett., 28, 4045 -4048, 1987. 

C-Arylglycosides possess a stable C-C glycosidic linkage and exhibit a broad range of useful antitumor, antifungal and antibiotic properties. S.R. Pulley et al. developed a novel method for the synthesis of this important class of compounds by using the Dotz benzannuiation reaction between alkynyl glycosides and alkoxy phenyl chromium... 

Although the use of aluminum and tin reagents have provided fruitful approaches to the preparation of C-arylglycosides, the majority of this chemistry centers around reactions utilizing Lewis acid catalysis. Of particular importance are reactions proceeding via electrophilic aromatic substitution. This type of chemistry has been widely applied to a sugars bearing a variety of... 

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