Aryl C-glycal

Reductive aromatization of furanoglycal-substituted quinols give aryl C-glycals that are not stable. However, these compounds can be converted to aryl C-furanoglycosides by hydroboration (9). 

Scheme 6. Regiocontrol in the Preparation of the Aryl C-Glycal Relies on the Availability of a Regiochemically Clean Substrate...

This strategy has been extensively used by Parker s group in the synthesis of C-glycosyl aromatic antibiotics (Scheme 2a,c,d,e) by transformation of the easily accessible quinol C-l glycals into aryl C-l glycals, and thence to C-glycosyl compounds.19... 

The method was first applied to the preparation of a number of simple alkyl and aryl C-l glycals,71 but since then the scope of this approach have been extended with the preparation of a small library of significant C-l glycals including steroidal, and glycerolipidic residues endowed with potential biological activity.72... 

A. M. Gomez, M. Casillas, S. Valverde, and J. C. Lopez, Expeditious entry to C-alkyl and C-aryl pyranoid glycals, Chem. Commun. (Cambridge), (1996) 2357-2358. 

Glycal-substituted quinols and quinol ketals, derived from the 1,2-addition of lithiated glycals to quinones or quinone monoketals, are versatile intermediates for the synthesis of aryl C-glycosides, providing access to all four substitution patterns found in the natural products. For example, reduction of a quinol provides a p-hydroxyaryl glycal (8 9,11 -> 12). On... 

Investigations of the reverse polarity (umpolung) approach to the preparation of aryl C-glycosides have revealed the novel chemistry of glycal-... 

Czemecki, S, Gniy, E, New route to C-glycosides, Tetrahedron Lett., 22, 437-440, 1981. Czemecki, S, Dechavanne, V, Arylation of glycals catalyzed by palladium salts novel synthesis of C-glycosides, Caru J. Chem., 61, 533-540, 1983. 

Palladium(O) catalysed coupling of 1-tributyltin-substituted glycals with aryl bromides has afforded 1,2-unsaturated aryl C-glycosides. ... 

Several other research groups have also made use of 1-iodo glycals in their syntheses of C-l alkyl and aryl glycals (Scheme 8). Vogel and co-workers reported the use of 1-iodo glycals in carbonylative Stille couplings with... 

C-aryl glycals in 75-92% yields. It consisted in the addition of aryllithium reagents to variously protected 2-deoxy-aldono-l,5-lactones, followed by treatment with a mixture of pyridine (Py), 4-(Dimethylamino)pyridine (DMAP), and trifluoroacetic anhydride (TFAA). 

The added advantage of the C (1 )-stannylated glycals is their abUity to participate in palladium-catalyzed coupling reactions with organic halides, a process independently reported by Beau [75] and Friesen [81]. Vinyl stannane 237 can be benzylated, allylated or acylated provided that appropriate catalysts are used [75,77] and representative examples are given in Scheme 59. The C-arylation of... 

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