Glycals derivatives

Perrier RJ (2001) Substitution-with-Allylic-Rearrangement Reactions of Glycal Derivatives. 215 153-175... 

Unlike the behavior of 81, treatment of 2,3,5-tri-O-benzyl-D-ribofuranosyl bromide91 (110) with mercuric cyanide gave an ano-meric mixture of cyanides (111), which was reduced to an epimeric mixture of amines.92 Separation of this mixture by column chromatography gave the D-alio isomer (112), the D-altro isomer (113), and the glycal derivative (114). Compound 112 was, however, formed in moderate yield (18%), presumably because of a preponderance of the a anomer in the mixture of anomeric cyanides (111). Compound 112 was converted92 into the 1-ureido derivative (92) by treatment... 

Figure 2.4 Synthesis of glycosyl fluorides from 1,2-anhydro sugars and glycal derivatives.

Glycals can be glycosylated not only directly via electrophilic addition, cyclo addition, nucleophilic addition and rearrangement reactions but also indirectly by conversion into a range of other glycosyl donors. One of the most important classes of these glycal-derived donors, the 1,2-anhydro sugars, is discussed in detail in Section 1.3. 

These variety of glycal derivatives is of considerable synthetic value, and have been exploited by several research groups. In a report by Quayle and... 

In related work, Rutjes and co-workers reported a four-step protocol from conveniently protected sugar derivatives to substituted C-l glycals (Scheme 16).77 The key step in their synthetic route included RCM of highly functionalized a-alkoxyacrylates. The potential of these glycal derivatives was illustrated by their conversion to natural products such as DAH (3-deoxy-D-arabino-2-heptulosonic acid) or KDO (3-deoxy-D-manno-2-ulosonic acid). 

Scheme 6.20 Glycoside synthesis using glycal-derived glycosyl dithiophosphates.

Scheme 41 Synthesis a furanose-fused butyrolactone from a glycal-derived cyclopropane...

More recently, another methodology for sugar-fused butyrolactones employing glycal-derived cyclopropane precursors has been described by Chandrasekaran and co-workers (Scheme 44) [215]. In this case, hexofuranose- or hexopyranose-1,2-fused were cyclopropanated into compounds of type 181. After saponification with... 

The addition of zinc organometallics to in situ generated oxenium ions by the reaction of mixed acetals with TMSOTf " allows a highly stereoselective preparation of protected a r/-l,3-diols of type 223 (Scheme 66). The addition of TMSOTf triggers also the allylic substitution of glycal derivatives, providing the substitution products of type 224 with excellent regio- and diastereoselectivity. 

C-Allylglycosides are also obtained by reaction of 1 with glycal derivatives in the presence of TiCl4 (1 equiv.). In all cases, the principal C,-glycoside is the one produced by apparant axial attack at C, (with concomitant shift of the double bond to C2 C,).4... 

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