Glycals 2-deoxy-2- glycoside

Scheme 5.56 Routes to 2-amino-2-deoxy-glycosides from glycals.

In recent studies, acceptable yields of (3-configurated 2-deoxy glycosides by application of the NIS reaction to uronic ester glycals like 38 have been reported [19]. By NMR studies the equilibrium conformation of the glycal 38 is shown to be shifted towards the inverted half-chair or half-boat conformation [5H4(D)]. 

Scheme 34. Routes to 2-deoxy- -glycosides from glycals...

Seeberger et al., 1997 Lehmann, 1976, 1996). Glycals are versatile synthetic intermediates in the synthesis of 2-deoxy- and 2-amino-glycosides (see Scheme 4.4.5) (Fraser-Reid, 1975 Fraser-Reid and Anderson, 1980). Reaction of glycal and alcohol in the presence of promoters (Ag+/1, NBS) and subsequent reductive dehalogenation (Hj-Pd, Bu SnH-AiBN) produces preferentially the 2-deoxy-(-glycoside. 

Addition to various glycals of pentane-2,4-dione-3-thione in pyridine gave hetero Diels-Alder adducts of the type 11. On methylenation these compounds gave the dienes, e.g. 12, which ring-opened on treatment with alcohols in the presence of triflic acid to give 2-thio-compounds which, on reductive desulfurization, afforded 55-95% yield of P-2-deoxy-glycosides including disaccharides (Scheme 1). ... 

Compound 13, the product of cycloaddition between a,oc-dioxothiones and tri-6>-benzyl-D-glucal (see Vol. 29, Chapter 11, Ref. 11) has been used to prepare 2-deoxy-glycosides, as shown in Scheme 1. The cycloaddition reaction has now been applied to several other glycal- and a,a-dioxothione-derivatives. ... 

The enantiomer of (17) was synthesised from L-rhamnal by an analogous procedure. Hethylation at 0-4 of the monosilyl ether (46) with butyl lithium - methyl iodide was unsatisfactory due to desilylation, but a good yield (60-70%) of the desired product was obtained with one equivalent of methyl triflate and base (either BuLi or 2,6-di-tert-butylpyridine)Further details have been published on the cis-addition of Q,Q-dialkylphosphorodithioic acids to peracetylated glycals, and the conversion of the products into 2-deoxy-glycosides fc.f.. Vol.20, p.2l). By using the... 

The cycloaddition of trichloroacetyl isocyanate to some protected glycals, followed by methanolysis of the products, has afforded predominantly 2-aminocarbonyl-2-deoxy-glycosides, e.g.. 

Full details have been published on the [4+2]cyclo-addition of dibenzyl azodicarboxylate to O-silylated glycals, and the conversion of the adducts to 1,2-trans-related 2-amino-2-deoxy-glycosides by reaction with alcohol in the presence of an acid catalyst (c Vol.22, p.97). By using bis(trichloroethyl) azodicarboi late, this route has now been extended for use with acetylated... 

The 5-deoxy-fluoro-sugar derivatives (15) and (16) have been synthesised from D-glucose for incorporation into potential chemotherapeutic nucleosides. Improvements to Ogawa s method for the synthesis of 2-deoxy- -glycosides, involving addition of arylsulphenyl esters of the desired aglycon to glycals, with... 

A new method for the preparation of 2-amino-2-deoxy-glycosides involved the cycloaddition of dibenzyl azodicarboxylate to glycals. Puranoid and pyranoid glycals, (23) and (2M), gave single cycloadducts (25) and (26) which methanolysed with inversion at C-1 to provide glycosides (27) and (28), respectively (Schemes 5 and 6). 

Michalska [95, 96] introduced 5 -(2-deoxyglycosyl)phosphorodithioates for the synthesis of 2-deoxy-glycosides. 0,0-DialkyIphosphorodithioic acids add to acylated (144) or benzylated glycals in benzene (Scheme 33) to give predominantly crystalline a-adducts (145). 

Methyl glycosides of 2 deoxy sugars have been prepared by the acid catalyzed addition of methanol to unsaturated sugars known as glycals... 

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