Substitution substituted glucals

P-Substituted glucals 645 and 646, bearing a benzyloxy and a phenylsulfanyl group, have been deprotonated with the Lochmann-Schlosser base and LDA or f-BuLi, respectively. After reacting with electrophiles, these intermediates provide functionalized C-... 

Yadav et al. explored the reaction of substituted anilines with 3,4,6-tri- O-acetyl-D-glucal to offer the tetrahydroquinoline moieties.134 Most yields are around 80% with excellent distereoselectivity and the reaction was carried out in water (Eq. 12.61). The primary disadvantages are that both CeCb and Nal are required in stoichiometric amounts. 

Unusually-substituted deoxy sugars are found in a number of biologically important natural products, and an application of iodoglycosylation for the preparation of these compounds is shown in Scheme 5.51 [142]. Protected glucals 1 or 14 were selectively converted into 2-deoxy-2-iodo-a-mannopyranosyl glycosides 56 or 57. The... 

Apparently these names were chosen solely upon the assumption that the course of the reduction of the acetates of the two substituted 2-hydroxy-glucals had been similar to that of 2,3,4,6-tetraacetyl-2-hydroxy-D-glucal... 

A different approach to selective O-substitution involves preferential replacement of existing groups. When tris-0-(tert-butyldimethylsilyi)-D-glucal is treated with phosphorus oxychloride-dimethylformamide complex in pyridine, the 0-6 silyl ether is selectively and efficiently replaced by a formate ester (Vilsmeier-Haack reaction).85... 

Simple alkylation can be accomplished by use of trialkylaluminums which, with Lewis acids, afford 1-C-alkyl products such as 90, available in 72% yield by reaction between di-O-acetyl-6-deoxy-D-galactal and trimethylaluminum in the presence of titanium tetrachloride in dichloro-methane at —78 °C.109 Importantly, the reaction can also be applied to 1-alkylglycals, also with high stereoselectivity, so that the doubly substituted compound 91 can, for example, be made by allylation of tri-O-acetyl-l-C-methyl-D-glucal. Its C-l epimer is available by C-methylation of the 1-C-allylglucal.110... 

Some of the most useful 2,3-unsaturated C-glycosyl derivatives are the allyl compounds such as 92, made by use of allyltrimethylsilane, and a notable feature of this compound is that it can be produced directly from tri-O-acetyl-D-glucal with DDQ as promoter.111 A further surprising feature of this C-allylation procedure, however, is its applicability to glycals that are not O-substituted. Reactions are carried out in dichloromethane-acetonitrile at low temperatures with trimethylsilyl triflate as catalyst, and almost quantitative yields of 2,3-unsaturated C-allyl glycosyl compounds are recorded, with the a anomers being formed almost exclusively.112... 

From D-glucal and its O-substituted derivatives one can thus theoretically form a- and /3-D-glucose as well as a- and /3-D-mannose. The steric course of the reaction is dependent on the choice of starting material and on the experimental conditions it can therefore be controlled to a certain degree. 

The steric course of the reaction of derivatives of D-glucal that are substituted at the hydroxyl of carbon 3 proceeds in chloroform solution somewhat differently.4-18 For example, triacetyl-D-glucal yielded predominantly l-benzoyl-3,4,6-triacetyl-D-glucose (XXII), which has a... 

The properties of lactal correspond in large measure with those of D-glucal, but one important difference is to be noted. The green color with hydrochloric acid and a pine splinter does not appear, because of the substitution of the hydroxyl at carbon atom 4 by the galactose residue.18,47... 

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