Galactopyranose method

The only recorded example using this method in the sugar series is the chlorination of l,2 3,4-di-0-isopropylidene-D-galactopyranose (73) which affords in addition to the expected 6-chloro-6-deoxy derivative 74a, a 5,6-unsaturated derivative 75 as well. These products were separated by silica gel column chromatography no yields were given. 

Die in der Zuckerchemie iibliche Methode der Substitution einer Mesyloxy-Gruppe unter Waldenscher Umkehr wurde zur Darstellung der 2-Amino-2-desoxy-l,6-anhydro-p-D-gulopyranose aus dem 3-mesylierten Derivat der 2-Acetamido-2-desoxy-l,6-anhydro-p-D-galactopyranose aus-gentitzt... 

D. J. Ward, W. A. Szarek, and J. K. N. Jones, An evaluation of methods for the preparation of l,2 3,4-di-0-isopropylidene-a-D-galacto-hexodialdo-l,5-pyranose. Oxidation of l,2 3,4-di-0-isopropylidene-a-D-galactopyranose with lead tetraacetate/ pyridine, Carbohydr. Res., 21 (1972) 305-308. 

One method to overcome selectivity issues during telomerization is to chemically protect all but one alcohol functionality. The first example of telomerization with a protected sugar was performed by Zakharkin et al., who successfully telo-merized 1,3-butadiene with the primary alcohol of 1,2,3,4-di-O-isopropylidene-ot-D-galactopyranose [93]. 

Li, Z., Xiao, G., Cai, M. Studies on carbohydrates. XII. An improved Koenigs-Knorr method for highly stereoselective synthesis of 1-O-acyl-P-D-galactopyranose tetraacetates. Chin. Chem. Lett. 1992, 3, 711-712. 

The method is illustrated for methyl a-D-glucopyranoside, its 6-anomer and for P-D-glucopyranosyl-(l- -6)-Q galactopyranose. 

This reaction was then successfully applied in different modifications (—10% aqueous potassium hydroxide is mostly used), especially on the phenyl glycosides of aldohexopyranoses28 43 and of the corresponding oligosaccharides (see Sect. X,l,a), and still remains one of the methods frequently used for the preparation of l,6-anhydro-/3-D-glucopyranose31 38,40 (6) (for example, specifically labelled with carbon-14 see Ref. 44) and of l,6-anhydro-)3-D-galactopyranose.30,37 41,45 45a... 

The selectivity of alkylation of 1,6-anhydrohexopyranoses is lower than drat of acylations. The relative rate-constants for the three hydroxyl groups in 1,6-anhydro-jS-D-glucopyranose (6) during methyla-tion with dimethyl sulfate in 19% sodium hydroxide solution689 are k2 ks k4 = 2.5 1 1.8, so that the formation of pure monomethyl or dimethyl ethers of 6 by this method is of little preparative value (compare Refs. 224 and 671). l,6-Anhydro-/3-D-galactopyranose (12) affords mostly the 2,4-di-O-methyl derivative,690 and 2-acetamido-l,6-anhy-dro-2-deoxy-/3-D-galactopyranose is mainly methylated at 0-4 by the... 

Isopropylidene-a-D-galactopyranose crystallized, on long standing, from a preparation of the diacetal. A more convenient method is described by Unrau, who used nitric acid (1%) in ethyl acetate to effect the partial hydrolysis. A 1,6-aiihydro-3,4-0-isopropylidene-D-galactose has been isolated by fractional distillation of the products from a preparation of the diacetal. ... 

Oscarson et al. [5] found that benzoylation of 1 is often very slow when conventional methods are used, but it is dramatically accelerated under micro-wave activation. Benzoylation of selected substrates, for example acetonated a-D-galactopyranose and benzylidene 4,6-protected a-D-glucopyranose, which are not stable in acidic conditions, was performed by Cleophax et al. [13] under the action of microwave irradiation in a monomode system with methyl benzoate for 4-15 min. 

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