Reductive cleavage of cyclic orthoesters

Tietze has synthesized ethyl P-D-mannopyranoside from non-carbohydrate precursors [190]. The procedure involves [4-1-2] hetero Diels-Alder cycloaddition of the enol ether 122 and the chiral oxazolidinone 123 under promotion by Me2AlCl to give the dihydropyran 124 in very high diastereoselectivity. Reductive cleavage of 

In the alternative route [159, 195, 196] a p-glucopyranoside is synthesized first, followed by azide-displacement at C-2 to provide the 2-azido-2-deoxy-P-mannopyranoside unit in a process as reviewed for the parent compound in Section 13.2.2. 

Round bottomed flasks (1 X 10 ml, 1 X 25 ml) with rubber septa and magnetic stirrer bars Magnetic stirrer 

Experimental procedure. Safety glasses should be worn during the experiment and all manipulations should be performed in a fume cupboard. 

This chapter has illustrated the importance of the P-mannosidic linkage within biological systems, and problems encountered with its synthesis. A number of chemical preparative methods have been compared, but it is obvious that there is no one, ideal method of universal utility. As with all carbohydrate chemistry, a careful assessment of the proposed preparative route must be performed before a specific technique for the incorporation of the p-mannosidic linkage is selected and pursued. 

B Ernst, GW Hart, P Sinay, in Carbohydrates in Chemistry and Biology, Vol. 1, Wiley-VCH, Weinheim, 2000. 

JF Kennedy, CA White, in Carbohydrate Chemistry, Clarendon Press, Oxford, 1988. 

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Ohtake H, limori T, Bcegami S (1997) A highly stereoselective p-(l —> 4)-glycosidic bond formation by reductive cleavage of cyclic orthoesters. Tetrahedron Lett 38 3413-3414... 

A related approach to the stereoselective synthesis of glycosidic linkages is based on the reductive cleavage of cyclic orthoesters generated by two sugar moieties. 

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