292
2
General Synthetic Methods
⊡ Scheme 24
hydroxyl group is placed at the β- or γ -positions with respect to the oxirane ring, formation
of other anhydrosugars with a different size of heterocyclic ring might be observed [1,3]. The
classical examples of such transformations are shown in > Fig. 16.
⊡ Figure 16
Selected examples of the rearrangement of sugar epoxides
3.2 Sugar Oxetanes, Oxolanes (THF), and THP Derivatives
These compounds are rather rare. One of the first examples was presented by Helferich
who prepared 3,5-anhydro-1,2-O-isopropylidene-α-D-xylofuranose (82) from the appropriate 3,5-dimesyl derivative by treatment with ethanolic potassium hydroxide [1]. Another
convenient approach to such derivatives utilized the reaction of 1,2-O-isopropylidene-5-Otriflate-α-D-glucofuranos-3,6-lactone (79) with base (K 2 CO 3 ) in methanol, which produced
the corresponding L-ido-anhydrosugar 80. This was done by opening of the lactone ring
with formation of the alcoholate at 3-OH, which substituted the triflate with inversion of the
configuration at the C-5 atom ( > Fig. 17).
The general methodology for the preparation of anhydropyranoses containing tetrahydrofuran and tetrahydropyran anhydro rings is described in the leading book for preparative
carbohydrate chemistry: “Methods in Carbohydrate Chemistry” [53]. 3,6-Anhydrofuranoses
2
General Synthetic Methods
⊡ Scheme 24
hydroxyl group is placed at the β- or γ -positions with respect to the oxirane ring, formation
of other anhydrosugars with a different size of heterocyclic ring might be observed [1,3]. The
classical examples of such transformations are shown in > Fig. 16.
⊡ Figure 16
Selected examples of the rearrangement of sugar epoxides
3.2 Sugar Oxetanes, Oxolanes (THF), and THP Derivatives
These compounds are rather rare. One of the first examples was presented by Helferich
who prepared 3,5-anhydro-1,2-O-isopropylidene-α-D-xylofuranose (82) from the appropriate 3,5-dimesyl derivative by treatment with ethanolic potassium hydroxide [1]. Another
convenient approach to such derivatives utilized the reaction of 1,2-O-isopropylidene-5-Otriflate-α-D-glucofuranos-3,6-lactone (79) with base (K 2 CO 3 ) in methanol, which produced
the corresponding L-ido-anhydrosugar 80. This was done by opening of the lactone ring
with formation of the alcoholate at 3-OH, which substituted the triflate with inversion of the
configuration at the C-5 atom ( > Fig. 17).
The general methodology for the preparation of anhydropyranoses containing tetrahydrofuran and tetrahydropyran anhydro rings is described in the leading book for preparative
carbohydrate chemistry: “Methods in Carbohydrate Chemistry” [53]. 3,6-Anhydrofuranoses