Anomeric Anhydro Sugars
3.7
741
⊡ Scheme 4
⊡ Scheme 5
⊡ Scheme 6
In a similar approach, treatment of methyl glycosides with camphorsulfonic acid (CSA) in
toluene under Dean–Stark conditions provides a good route to functionalized 1,6-anhydro sugars. Heathcock and co-workers showed that oxidation of the difficult-to-separate mixture of the
1,6-anhydro-β-D-glucopyranose (6) and 1,6-anhydro-β-D-glucofuranose (7) allowed for easy
isolation of the desired ketone (8), by either chromatography or direct crystallization, depending on the reaction scale ( > Scheme 4) [21].
In the final method, glycals are transformed into various 1,6-anhydro sugar derivatives. Glycals may be efficiently cyclized to yield 1,6-anhydro-2,3-dehydro sugars, such as (10), by
the action of Lewis or Brønsted acids; this reaction is an intramolecular Ferrier glycosylation
( > Scheme 5) [22,23]. 1,6-Anhydro-2-deoxy-2-halo sugars are accessed through ‘halocyclization’ reactions of O-stannylated glycals with a source of halogen such as iodine, bromine, or
NIS ( > Scheme 6) [22,24,25,26].
3.7
741
⊡ Scheme 4
⊡ Scheme 5
⊡ Scheme 6
In a similar approach, treatment of methyl glycosides with camphorsulfonic acid (CSA) in
toluene under Dean–Stark conditions provides a good route to functionalized 1,6-anhydro sugars. Heathcock and co-workers showed that oxidation of the difficult-to-separate mixture of the
1,6-anhydro-β-D-glucopyranose (6) and 1,6-anhydro-β-D-glucofuranose (7) allowed for easy
isolation of the desired ketone (8), by either chromatography or direct crystallization, depending on the reaction scale ( > Scheme 4) [21].
In the final method, glycals are transformed into various 1,6-anhydro sugar derivatives. Glycals may be efficiently cyclized to yield 1,6-anhydro-2,3-dehydro sugars, such as (10), by
the action of Lewis or Brønsted acids; this reaction is an intramolecular Ferrier glycosylation
( > Scheme 5) [22,23]. 1,6-Anhydro-2-deoxy-2-halo sugars are accessed through ‘halocyclization’ reactions of O-stannylated glycals with a source of halogen such as iodine, bromine, or
NIS ( > Scheme 6) [22,24,25,26].