Synthesis and Reactions of 1,4‐Anhydrogalactopyranose and 1,4‐Anhydroarabinose – Steric and Electronic Limitations

Abstract

Scope and limitations of 1,4-anhydro sugars as precursors of glycofuranosyl building blocks are described. The experiments revealed that the choice of the substituents is very important for an efficient preparation as well as a successful ring-opening reaction of 1,4-anhydro sugars. DFT Calculations suggest that selective protonation of 1,4-anhydro sugars is the key to the selective ring opening in order to afford only furanosides.

Chemical Synthesis of Furanose Glycosides

“…Dehydration of galactopyranose and arabinopyranose glycosides having a free hydroxyl group at C4 (e.g., 24 and 25, Fig. 8) produce 1,4-anhydrosugar derivatives (26 and 27, respectively) (55,56). When treated with an acid and an alcohol, furanose glycosides are produced in preference to pyranosides (55,57,58).…”

“…8) produce 1,4-anhydrosugar derivatives (26 and 27, respectively) (55,56). When treated with an acid and an alcohol, furanose glycosides are produced in preference to pyranosides (55,57,58). This is an intriguing method for the formation of furanosides, which has also been used for the generation of furanose polymers (59,60).…”

The UDP-Galp mutase catalyzed isomerization: synthesis and evaluation of 1,4-anhydro-β-d-galactopyranose and its [2.2.2] methylene homologue

“…Additionally, Bz and TBS protecting groups were recently described as being unsuitable for the cyclization step. 52 To generate compound 9 with a free 4-hydroxyl group, regioselective ring opening of 4,6benzylidene was required, and this has been well documented. Although 4,6-benzylidene (1,3-dioxane) formation occurs cleanly from D-glucose via Evans' procedure, 65,66 in our hands with Dgalactose we always obtained low to moderate yield (30-50%) of 5 together with unreacted starting materials from the reaction mixture.…”

A Cascade “Prins‐Pinacol‐Type Rearrangement and C4‐OBn Participation” on Carbohydrate Substrates: Synthesis of Bridged Tricyclic Ketals, Annulated Sugars and C2‐Branched Heptoses

“…The structure as well as the absolutes tereochemistry of 5i was thus unambiguously confirmed by X-ray analysis [13] of 6 and supported by the spectraldata. [13] Although participation of a6 -OBn group leading to 1,6-anhydro sugars is well established, [14] to the best of our knowledge, direct participation of 4-OBn group appears to be unknown, thoughp articipation of af ree 4-OH leadingt o1 ,4-anhydro sugars is reported [15] in af ew cases. To rationalize the formation of this interesting product we propose that initially, BF 3 ·OEt 2 activates the aldehyde to form an oxocarbenium ion 8 (Scheme 3), via 7,w hich may follow one (or both) of the fol- [b] 1TMSOTf0 .1 CH 2 Cl 2 20 145 2BF 3 ·OEt 2 1C H 2 Cl 2 00.5 mixture 3BF 3 ·OEt 2 2C H 2 Cl 2 00.5 74 4BF 3 ·OEt 2 2C H 3 CN 00.5 62…”