Free-Radical Epimerization of D- into L-C-(glycosyl)methanol Compounds Using 1,5-Hydrogen Atom Transfer Reaction
A simple epimerization of C-(α-D-Gly p )methanol into C-(β-L-Gly p )methanol compounds is described. The radical sequence involved homolytic cleavage of the C5–H bond by 1,5-hydrogen atom transfer promoted by the 1’-O-yl radical and subsequent hydride addition with inversion of configuration. This methodology allows the preparation of rare C-(β-L-Ido p )-, C-(β-L-Altp)-, C-(β-L-Gulp)-, C-(β-L-Allp)methanol glycosides starting from carbohydrates of the D-series. It can also be applied to transform L- into D-configured C-glycosyl compounds, as illustrated by the formation of C-(β-D-6dGulp)- and C-(β-D-6dAltp)methanol from readily accessible L-rhamno and L-fuco analogs, respectively. In further development of this procedure compounds with C-(β-L-Araf)- and C-(β-L-5dRibf)methanol structures have also been synthesized. The alkoxyl radicals were generated by reaction of the corresponding N-alkoxyphthalimides with nBu3SnH(D) and in comparative terms, by visible light-photocatalysis using the Hantzsch ester/fac-Ir(ppy)3 procedure. The influence of the sugar ring conformation and the electronegativity of the substituents on the stereochemical outcome will be addressed.
| Main Authors: | , , , , |
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| Other Authors: | |
| Format: | artículo biblioteca |
| Language: | English |
| Published: |
John Wiley & Sons
2022-01-18
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| Subjects: | C-Glycosides, C-H activation, Hydrogen transfer, Radical reactions, Regioselectivity, |
| Online Access: | http://hdl.handle.net/10261/258275 http://dx.doi.org/10.13039/100012000 http://dx.doi.org/10.13039/501100003329 |
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