Novel Zinc (II)-Mediated Epimerization of 2‘-Carbonylalkyl-α-<i>C</i>-glycopyranosides to Their β-Anomers
Bibliographic record
Abstract
2'-Aldehydes and 2'-ketones of alpha-C-glycosides, including the gluco-, galacto-, and manno- series, were epimerized exclusively to their beta-anomers in good-to-excellent yields under basic conditions and in the presence of zinc acetate. The beta-stereoselectivity is independent of the neighboring group at 2-O-substitution of sugar substrates. Therefore, this provides a particularly useful method for the preparation of manno-beta-C-glycosides. The epimerization is likely initiated by the formation of Zn-enolate that is stabilized by intramolecular chelation to the pyranose ring-oxygen to form a syn chair-boat structure. Due to the activation generated by the Zn-O coordination, fission of the C1-O bond occurs, leading to opening of the pyranose ring, which is spontaneously followed by a change in conformation. The more stable anti chair-boat transition state is favored, and the subsequent hetero-intramolecular Michael addition results in the formation of beta-C-glycoside in a ring-closure step.
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How this classification was reachedexpand
Full frame distilled prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. Learned from the 10,348 direct Codex labels and 10,348 direct Gemma labels. Candidate is the union of thresholded teacher heads; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels or direct frontier model labels.
Codex and Gemma teacher scores by category
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.001 | 0.001 |
| Bibliometrics | 0.000 | 0.001 |
| Science and technology studies | 0.000 | 0.001 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.001 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.000 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one teacher head, not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".