Deoxygenative [1,2]-Hydride Shift Rearrangements in Nucleoside and Sugar Chemistry: Analogy with the [1,2]-Electron Shift in the Deoxygenation of Ribonucleotides by Ribonucleotide Reductases<sup>1</sup>
Bibliographic record
Abstract
A variant of the semipinacol rearrangement that was observed in our laboratory has been applied to the synthesis of several furanose and pyranose derivatives. The process consists of an "orchestrated" [1,2]-hydride shift with departure of a leaving group from the opposite face. Transient formation of a C=O group is followed by rapid transfer of a hydride-equivalent from the same face from which the leaving group departed, which results in double inversion of stereochemistry at the two vicinal carbon atoms. Treatment of 2'-O- and 3'-O-tosyladenosine with lithium triethylborohydride in DMSO/THF gave the respective 2'- and 3'-deoxynucleoside analogues with beta-D-threo configurations. Identical treatment of 5'-O-TPS-2'-O-tosyladenosine gave 9-(5-O-TPS-2-deoxy-beta-D-threo-pentofuranosyl)adenine. The same [1,2]-hydride shift and stereochemistry with the 5'-OH and 5'-O-TPS compounds demonstrated the absence of remote hydroxyl-group participation. Application of this process to other nucleoside 2'-O-tosyl derivatives gave the 2'-deoxy-threo compounds in good yields. The reaction-rate order was OTs approximately Br >> Cl for 2'-O-tosyladenosine, 2'-bromo-2'-deoxyadenosine, and 2'-chloro-2'-deoxyadenosine (all with beta-d-ribo configurations). Analogous results were obtained with mannopyranoside derivatives with either 4,6-O-benzylidene protection or a free OH group at C4. Deuterium labeling clearly defined the stereochemical course as a cis-vicinal [1,2]-hydride shift on the face opposite to the original cis OH and OTs groups followed by hydride transfer from the face opposite to the [1,2]-hydride shift. Synthetic and mechanistic considerations are discussed.
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.001 | 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 source (direct Gemma or distilled Codex), 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".