Reversal of Stereoselectivity in Lithiation of Ferrocenyl‐imidazolones: Epimeric Substrates lead to Planar Chiral Enantiomers
Bibliographic record
Abstract
Abstract Diastereoselective induction of planar chirality in ferrocenes often employs chiral sulfur‐, carbon‐ or phosphorus‐based directing groups. The origin of stereoselectivity in these reactions may be classified as (a) cyclopentadiene (Cp) ring‐controlled or (b) base‐controlled. These two categories are represented by auxiliaries that typically have stereogenic centers α or γ to the ferrocene core, respectively. In this study, it is shown that (−)‐2‐ferrocenyl‐1 S ‐triethylsilyloxy‐7a S ‐hexahydropyrrolo[1,2‐ c ]imidazol‐3‐one, the anti ‐epimer of the previously reported syn ‐(1 R ,7a S ) substrate, induces lithiation of the pro‐ R p rather than the pro‐ S p Cp hydrogen in >95:5 dr , leading to enantiomers of the syn ‐derived planar chiral imidazolones upon electrophile quench and elimination. This outcome provides a practical way to prepare planar chiral enantiomers in this series without having to synthesize a more expensive D ‐proline‐derived starting material, since both the syn and anti starting materials are available from a common L ‐proline‐derived intermediate. The origin of stereoselectivity in lithiation of the syn and anti epimers, which have β,γ‐stereogenic centers, appears to be driven primarily by the conformational bias exerted by the β‐silyloxy moiety in each chiral auxiliary, which positions the urea carbonyl within the proximity of one of the two prochiral ortho Cp hydrogens. As such, stereoselectivity is likely Cp ring‐controlled for both compounds despite their lack of α‐ferrocenyl stereogenic centers. This conclusion is supported by the insensitivity of lithiation selectivity to the bulkiness of the base, comparisons of enantiomers, deuteration experiments, nOe difference studies, and computational modeling of the ground states and lithiation transition states for both substrates.
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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) | 0.001 | 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) | 0.002 | 0.001 |
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".