Insight into the Mechanism and Stereochemistry of the Transformations of Alkyltitanium Ate‐Complexes. An Enhanced Enantioselectivity in the Cyclopropanation of the Carboxylic Esters with Titanacyclopropane Reagents
Bibliographic record
Abstract
Abstract The dependence of the stereoselectivity of the cyclopropanation reaction of γ,γ‐diphenyl‐γ‐butyrolactone and carboxylic esters with alkylmagnesium bromides in the presence of titanium(IV) TADDOLates on the structure of the reactants has been examined in detail. It has been found that the enantioselectivity in the formation of cis‐1,2‐disubstituted cyclopropanols is a function of the structure of the carboxylic ester alkoxy group and leads, in the case of cyclopropanation of hexafluoroisopropyl alkanoates, to 84% ee. To rationalize these observations, as well as the NMR data on the structures of the TADDOL‐derived alkyltitanium species, a new mechanistic model for the formation of the five‐coordinated chiral titanacyclopropane reactive intermediates and their subsequent reorganization in the reactions with esters is proposed. The essential features of this model consist in the generation of configurationally stable TADDOL derived titanacyclopropane species with an apical or equatorial position of the stereogenic carbanion center which is followed by retention or inversion of absolute configuration in course of the displacement of the carboxylic ester alkoxy group. magnified image
Fetched live from OpenAlex and de-inverted. Abstracts are not stored in this database: the inverted indexes are 8.6 GB of the frame’s 9.3 GB of text, and the host has 13 GB free.
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) | 0.003 | 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".