6-Lithio-2,3-dihydro-4<i>H</i>-pyran
Bibliographic record
Abstract
[72081-15-3] C5H7LiO (MW 90.05) (acyl anion equivalent which reacts with a variety of carbon and other electrophiles via substitution and 1,2-addition;2-6 after conversion to other organometallics via conjugate addition7 and Pd0-catalyzed coupling,5 the resulting adducts are utilized for the preparation of substituted cyclopentenones and cyclohexenones and polycyclic spiro acetals2-9) Alternate Name: 6-lithio-3,4-dihydro-2H-pyran. Physical Data: white to off-white, highly moisture and air sensitive solid which may be pyrophoric.10 13C NMR (22.625 MHz in d8 THF): δ 201.2, 111.1 , 62.8, 24.71, 20.99.10 Solubility: sol anhydrous THF, anhydrous ether, and mixtures of saturated hydrocarbons and THF; insol pure hydrocarbons. At high concentrations (> ca. 1M), the reagent will sometimes precipitate from THF–pentanes at −78 °C. Form Supplied in: not commercially available. Analysis of Reagent Purity: the extent of metalation can be assessed by deuteration of an aliquot and 1H NMR analysis of the recovered 2,3-dihydropyran,10 or by direct observation using 1H NMR.2, 11 The concentration of solutions of the reagent can be determined by titration.12 Preparative Methods: three basic preparative methods have been described: metalation with the t-BuLi–2THF complex (lemon yellow) in pentane at about −10 °C;2 metalation with n-BuLi or t-BuLi in hexane or pentane containing a catalytic amount of TMEDA at 0 °C to room temperature or slightly above (the reagent precipitates from solution);10, 13 or metalation with n-BuLi in hexanes at 50–60 °C for several hours (also results in a precipate of the lithium reagent).14 For difficult cases, the Schlosser base (n-BuLi/KO-t-Bu) has been used, usually followed by trapping with chlorotrialkylstannanes and transmetalation of 6-trialkylstannyl-2,3-dihydro-4H-pyran and substituted derivatives thereof with n-BuLi in THF at −78 °C,8, 15-21 or by palladium-catalyzed coupling of chlorotrialkylstannanes with enol triflates derived from δ-lactones.22 Purification: none is normally required; the reagent is used as prepared. Handling, Storage, and Precautions: the reagent is customarily utilized shortly after preparation. Solvents and reagents should be anhydrous and free of oxygen. Commercial 2,3-dihydropyran is distilled before use. Solutions of the reagent must be protected from air and moisture utilizing standard inert atmosphere/syringe techniques.
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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 | 0.001 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.020 | 0.014 |
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".