Synthesis of substituted phenols by directed <i>ortho</i>-lithiation of in situ <i>N</i>-silyl-protected <i>O</i>-aryl <i>N</i>-monoalkylcarbamates
Bibliographic record
Abstract
A simple, high-yield procedure has been developed for the ortho-lithiation and subsequent ortho-substitution of phenols by a manifold of electrophiles. N,C-Dilithiation of O-aryl N-monoalkylcarbamates proved to be impossible due to a cleavage reaction of the monolithiated intermediates. However, in situ N-silylation of O-aryl N-isopropylcarbamates proceeds smoothly with trialkylsilyl triflates N,N,N',N'-tetramethylethylenediamine (TMEDA). Separation of the formed O-aryl N-isopropyl-N-trialkylsilylcarbamates from the byproduct TMEDA·HOTf, which is insoluble in diethyl ether or toluene, is not required. ortho-Lithiation with n-butyllithiumTMEDA at 78°C leads to the corresponding aryllithium, which does not undergo anionic ortho-Fries rearrangement under the reaction conditions, but is efficiently substituted by electrophilic reagents. During the aqueous work-up, the N-silyl group is removed and the corresponding ortho-substituted O-aryl N-isopropylcarbamate is isolated. Among the introduced electrophiles are: Me3Si, Bu3Sn, PhS, I, Br, Cl, alkyl, α-hydroxyalkyl. Liberation of the free phenols is performed under mild alkaline conditions.Key words: directed ortho-metalation, ortho-lithiated O-aryl carbamates, ortho-substituted phenols, in situ protection of N-monoalkylcarbamates.
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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) | 0.001 | 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".