Amination of Pyridylketenes: Experimental and Computational Studies of Strong Amide Enol Stabilization by the 2-Pyridyl Group
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Bibliographic record
Abstract
Laser flash photolyses of 2-, 3-, and 4-diazoacetylpyridines 8 give the corresponding pyridylketenes 7 formed by Wolff rearrangements, as observed by time-resolved infrared spectroscopy, with ketenyl absorptions at 2127, 2125, and 2128 cm(-1), respectively. Photolysis of 2-, 3-, and 4-8 in CH(3)CN containing n-BuNH(2) results in the formation of two transients in each case, as observed by time-resolved IR and UV spectroscopy. The initial transients are assigned as the ketenes 7, and this is confirmed by IR measurements of the decay of the ketenyl absorbance. The ketenes then form the amide enols 12, whose growth and decay are monitored by UV. Similar photolysis of diazoacetophenone leads to phenylketene (5), which forms the amide enol 17. For 3- and 4-pyridylketenes and for phenylketene, the ratios of rate constants for amination of the ketene and for conversion of the amide enol to the amide are 3.1, 7.7, and 22, respectively, while for the 2-isomer the same ratio is 1.8 x 10(7). The stability of the amide enol from 2-7 is attributed to a strong intramolecular hydrogen bond to the pyridyl nitrogen, and this is supported by the DFT calculated structures of the intermediates, which indicate this enol amide is stabilized by 12.8 kcal/mol relative to the corresponding amide enol from phenylketene. Calculations of the transition states indicate a 10.9 kcal/mol higher barrier for conversion of the 2-pyridyl amide enol to the amide as compared to that from phenylketene.
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Full frame distilled prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. Learned from the 10,348 direct Codex labels and 10,348 direct Gemma labels. Candidate is the union of thresholded teacher heads; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels or direct frontier model labels.
Codex and Gemma teacher scores by category
| 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 | 0.001 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.000 | 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 it