Hydration of Pyridylketenes: Formation of Acid Enol and Dihydropyridine (Eneaminone) Transients
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Bibliographic record
Abstract
2-, 3-, and 4-Pyridylketenes 4 formed in water by photochemical Wolff rearrangements using flash photolysis undergo rapid hydration forming transient intermediates observed by UV spectroscopy. 3-Pyridylketene (3-4) formed the acid enol intermediate 3-10 which was converted to the acid 3-11, and phenylketene gave similar behavior. 4-Pyridylketene (4-4) reacted with a similar initial rate constant of 5.0 x 10(4) s(-1) for decay of an absorption at 275 nm, with concomitant formation of a strong absorption at 370 nm with the same rate constant. The intermediate absorbing at 370 nm decayed with a lifetime 2.4 x 10(3) fold longer than that of the ketene, and is identified as 4-(carboxymethylene)-1,4-dihydropyridine (4-13), resulting from conjugate 1,6-addition of H(2)O to 4-4. 2-Pyridylketene (2-4) underwent hydration with a similar rate constant of 1.1 x 10(4) s(-1) forming a transient with a UV absorption with maxima at 310 and 380 nm that decayed with biexponetial kinetics, with rate constants slower than the rate of formation by factors of 5.2 and 110, respectively. These results are interpreted as indicating the presence of two species, namely Z- and E-2-(carboxymethylene)-1,2-dihydropyridines (2-13), resulting from conjugate 1,4-addition of H(2)O to 2-4. The identifications of the 1,2- and 1,4-(carboxymethylene)dihydropyridines 2- and 4-13 were confirmed by comparison of their UV spectra with those of the corresponding N-methyl derivatives. The amination of 2-pyridylketene in CH(3)CN was reinvestigated, and spectroscopic evidence, computational studies, and preparation of the N-methyl analogue demonstrated formation of the 1,2-dihydropyridine Z-2-8f as the long-lived intermediate.
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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 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.000 | 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