Pyrazinyl- and pyrimidinylketenes, bisketenes, and ylides: direct observation and nucleophilic reactivity
Bibliographic record
Abstract
Pyrazinylketene (9) and 4-pyrimidinylketene (11), identified by their IR absorption at 2128 and 2130 cm−1, respectively, are formed in CH3CN as transient intermediates by photolysis of the corresponding diazoketones. The corresponding ylides 10 and 12 are formed concurrently as longer-lived intermediates identified by their distinctive IR and UV absorption. Reactions of 2-pyridylketene and of 9 and 11 with diethylamine form initial amide enol intermediates leading to dihydroheteroarene intermediates and then to amides, whereas amide enols are not observed in reactions with n-butylamine. Reactions with water give observable dihydroheteroarenes. 2,5-Bis(ketenyl)pyrazine (33) is formed by photolysis of 2,5-bis(diazoacetyl)pyrazine (32) together with the corresponding bis(ylide) 35. The latter is calculated to have two geometrically isomeric structures (bond-stretch isomers) with similar energies, one with a central six-membered aromatic ring and another with a 10-pi electron aromatic system.
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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) | 0.000 | 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) | 0.002 | 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 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".