Lewis Acid Catalyzed Three-Component Hetero-Diels−Alder (Povarov) Reaction of <i>N</i>-Arylimines with Strained Norbornene-Derived Dienophiles
Bibliographic record
Abstract
Generally, the hetero-Diels-Alder reaction (Povarov reaction) of N-arylimine dienes are limited to reaction with activated, electron-rich alkenes. However, introduction of ring strain in the dienophile, as with moderately strained bicyclo[2.2.1]heptenes (norbornene), enables three-component Povarov reaction with in situ formed N-arylimines under Lewis acid catalyzed conditions (BF(3).OEt(2)). The reactions proceed efficiently with a diverse set of commercially available anilines and benzaldehydes, as well as a variety of substituted norbornenes. The corresponding tetrahydroquinolines are formed with high complexity in a multicomponent fashion and are obtained in good yield and high diastereoselectivity. In addition, more reactive ethyl glyoxylate derived imines were utilized to achieve faster, room temperature reactions with norbornene. In all cases, attack of the N-arylimine dienes occurred exclusively from the exo-face of the norbornene ring, but the relative stereochemistry of the substituent alpha to the tetrahydroquinoline nitrogen, as well as the regioselectivity of reaction, was shown to depend upon subtle substituent effects on the aniline precursors. In most cases, a preference for the formation of exo-exo diastereomeric adducts was observed, but for reactions of ortho- or meta-substituted anilines, the formation of exo-endo adducts was also observed. These observations may be rationalized by two competing mechanistic models, involving either a concerted asynchronous [4 + 2]-like mechanism or a stepwise mechanism.
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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) | 0.001 | 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".