Further Studies on the Synthesis of <i>meso</i>‐Tetraarylazuliporphyrins under Lindsey−Rothemund Reaction Conditions and Their Conversion into Benzocarbaporphyrins
Bibliographic record
Abstract
Abstract Azulene has been shown to react with pyrrole and a series of aromatic aldehydes in the presence of boron trifluoride etherate to give meso‐tetraarylazuliporphyrins 6. Good yields of azuliporphyrins were obtained for benzaldehyde, 4‐chlorobenzaldehyde, 4‐bromobenzaldehyde, and 4‐iodobenzaldehyde, and under dilute conditions p‐tolualdehyde gave respectable yields. In each case, substantial amounts of meso‐tetraarylporphyrins were also formed and a minor fraction of carbaporphyrin by‐products could be detected, but otherwise no other macrocyclic products could be identified. 4‐Nitrobenzaldehyde gave relatively poor yields of the corresponding azuliporphyrin, while p‐anisaldehyde only gave trace amounts of product. Pentafluorobenzaldehyde gave variable results, although in this case a large number of additional by‐products were identified including N‐fused pentaphyrin, hexaphyrin, and higher order porphyrinoids, but no expanded azulene‐containing macrocycles could be detected. Azuliporphyrins undergo reversible nucleophilic substitution on the seven‐membered ring with pyrrolidine, benzenethiol, hydrazine, or benzylamine to give carbaporphyrin adducts. This property appears to facilitate an oxidative ring contraction of azuliporphyrins 6 with tert‐butyl hydroperoxide in the presence of potassium hydroxide to produce mixtures of benzocarbaporphyrins 19 and 20. Tetraaryl‐benzocarbaporphyrins exhibit slightly reduced diatropic ring currents compared to their meso‐unsubstituted counterparts, although their UV/Vis spectra are very porphyrin‐like and exhibit strong Soret bands near 450 nm. The benzocarbaporphyrins undergo reversible protonation to give monocationic and dicationic species. The latter involves C‐protonation to generate an internal CH2 within the macrocyclic cavity. X‐ray crystallography of tetraphenylbenzocarbaporphyrin 19a confirms that the preferred tautomer has the two NHs on either side of the indene subunit, in agreement with previous theoretical and spectroscopic studies. In addition, the presence of phenyl substituents at the 5,20‐positions was found to tilt the indene moiety substantially by 27.4(1)° relative to the [18]annulene substructure. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)
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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 | 0.000 |
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".