1,3‐Diethynylallenes: Stable Monomers, Length‐Defined Oligomers, Asymmetric Synthesis, and Optical Resolution
Bibliographic record
Abstract
Abstract A series of differently substituted 1,3‐diethynylallenes (DEAs) have been synthesized, confirming that the previously introduced construction protocols tolerate a variety of functional groups. The new DEAs bear at least one polar group to facilitate enantiomer separations on chiral stationary phases and to allow further functionalization. They are thermally and environmentally stable compounds since bulky substituents next to the cumulene moiety suppress the tendency to undergo [2+2] cyclodimerization. A series of length‐defined oligomers were obtained as mixtures of stereoisomers by oxidative coupling of a monomeric DEA under Glaser–Hay conditions. The electronic absorption data indicate a lack of extended π‐electron conjugation across the oligomeric backbone due to the orthogonality of the allenic π‐systems. Remarkably, even complex mixtures of stereoisomers only yield one single set of NMR signals, which underlines the low stereodifferentiation in acyclic allenoacetylenic structures. Optical resolution of DEAs represents an amazing challenge, and preliminary results on the analytical level are reported. Asymmetric synthesis by Pd‐mediated SN2′‐type cross‐coupling of an alkyne to an optically pure bispropargylic precursor opens another promising route to optically active allenes with stereoselectivities currently reaching up to 78 % ee. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)
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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 | 0.001 |
| 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".