Remote Substituent Effects in Ruthenium-Catalyzed [2+2] Cycloadditions: An Experimental and Theoretical Study
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Bibliographic record
Abstract
The effects of a remote substituent on the regioselectivity of ruthenium-catalyzed [2+2] cycloadditions of 2-substituted norbornenes with alkynes have been investigated experimentally and theoretically using density functional theory. Most of the cycloadditions occurred smoothly at room temperature, giving the exo cycloadducts in excellent yields. Regioselectivities of 1.2:1 to 15:1 were observed with various substituents on the C-2 position of the norbornenes. Exo-C-2-substituents usually showed greater remote substituent effects on the regioselectivities of the cycloadditions than the corresponding endo-C-2-substituents. The regioselectivity of the cycloadditions with C-2 substituents containing an exocyclic double bond (sp2 hybridized carbon at C-2) are much higher than the cycloadditions with the exo and endo 2-substituted norbornenes. Theoretical studies predicted the same trends as experiment and matched the experimental product ratios well. The nature of the regioselectivity in this reaction is discussed. Different strengths of the pi(C5-C6)-->pi(C2-Y) or pi(C5-C6)-->sigma(C2-Y) orbital interactions in 2-substituted norbornenes result in different degrees of C5-C6 double bond polarization. Stronger C5-C6 polarization will increase the difference in the activation energies between the major and minor pathways and thus lead to greater regioselectivities.
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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) | 0.001 | 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.
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