On the Mechanism of Gold(I)‐Catalyzed Ring Expansion of Cyclopropanols: Theoretical Calculations Uncover a Bottle‐Neck 1,4‐H Shift and Suggest Adequate Reaction Conditions
Bibliographic record
Abstract
Abstract The mechanism of the one‐carbon ring‐expansion reactions of 1‐(1‐propynyl)cyclopropanol ( 1 ; R = Me), (1 R *,2 R *)‐1‐ethynyl‐2‐isopropylcyclopropanol ( 3 ), and (1 R *,2 S *)‐1‐(phenylethynyl)‐2‐isopropylcyclopropanol ( 4 ) catalyzed by [AuP(Ph) 3 ] + to yield the corresponding 2‐alkylidenecyclobutanones was theoretically investigated by B3LYP‐PCM calculations by using the LANL2DZ relativistic effective core potential for Au and the 6‐31G(d) basis set for the remaining atoms. The most favorable route for these rearrangements in dichloromethane solution is a two‐step mechanism involving as the first step the coordination of the gold(I) complex to the alkyne moiety with subsequent evolution through a 1,2‐alkyl shift. Activation of the reactive C–C bonds takes place mainly through hyperconjugative interactions of these bonds with the oxygen atom and the alkyne moiety; this latter interaction is reinforced by the presence of the cationic gold(I) complex. The second step is the rate‐determining one and consists of a 1,4‐H shift, which requires the assistance by a second molecule of cyclopropanol to become readily accessible. This second molecule plays a very efficient bifunctional catalytic role, which cannot be played by a dichloromethane molecule. The use of methanol, water, and HFIP as assisting molecules was also investigated. Calculations suggest that the process would run most favorably in water. In agreement with experimental data, we found that the most favorable ring expansion of 3 takes place through migration of the substituted carbon atom. The only product to be expected from the rearrangement of 4 , however, is that corresponding to the migration of the nonsubstituted carbon atom.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)
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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) | 0.001 | 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 | 0.001 |
| Open science | 0.001 | 0.000 |
| Research integrity | 0.001 | 0.000 |
| Insufficient payload (model declined to judge) | 0.004 | 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".