Base-free palladium-catalyzed borylation of enol carboxylates and further reactivity toward deboronation and cross-coupling
Bibliographic record
Abstract
A series of base-free Pd-catalyzed borylation procedures are reported for a number of alkenyl carboxylates, with pivalates generally outperforming their acetate counterparts. High-throughput experimentation was used to discover and optimize these reactions using in situ generated catalyst systems. Mechanistic studies identified C–O oxidative addition to Pd(0) as the turnover-limiting step, with a variety of rates observed depending on substrate structure. One exemplar oxidative addition complex was isolated and fully characterized, including by X-ray crystallography. This complex undergoes rapid and complete reaction with excess B 2 Pin 2 at room temperature, confirming that no exogeneous base is required for transmetallation with the Pd(II) pivalate intermediate. Notably, gamma-lactone and lactam substrates lead to unstable alkenyl pinacol boronates, which undergo protodeboronation under acidic and basic aqueous conditions. Optimization of this protodeboronation resulted in a mild, two-step reduction of the C–O bond, achieving net-deoxygenation while leaving the alkene intact. In contrast, use of an alternative tetraalkoxydiboron source – B 2 EPin 2 – was successful in catalysis, and offered improved stability of the resulting organoboron species. This enables further reactivity, such as cross-coupling, without competing protodeboronation. • C–O borylation of cyclic enol carboxylates can be achieved using specific Pd-based catalysts • Multivariate screening experiments revealed suitable systems as a function of substrate structure • Gamma-lactone and lactam products are prone to protodeborylation, offering a mild method for net reductive deoxygenation • Protodeborylation can be suppressed by employing a more sterically hindered boronate
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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 | 0.001 | 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 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.001 |
| Insufficient payload (model declined to judge) | 0.002 | 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".