シアノ安定化グリニャード試薬の立体化学逆転:エステル溶剤の構造と濃度の顕著な効果
Ming Gao1, Neeraj N Patwardhan, Paul R Carlier
1Department of Chemistry, Virginia Tech , Blacksburg, Virginia 24061, United States.
Journal of the American Chemical Society
|August 28, 2013
まとめ
溶媒の同一性および濃度は,キラルグリナード反応剤の構成安定性に大きく影響する. THFや2-MeTHFのようなエーテル溶媒は,ダイエチルエーテルと比較してエピメリゼーションの速度を加速し,非対称な合成結果に影響します.
科学分野:
- 有機金属化学 有機金属化学
- アシンメトリック・シンセシス
- ステレオ化学 ステレオ化学
背景:
- チラルの有機金属反応剤は,非対称合成に不可欠です.
- これらの反応剤の構成安定性は,成功する反応に不可欠である.
- 溶媒効果など,安定性に影響する要因を理解することが重要です.
研究 の 目的:
- キラルグリナード反応剤のエピメリゼーションを調査するために.
- 構成の安定性に対するエステル溶剤の影響を決定する.
- エピメリゼーション率に対する溶媒同一性と濃度の影響を定量化するために.
主な方法:
- ブロモニトリルのMg/Br交換により,キラルグリナード反応剤が形成されます.
- 低温 (195 K) でエピメリゼーション速度定数 (k(tc)) の測定.
- デュテレーション産物のダイアステロエーマー比率を時間とともに分析する.
- ステキオメトリーと,様々なエーテル溶剤とトロウエンの濃度依存研究.
主要な成果:
- Mg/Br交換は,ダイエチルエーテル (Et2O) で高い保持率を示したが,2-MeTHFとTHFでは少ない.
- エピメリゼーションの速度は溶媒によって劇的に変化した:Et2Oでは26倍,2-MeTHFでは800倍,THFでは1300倍,トルーエンの0.12M Et2Oと比較して.
- グリニャール反応剤はEt2Oにヘテロジマーとして存在し,エピメリゼーションは脱集積を必要としない.
- 分析は,速度を制限するイオン対分離に先立つ急速なインクリメンタル溶解を示した.
結論:
- 溶媒の同一性および濃度は,キラルグリナード反応剤の構成安定性に大きく影響する.
- この研究では,溶媒リガンド捕獲の推定エントロピーコスト (-13 ± 3 eu) を示しています.
- 潜在的な"イオン誘導ツアー"のエピメリゼーション経路が提案され,計算的にサポートされました.
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