Mechanistic Imperatives for Catalysis of Aldol Addition Reactions: Partitioning of the Enolate Intermediate between Reaction with Brønsted Acids and the Carbonyl Group
作者:John P. Richard、R. W. Nagorski
DOI:10.1021/ja9900297
日期:1999.5.1
catalyzed intramolecular aldol addition reaction of 2-(2-oxopropyl)benzaldehyde (1) to give the aldol adduct 3 proceeds via essentially irreversible formation of the acetone-like enolate intermediate 2, because reprotonation of 2 by a solvent of H2O or D2O (kHOH or kDOD) is much slower than intramolecular addition of the enolate to the carbonyl group (kc). The aldol addition reaction of 1 catalyzed by high
溶氧根离子催化 2-(2-氧代丙基)苯甲醛 (1) 的分子内醛醇加成反应得到醛醇加合物 3,通过基本不可逆的丙酮样烯醇化物中间体 2 的形成进行,因为 2 被 H2O 或D2O(kHOH 或 kDOD)比烯醇化物到羰基 (kc) 的分子内加成慢得多。由高浓度 3-取代奎宁环缓冲液催化的 1 的羟醛加成反应通过 1 的可逆去质子化得到烯醇化物 2,以及烯醇化物与羰基的限速加成。确定了 kc/kHOH = 35 的速率常数比,用于在分子内加成到羰基和通过溶剂水质子化之间分配烯醇化物 2。随着缓冲酸的酸度从 pKBH = 11.5 增加到 7.5,Bronsted 缓冲酸和分子内醛醇加成使 2 质子化的相应比率 kBH/kc (M-1) 从 7 增加到 450。数据显示,...