use of tartaric acid derivatives as chiral auxiliaries in the palladium-catalyzed cross-coupling of optically active cyclopropylboronic acids with electrophiles. The absolute configuration of the chiral carbon atom is retained, and the reaction proceeds with good yields and enantiomeric excesses. R=H, p-Ph, o-CO2 CH3 , p-CO2 CH3 , p-NO2 , o-OCH3 , m-OCH3 .
Palladium-Catalyzed Cross-Coupling Reaction of Cyclopropylboronic Acids with Aryl Triflates
作者:Min-Liang Yao、Min-Zhi Deng
DOI:10.1055/s-2000-6313
日期:——
In the presence of appropriate base and NaBr, the Suzuki-type reaction of aryl triflates and trans-cyclopropylboronic acids proceed readily to give pure trans-cyclopropylarenes in good to high yields. For the reaction of general aryl triflates, the base KF · 2 H2O is efficient, but in the case of aryl triflates bearing electron donating groups, KF · 2 H2O as a base makes the unexpected phenyl-aryl exchange between the phenyl of Pd(PPh3)4 and the aryl of triflate to occur. The use of K3PO4 · 3 H2O instead of KF · 2 H2O can inhibit the unexpected phenyl-aryl exchange, but the yield of the product is somewhat decreased. The coupling reaction of aryl triflates with the optically active cyclopropylboronic acids, which were easily obtained in good yield and with good to excellent ee (up to 94%) by the asymmetric cyclopropanation of alkenylboronates with optically pure TMTA auxiliary, was also investigated. During the coupling reaction, the absolute configuration of the cyclopropyl group was retained. Thus, a novel method to prepare aryl-substituted cyclopropanes, including highly optically active cyclopropanes, from phenols or arylamines was provided.
One-Bond-Nucleophilicity and -Electrophilicity Parameters: An Efficient Ordering System for 1,3-Dipolar Cycloadditions
作者:Le Li、Robert J. Mayer、Armin R. Ofial、Herbert Mayr
DOI:10.1021/jacs.2c13872
日期:——
place due to the existence of a previously overlooked lower-lying unoccupied molecular orbital. We now propose an alternative approach to analyze 1,3-dipolar cycloaddition reactions, which relies on the linearfreeenergyrelationship lg k2(20 °C) = sN(N + E) (eq 1) with two solvent-dependent parameters (N, sN) to characterize nucleophiles and one parameter (E) for electrophiles. Rate constants for the
重氮烷烃是双亲性 1,3-偶极子,与富电子和缺电子亲偶极分子发生快速 Huisgen 环加成反应,但与低极性烯烃反应缓慢。考虑到重氮烷炔丙基片段的 3 中心 4 电子 π 系统的前沿分子轨道 (FMO) 理论通常用于使这些反应趋势合理化。然而,我们最近发现,由于先前被忽视的低位未占分子轨道的存在,从环加成到偶氮偶联的机制发生了变化。我们现在提出了一种分析 1,3-偶极环加成反应的替代方法,该方法依赖于线性自由能关系 lg k 2 (20 °C) = s N ( N +E ) (eq 1) 具有两个溶剂相关参数 ( N , s N ) 来表征亲核试剂和一个参数 ( E ) 用于亲电试剂。测量了重氮烷烃与亲偶极体的环加成反应的速率常数,并与方程式 1 计算的两性离子形成速率常数进行了比较。实验吉布斯活化能与预测吉布斯活化能之间的差异被解释为协调能,即过渡的稳定性通过协调形成两个新债券的状态。通过将亲核偶极体的
Kinetic study of the homolytic brominolysis of 1,2-diarylcyclopropanes